sensors
Review
Recent Advances of MEMS Resonators for Lorentz
Force Based Magnetic Field Sensors: Design,
Applications and Challenges
Agustín Leobardo Herrera-May 1, *, Juan Carlos Soler-Balcazar 2 , Héctor Vázquez-Leal 3 ,
Jaime Martínez-Castillo 1 , Marco Osvaldo Vigueras-Zuñiga 2 and Luz Antonio Aguilera-Cortés 4
1
2
3
4
*
Micro and Nanotechnology Research Center, Universidad Veracruzana, Calzada Ruiz Cortines 455,
Boca del Río, Veracruz 94294, Mexico; jaimartinez@uv.mx
Engineering Faculty, Universidad Veracruzana, Calzada Ruiz Cortines 455, Boca del Río, Veracruz 94294,
Mexico; jsoler@uv.mx (J.C.S.-B.); mvigueras@uv.mx (M.O.V.-Z.)
Electronic Instrumentation Faculty, Universidad Veracruzana, Cto. Gonzálo Aguirre Beltran S/N, Xalapa,
Veracruz 91000, Mexico; hvazquez@uv.mx
Departamento de Ingeniería Mecánica, DICIS, Universidad de Guanajuato,
Carr. Salamanca-Valle de Santiago km 3.5+1.8 km, Palo Blanco, Salamanca, Guanajuato 36885,
Mexico; aguilera@ugto.mx
Correspondence: leherrera@uv.mx; Tel.: +52-229-775-2000 (ext. 11956)
Academic Editor: Stephane Evoy
Received: 23 May 2016; Accepted: 12 August 2016; Published: 24 August 2016
Abstract: Microelectromechanical systems (MEMS) resonators have allowed the development
of magnetic field sensors with potential applications such as biomedicine, automotive industry,
navigation systems, space satellites, telecommunications and non-destructive testing. We present
a review of recent magnetic field sensors based on MEMS resonators, which operate with Lorentz force.
These sensors have a compact structure, wide measurement range, low energy consumption, high
sensitivity and suitable performance. The design methodology, simulation tools, damping sources,
sensing techniques and future applications of magnetic field sensors are discussed. The design
process is fundamental in achieving correct selection of the operation principle, sensing technique,
materials, fabrication process and readout systems of the sensors. In addition, the description of
the main sensing systems and challenges of the MEMS sensors are discussed. To develop the best
devices, researches of their mechanical reliability, vacuum packaging, design optimization and
temperature compensation circuits are needed. Future applications will require multifunctional
sensors for monitoring several physical parameters (e.g., magnetic field, acceleration, angular ratio,
humidity, temperature and gases).
Keywords: Lorentz force; magnetic field sensor; MEMS; resonators; sensing technique
1. Introduction
Microelectromechanical systems (MEMS) allow the development of devices that are composed
by mechanical and electrical components with a feature size in the micrometer-scale. MEMS devices
include signal acquisition and processing, actuators and control mechanisms [1]. These devices
provide the following advantages: small size, low power consumption, high sensitivity and reduced
fabrication cost [2]. Recently, several researchers [3–8] have designed MEMS magnetic field sensors for
potential applications such as biomedical, telecommunications, navigation and non-destructive testing.
Most of these sensors include resonators that operate with the Lorentz force, which is generated by the
interaction between an external magnetic field and an electrical current. It causes deformations of the
resonators, which are increased at resonance. These deformations can be measured using capacitive,
Sensors 2016, 16, 1359; doi:10.3390/s16091359
www.mdpi.com/journal/sensors
Sensors 2016, 16, 1359
2 of 25
piezoresistive and optical sensing techniques. Thus, MEMS sensors can have better resolution than Hall
effect and search coil sensors [9]. On the other hand, a superconducting quantum interference device
(SQUID) is expensive and requires a sophisticated infrastructure [10]. Other conventional devices
include the anisotropic magnetoresistive (AMR) and fluxgate sensors. Auto-calibration systems are
necessary for AMR sensors, which are saturated with small magnetic fields (close to few mT) [11,12].
Otherwise, fluxgate sensors need a complex fabrication of their magnetic core and coils [13].
MEMS magnetic field sensors use a bias source and a signal processing system. For instance,
Dominguez-Nicolás et al. [4] designed a signal conditioning system, implemented in a printed circuit
board (PCB), for a MEMS magnetic field sensor. It obtains the sensor response in voltage or current
mode for a magnetic field range from −150 µT to +150 µT. The sensor employs a virtual instrument
design through Labview software to visualize the 4–20 mA output signal. For industrial applications,
the sensor response is processed with a data acquisition card and a programmable logic controller
(PLC). Thus, MEMS sensors could commercially compete against conventional magnetic field sensors
in a wide variety of applications.
2. Design and Fabrication
Design stage is very important in determining the suitable structural configuration, materials,
operation principle and sensing technique of MEMS magnetic field sensors. In this stage, MEMS
designers can use analytical and numerical methods to predict the performance of MEMS sensors.
Designers must consider the rules of the fabrication process to avoid mistakes that affect the
performance of the sensors. To obtain reliable designs, designers must have a high level of fabrication
and packaging knowledge. In the design stage, simulation and modeling tools are necessary to predict
the behavior of MEMS sensors. These tools assist designers in selecting the best fabrication process
and materials for the sensors. To develop commercialized MEMS sensors, designers must satisfy
the following criteria: (1) optimal design; (2) packaging design; (3) reliable materials properties and
standard fabrication process; (4) suitable design and simulation tools; (5) reduction of electronic noise
and parasitic capacitances; (6) reliable signal processing systems and; (7) reliability testing.
The selection of the sensors fabrication process must consider several factors such as materials,
operation principle, dimensions, operating environmental conditions, signal conditioning processes
and sensing techniques [14]. The design rules of each fabrication process must be considered
during the sensors design stage. For this design, several MEMS design tools can be used including
MEMSCAP™ [15], coventorWare™ [16], IntelliSuite™ [17] and Sandia Ultra-planar Multi-level MEMS
Technology (SUMMiT V) [18]. These design tools have modules to create the sensor layout and check
the design rules, as well as simulating the steps of the micromachining process. These advantages
may reduce the work time related to the sensor’s design. In addition, the suitable design of a sensor
depends on the designer’s experience in using efficient methodology processes in the selection of
better materials and micromachining processes. Figure 1 depicts the layout of a magnetic field sensor
based on the SUMMiT V process [19].
Designers could employ the following methodology to design and fabricate MEMS magnetic
field sensors:
(1)
Application specification. In this stage, designers must know all the technical information of
the sensor application such as magnetic field range, environmental conditions, response time
and resolution.
(2) Conceptual design. This stage includes several conceptual designs of magnetic field sensors to
satisfy the requirements of the applications. Next, these designs are evaluated to select the best
conceptual design.
(3) Detailed design. Analytical and numerical methods are used to predict the sensor’s performance.
These designs must incorporate the sensor packaging, which depends of different factors
such as materials, operation pressure, cost, sensing technique and environmental conditions.
High temperatures can be generated during the sensor packaging, affecting its behavior. For this,
Sensors 2016, 16, 1359
3 of 25
Sensors 2016, 16, 1359
3 of 25
element finite method (FEM) models can be used to estimate the packaging temperature effect on
For this, element finite method (FEM) models can be used to estimate the packaging
thebehavior.
sensor behavior.
temperature
effect Designers
on the sensor
behavior.
(4) Fabrication process.
identify
the sensor requirements and characteristics of potential
(4)
Fabrication
process.
Designers
identify
sensorthe
requirements
and characteristics
of potential
fabrication processes. Next, the designerthe
selects
best fabrication
process or develops
a new
fabrication processes. Next, the designer selects the best fabrication process or develops a new
process, in which must consider the materials, etching steps, design rules, technical limitations
process, in which must consider the materials, etching steps, design rules, technical limitations
and cost.
and cost.
(5) (5)Material
properties verification. Test structures can be fabricated on the same sensor wafer to
Material properties verification. Test structures can be fabricated on the same sensor wafer to
measure
several
materials
sensorssuch
suchasasYoung’s
Young’s
modulus,
facture
strength,
measure several
materialsproperties
properties of
of the
the sensors
modulus,
facture
strength,
thermal
conductivity,
electrical
resistivity
and
dielectric
constant.
thermal conductivity, electrical resistivity and dielectric constant.
(a)
(b)
Figure 1. Layout of a magnetic field sensor with a polysilicon resonator, which is based on SUMMiT
Figure 1. Layout of a magnetic field sensor with a polysilicon resonator, which is based on SUMMiT V
V process: (a) 3D; and (b) 2D view of the main mechanical components [19]. Reprinted with
process: (a) 3D; and (b) 2D view of the main mechanical components [19]. Reprinted with permission
permission from [19]. Copyright© 2013, Bentham Science Publishers.
from [19]. Copyright©2013, Bentham Science Publishers.
Generally, the fabrication of MEMS magnetic field sensors can be realized using bulk or surface
micromachining
processes. These
processes
use silicon
as their can
main
to its
important
Generally, the fabrication
of MEMS
magnetic
field sensors
bematerial
realizeddue
using
bulk
or surface
mechanical
and
electrical
properties.
For
instance,
silicon
has
minimum
mechanical
hysteresis
and
micromachining processes. These processes use silicon as their main material due to its important
large
rupture
stress
close
to
1
GPa.
In
addition,
silicon
doped
with
phosphorus
or
boron
can
improve
mechanical and electrical properties. For instance, silicon has minimum mechanical hysteresis and
itsrupture
electricalstress
properties.
large
close to 1 GPa. In addition, silicon doped with phosphorus or boron can improve
its electrical properties.
Sensors
Sensors 2016,
2016, 16,
16, 1359
1359
of 25
25
44 of
The bulk micromachining process employs wet and dry etching techniques to fabricate features
The bulk micromachining process employs wet and dry etching techniques to fabricate features
in materials through isotropic and anisotropic etching, respectively [20]. Wet etching is a chemical
in materials through isotropic and anisotropic etching, respectively [20]. Wet etching is a chemical
process that can reach an anisotropic directional etching in crystalline materials (e.g., silicon)
process that can reach an anisotropic directional etching in crystalline materials (e.g., silicon) although,
although, it can get an isotropic etching in an amorphous material (e.g., silicon dioxide). For
it can get an isotropic etching in an amorphous material (e.g., silicon dioxide). For instance, potassium
instance, potassium hydroxide (KOH) is a directional wet etchant for crystalline silicon, which
hydroxide (KOH) is a directional wet etchant for crystalline silicon, which etches 100 times faster on the
etches 100 times faster on the (100) plane than on the (111) plane (see Figure 2). KOH etches very
(100) plane than on the (111) plane (see Figure 2). KOH etches very slowly the silicon nitride or silicon
slowly the silicon nitride or silicon dioxide, which can be used as etch masks. In wet etching, the
dioxide, which can be used as etch masks. In wet etching, the etched depth depends of several variables
etched depth depends of several variables such as etched time, temperature, chemical agitation and
such as etched time, temperature, chemical agitation and solution concentration. The disadvantages of
solution concentration. The disadvantages of the wet etching can be overcome using dry etching
the wet etching can be overcome using dry etching (e.g., plasma etching). Dry etching has advantages
(e.g., plasma etching). Dry etching has advantages such as anisotropic etch, repeatable process and it
such as anisotropic etch, repeatable process and it is easy to start and stop the etched process.
is easy to start and stop the etched process. Plasma etching uses a flux of ions, electrons, radicals and
Plasma etching uses a flux of ions, electrons, radicals and neutral particles to etch the material
neutral particles to etch the material surface. It includes reactive ion etching (RIE), deep reactive ion
surface. It includes reactive ion etching (RIE), deep reactive ion etching (DRIE) and high-density
etching (DRIE) and high-density plasma etching (HDP). Figure 3 shows a SEM image of two
plasma etching (HDP). Figure 3 shows a SEM image of two magnetic field sensors composed by
magnetic field sensors composed by silicon resonators with piezoresistive sensing, which were
silicon resonators with piezoresistive sensing, which were fabricated using a bulk micromachining
fabricated using a bulk micromachining process. These sensors were designed by researchers at
process. These sensors were designed by researchers at Micro and Nanotechnology Research Center
Micro and Nanotechnology Research Center (MICRONA-UV, Boca del Río, Mexico) into
(MICRONA-UV, Boca del Río, Mexico) into collaboration with Microelectronics Institute of Barcelona
collaboration with Microelectronics Institute of Barcelona (IMB-CNM, CSIC, Bellaterra, Spain).
(IMB-CNM, CSIC, Bellaterra, Spain).
Surface micromachining process is a fabrication process of MEMS devices that uses the
Surface micromachining process is a fabrication process of MEMS devices that uses the deposition,
deposition, patterning and etching of different materials layers on a substrate [20]. Commonly, these
patterning and etching of different materials layers on a substrate [20]. Commonly, these layers are
layers are employed as structural and sacrificial layers. The sacrificial layers protect the structural
employed as structural and sacrificial layers. The sacrificial layers protect the structural layers during
layers during the etching process and define the mechanical structure of the MEMS devices. Finally,
the etching process and define the mechanical structure of the MEMS devices. Finally, sacrificial
sacrificial layers are removed using specific chemical substances. Figure 4 shows a polysilicon
layers are removed using specific chemical substances. Figure 4 shows a polysilicon resonator of
resonator of a magnetic field sensor, which is fabricated using a surface micromachining process. It
a magnetic field sensor, which is fabricated using a surface micromachining process. It was designed
was designed by researchers at Micro and Nanotechnology Research Center (MICRONA-UV) into
by researchers at Micro and Nanotechnology Research Center (MICRONA-UV) into collaboration with
collaboration with Sandia National Laboratories.
Sandia National Laboratories.
Figure 2. SEM image of a die reverse-side with two silicon structures which were etched using the
KOH in bulk micromachining process. (Courtesy of A. L. Herrera-May,
Herrera-May, Universidad
UniversidadVeracruzana).
Veracruzana).
Planar fabrication
fabrication
methods
the microelectronic
industry
be used
in surface
methods
of theofmicroelectronic
industry can
be usedcan
in surface
micromachining
micromachining
process.
instance,
this process
tools of the microelectronic
industry the
for
process.
For instance,
thisFor
process
employs
tools ofemploys
the microelectronic
industry for depositing
depositing
thesacrificial
structurallayers,
and sacrificial
as well as
the
patterning
and Thus,
etching
of layers.
Thus,
structural and
as well aslayers,
the patterning
and
etching
of layers.
devices
structures
devices
structures
areetching
obtained
through
etching
of the
structural
layers, which
are anchored
to the
are obtained
through
of the
structural
layers,
which
are anchored
to the substrate
and others
substrate and others structural layers. In the deposition process of structural and sacrificial layers,
Sensors 2016, 16, 1359
5 of 25
Sensors 2016,
2016, 16,
16, 1359
1359
Sensors
of 25
25
55 of
structural layers. In the deposition process of structural and sacrificial layers, residual stress gradients
residual
stress gradients
gradients
can
be generated
generated
on
the structural
structural
layers,
which can
can affect
affect
the
performance
can
be generated
on the can
structural
layers,on
which
can affectlayers,
the performance
of thethe
MEMS
sensors.
residual
stress
be
the
which
performance
of the
the stress
MEMSgradients
sensors. are
These
stress
gradients
areconditions
caused by
bysuch
deposition
conditions
such
as high
high
These
caused
bygradients
deposition
as high conditions
temperature
values
and
of
MEMS
sensors.
These
stress
are
caused
deposition
such
as
temperature
values
and
materials
layers
with
different
thermal
dilation
coefficients.
The
residual
materials
layers
with
different
thermal
dilation
coefficients.
The
residual
stress
gradients
can
be
temperature values and materials layers with different thermal dilation coefficients. The residual
stress
gradients
can
be
decreased
using
post-deposition
annealing
steps.
decreased
using
post-deposition
annealing
steps.
stress gradients can be decreased using post-deposition annealing steps.
Figure 3.
3. SEM
SEM image
image of
of two
two magnetic
magnetic field
field sensors
sensors formed
formed by
by silicon
silicon resonators,
resonators, which
which are
are fabricated
fabricated
Figure
micromachining process.
process. (Courtesy
(Courtesy of
of A.
A. L.
L. Herrera-May,
Herrera-May,Universidad
UniversidadVeracruzana).
Veracruzana).
using
using aa bulk
bulk micromachining
micromachining
process.
(Courtesy
of
A.
L.
Herrera-May,
Universidad
Veracruzana).
Figure 4.
4. SEM
SEM image
image of
of magnetic
magnetic field
field sensor
sensor composed
composed by
by aa polysilicon
polysilicon resonator,
resonator, which
which is
is
Figure
Figure
4. SEM
image of magnetic
field sensor
composed by a polysilicon
resonator, which is fabricated
fabricated using
using aa surface
surface micromachining
micromachining process.
process. (Courtesy of
of A.
A. L.
L. Herrera-May,
Herrera-May, Universidad
Universidad
fabricated
using
a surface micromachining
process. (Courtesy of (Courtesy
A. L. Herrera-May,
Universidad Veracruzana).
Veracruzana).
Veracruzana).
2.1.
Performance
of
MEMS
2.1. Performance
Performance of
of MEMS
MEMS Magnetic
Magnetic Field
Field Sensors
Sensors
2.1.
Magnetic
Field
Sensors
MEMS
magnetic field
field sensors
sensorsuse
useresonators
resonatorstotoincrease
increasetheir
theirsensitivity
sensitivity
due
large
strains
MEMS magnetic
magnetic
due
to to
large
strains
of
MEMS
field sensors
use resonators
to increase their
sensitivity due
to
large
strains
of
of
the
sensor
structure.
The
sensor
structure
operates
at
resonance
through
Lorentz
forces
or
the
sensor
structure.
The
sensor
structure
operates
at
resonance
through
Lorentz
forces
or
the sensor structure. The sensor structure operates at resonance through Lorentz forces or
electrostatic forces
forces whose
whose displacements
displacements are
are related
related to
to the
the magnitude
magnitude of
of the
the applied
applied magnetic
magnetic field.
field.
electrostatic
These
displacements
can
be
detected
using
piezoresistive,
capacitive
or
optical
sensing
techniques.
These displacements can be detected using piezoresistive, capacitive or optical sensing techniques.
For instance,
instance, Figure
Figure 5a,b
5a,b depicts
depicts the
the design
design of
of aa magnetic
magnetic field
field sensor
sensor which
which contains
contains aa resonator
resonator
For
Sensors 2016, 16, 1359
6 of 25
and piezoresistive sensing [21]. This sensor is formed by a rectangular loop of silicon beams, an
6 of 25
a Wheatstone bridge, as shown in Figure 6. This sensor exploits the Lorentz
force (FL) that is generated by the interaction of the electrical current with an external magnetic field
(Bx) parallel forces
to the sensor
electrostatic
whose structure:
displacements are related to the magnitude of the applied magnetic field.
Sensors
2016, 16,
1359 and
aluminum
loop
These displacements can be detected using piezoresistive, capacitive or optical sensing techniques.
(1)
For instance, Figure 5a,b depicts the design of a magnetic field sensor which contains a resonator and
piezoresistive sensing [21]. This sensor is formed by a rectangular loop of silicon beams, an aluminum
withand a Wheatstone bridge, as shown in Figure 6. This sensor exploits the Lorentz force (FL ) that is
loop
generated by the interaction of the electrical current with an external magnetic field (Bx ) parallel to the
sensor structure:
(2)
FL = I Al Bx Lz
(1)
where Lz is width of the rectangular loop, ω and IRMS are circular frequency and root-mean-square
with
√
(RMS) of the sinusoidal electrical current
Al) supplied to the aluminum loop, respectively.
I Al(I=
2IRMS sin(ωt)
(2)
The sensor structure has a deflection and strain generated by the Lorentz force, causing a
where
is width
of the rectangular loop, ω and IRMS are
circular frequency and root-mean-square
changeLz(△R
i) of the initial resistance (Ri) of two p-type
piezoresistors:
(RMS) of the sinusoidal electrical current (IAl ) supplied to the aluminum loop, respectively.
The sensor structure has a deflection and strain generated by the Lorentz force, causing a change
(3)
(4Ri ) of the initial resistance (Ri ) of two p-type piezoresistors:
where πl is longitudinal piezoresistive coefficient,
εl isQlongitudinal
strain of the piezoresistors under
∆Ri = πl Eε
(3)
l T Ri
static load, E is Young’s modulus of the piezoresistor material and QT is total quality factor of the
resonant
structure.
where
π l is
longitudinal piezoresistive coefficient, εl is longitudinal strain of the piezoresistors under
output
voltage modulus
(Vo) of theof
Wheatstone
bridge material
changes due
of the piezoresistors
staticThe
load,
E is Young’s
the piezoresistor
and to
QTvariation
is total quality
factor of the
resistance:
resonant
structure.
The output voltage (Vo ) of the Wheatstone bridge changes due to variation of the
piezoresistors resistance:
(4)
1
Vo = πl Eε l Ri Vi
(4)
2
where Vi is input voltage applied to the Wheatstone
bridge.
whereThe
Vi issensor
input voltage
applied
the Wheatstone
sensitivity
(S) istoobtained
as the bridge.
ratio between the output voltage (Vo) of the
The
sensor
sensitivity
(S)
is
obtained
as
thex):ratio between the output voltage (∆Vo ) of the
Wheatstone bridge to the magnetic field shift (△B
Wheatstone bridge to the magnetic field shift (∆Bx ):
S=
(a)
∆Vo
∆Bx
(5)
(5)
(b)
Figure5.5. 3D
3Dschematic
schematic view
view of
of the
the (a)
(a)upper
upper and
and (b)
(b)bottom
bottomdesign
design of
of magnetic
magnetic field
field sensor,
sensor,which
which
Figure
contains
a
silicon
resonator,
an
aluminum
loop
and
a
Wheatstone
bridge
[21].
Reprinted
with
contains a silicon resonator, an aluminum loop and a Wheatstone bridge [21]. Reprinted with
permission
from
[21].
Copyright©
2011,
Elsevier
B.V.
permission from [21]. Copyright©2011, Elsevier B.V.
Sensors 2016, 16, 1359
Sensors 2016, 16, 1359
7 of 25
7 of 25
Figure 6. 3D
3D schematic
schematicview
viewofofthe
theperformance
performanceofofa aMEMS
MEMSmagnetic
magneticfield
fieldsensor
sensorformed
formed
byby
a
arectangular
rectangularloop
loopofofsilicon
siliconbeams,
beams,an
analuminum
aluminumloop
loopand
andpiezoresistive
piezoresistive sensing
sensing [21]. Reprinted
Reprinted with
permission from [21].
[21]. Copyright©2011,
Copyright© 2011, Elsevier B.V.
B.V.
2.2. Quality Factor
qualityfactor
factor
a resonator
affects
its sensitivity
and resolution.
factor
can be
The quality
of aofresonator
affects
its sensitivity
and resolution.
This factorThis
can be
determined
determined
asthe
thetotal
ratioenergy
of the stored
total energy
stored(E
ins )resonator
(Es) lost
to the
lost
per cycle
C)
as
the ratio of
in resonator
to the energy
perenergy
cycle (E
by(E
the
C ) caused
caused bysources:
the damping sources:
damping
2πEs
Q=
(6)
Ec
For small displacements of the resonator, the quality factor is related with the damping ratio(6)
(ζ):
1
(7)
For small displacements of the resonator, Q
the=quality
factor is related with the damping ratio (ζ):
2ζ
The main damping sources of MEMS resonators are the following: fluid damping, support
(7)
damping and thermoelastic damping. Fluid damping is due to energy loss to a surrounding fluid
and its value is affected by parameters such as the viscosity and pressure of the fluid, resonator
The main damping sources of MEMS resonators are the following: fluid damping, support
size, vibration mode and separation of the resonator with respect to the adjacent surfaces [22].
damping and thermoelastic damping. Fluid damping is due to energy loss to a surrounding fluid
This damping decreases when the fluid pressure is reduced to vacuum, which increases the resonator
and its value is affected by parameters such as the viscosity and pressure of the fluid, resonator size,
motions, the sensitivity and resolution of the sensor. Therefore, a vacuum packaging can improve
vibration mode and separation of the resonator with respect to the adjacent surfaces [22]. This
the performance of magnetic field sensors. The fluid damping is the most dominant source of energy
damping decreases when the fluid pressure is reduced to vacuum, which increases the resonator
dissipation for resonators operating at ambient pressure.
motions, the sensitivity and resolution of the sensor. Therefore, a vacuum packaging can improve
Support damping is generated by the vibration energy dissipation in the supports of resonators.
the performance of magnetic field sensors. The fluid damping is the most dominant source of energy
These supports absorb part of the vibration energy of a resonator, which depends of the support type
dissipation for resonators operating at ambient pressure.
and dimensions, as well as the vibration mode of the sensor structure [23].
Support damping is generated by the vibration energy dissipation in the supports of resonators.
Thermoelastic damping of a resonator is due to the oscillating temperature gradient generated
These supports absorb part of the vibration energy of a resonator, which depends of the support
during the resonator vibration [24]. This temperature gradient causes thermal energy loss that can be
type and dimensions, as well as the vibration mode of the sensor structure [23].
a dominant damping when the resonator operates at vacuum pressure.
Thermoelastic damping of a resonator is due to the oscillating temperature gradient generated
Total quality factor (QT ) of a resonator can be determined considering different damping sources.
during the resonator vibration [24]. This temperature gradient causes thermal energy loss that can be
a dominant damping when the resonator1 operates
1 at 1vacuum
1 pressure.
= can
+ be determined
+
(8)
Total quality factor (QT) of a resonator
considering different damping
QT
Qf
Qs
Qt
sources.
where Qf , Qs , and Qt are quality factors associated with the fluid damping, support damping and
thermoelastic damping, respectively.
(8)
2.3. Sensing Techniques
MEMS magnetic field sensors can employ different sensing techniques such as capacitive, optical,
where Qf, Qs, and Qt are quality factors associated with the fluid damping, support damping and
or piezoresistive. These techniques allow the conversion of magnetic field signals into electrical or
thermoelastic damping, respectively.
Sensors 2016, 16, 1359
8 of 25
2.3. Sensing Techniques
Sensors 2016, 16, 1359
8 of 25
MEMS magnetic field sensors can employ different sensing techniques such as capacitive,
optical, or piezoresistive. These techniques allow the conversion of magnetic field signals into
optical signals,
respectively.
In addition, MEMS
sensorsMEMS
need signal
conditioning
systems
with low
electrical
or optical
signals, respectively.
In addition,
sensors
need signal
conditioning
electronic
noise
parasitic
capacitances.
In the
following paragraphs,
several
examples of
MEMS
systems
with
lowand
electronic
noise
and parasitic
capacitances.
In the following
paragraphs,
several
magneticoffield
sensors
with different
sensing
are discussed.
examples
MEMS
magnetic
field sensors
withtechniques
different sensing
techniques are discussed.
Figure7 7shows
showsthe
theschematic
schematicview
viewofofthe
themain
main
components
a MEMS
magnetic
field
sensor,
Figure
components
ofof
a MEMS
magnetic
field
sensor,
which
uses
a
piezoresistive
sensing
through
a
Wheatstone
bridge
with
four
p-type
piezoresistors
[25].
which uses a piezoresistive
through a Wheatstone bridge with four p-type piezoresistors
3
3
TheThe
sensor
structure
is formed
with awith
silicon
plate (400
150 ×
15 µm
) supported
by fourby
bending
[25].
sensor
structure
is formed
a silicon
plate×(400
× 150
× 15
μm ) supported
four
beams beams
(130 ×(130
12 ×
15×µm
). 3The
plate
interaction between
betweenthe
thesinusoidal
sinusoidal
bending
× 12
15 3μm
). The
plateoscillates
oscillatesdue
dueto
to the
the interaction
electricalcurrent
currentand
andmagnetic
magneticfield
fieldparallel
paralleltotothe
theplate.
plate.This
Thisoscillation
oscillationgenerates
generatesa abending
bendingmotion
motion
electrical
(136.52kHz)
kHz)ofofthe
thebeams,
beams,
which
contain
two
piezoresistors
(40
1 3µm
It alters
the resistance
(136.52
which
contain
two
piezoresistors
(40
× 8××81×
μm
). It3 ).
alters
the resistance
of
of two
piezoresistors,
modifying
the output
voltage
ofWheatstone
the Wheatstone
bridge.
the sensor
has
two
piezoresistors,
modifying
the output
voltage
of the
bridge.
Thus,Thus,
the sensor
has an
an electrical
output
response
for monitoring
magnetic
at atmospheric
pressure.
This has
sensor
electrical
output
response
for monitoring
magnetic
fields fields
at atmospheric
pressure.
This sensor
a
has a quality
ofatmospheric
842 at atmospheric
pressure,
sensitivity
of 403
·T−1 , theoretical
resolution
quality
factor offactor
842 at
pressure,
sensitivity
of 403 mV·
T−1,mV
theoretical
resolution
of 143
1/2 and power
−1/2,nT
ofHz
143
·Hz−1/2 , noise
theoretical
of−1/257.5
·Hz−consumption
consumption
close technical
to 10 mW.
nT·
theoretical
of 57.5noise
nV·Hz
andnV
power
close
to 10 mW. These
These technical
of the are
MEMS
sensorfor
are monitoring
adequate forresidual
monitoring
residual
magnetic
parameters
of theparameters
MEMS sensor
adequate
magnetic
fields
into
fields into ferromagnetic
tubes.this
However,
this sensora registered
a voltage
and a electrical
non-lineal
ferromagnetic
tubes. However,
sensor registered
voltage offset
and aoffset
non-lineal
electrical response.
response.
(b)
(a)
Figure Figure
7. (a) 7.
Schematic
view view
of a ofMEMS
magnetic
field
piezoresistive sensing
sensingthrough
through a
(a) Schematic
a MEMS
magnetic
fieldsensor
sensorwith
with (b)
(b) piezoresistive
Wheatstone
bridge bridge
composed
by four
p-type
piezoresistors
with permission
permissionfrom
from
a Wheatstone
composed
by four
p-type
piezoresistors[25].
[25].Reprinted
Reprinted with
[25].[25].
Copyright©
2015,
IOP
Publishing.
Copyright©2015, IOP Publishing.
Mehdizadeh et al. [26] designed a MEMS magnetic field sensor formed by a dual-plate silicon
Mehdizadeh et al. [26] designed a MEMS magnetic field sensor formed by a dual-plate silicon
resonator (10 μm thickness) with a gold trace (10 μm width and 200 nm thickness) on one of its two
resonator (10 µm thickness) with a gold trace (10 µm width and 200 nm thickness) on one of its
plates (see Figure 8). Two narrow beams in the middle of the resonator connecting the two silicon
two plates (see Figure 8). Two narrow beams in the middle of the resonator connecting the two
plates have behave as piezoresistors. It is due to the periodic tensile and compressive stress when the
silicon plates have behave as piezoresistors. It is due to the periodic tensile and compressive stress
resonator oscillates in-plane vibration mode. This Lorentz force-based sensor is fabricated using a
when the resonator oscillates in-plane vibration mode. This Lorentz force-based sensor is fabricated
low-resistivity n-type silicon-on-insulator (SOI) substrate. The quality factor of this resonator has
using a low-resistivity n-type silicon-on-insulator (SOI) substrate. The quality factor of this resonator
amplification from 1140 to 16,900 at atmospheric pressure. This sensor improves its sensitivity by
has amplification from 1140 to 16,900 at atmospheric pressure. This sensor improves its sensitivity
increasing the resonator vibration amplitude. The sensor has a sensitivity of 262 mV·T−1 in−1air, a
by increasing the resonator vibration amplitude. The sensor has a sensitivity of 262 mV·T in air,
resonant frequency of 2.6 MHz and a quality factor of 16,900. Nevertheless, the MEMS sensor
a resonant frequency of 2.6 MHz and a quality factor of 16,900. Nevertheless, the MEMS sensor requires
requires more studies of the effects of temperature on its performance.
more studies of the effects of temperature on its performance.
Sensors 2016, 16, 1359
9 of 25
Sensors 2016, 16, 1359
9 of 25
(a)
(b)
Figure8.8.SEM
SEMimage
imageofofthe
the(a)
(a)main
mainelements
elementsofofa aMEMS
MEMSmagnetic
magneticfield
fieldsensor
sensorwith
withpiezoresistive
piezoresistive
Figure
readout,
which
is
composed
by
a
dual-plate
silicon
resonator
with
a
gold
trace
and
piezoresistors;
(b)
readout, which is composed by a dual-plate silicon resonator with a gold trace and piezoresistors;
Electrical
connections
of
the
magnetic
field
sensor
[26].
Reprinted
with
permission
from
[26].
(b) Electrical connections of the magnetic field sensor [26]. Reprinted with permission from [26].
Copyright© 2014,IEEE.
IEEE.
Copyright©2014,
A MEMS magnetic field device (see Figure 9) with a simple resonator and linear electrical
A MEMS magnetic field device (see Figure 9) with a simple resonator and linear electrical response
response was presented by Herrera-May et al. [27]. It is formed by a perforate plate (472 × 300 ×3 15
was 3presented by Herrera-May et al. [27]. 3 It is formed by a perforate plate (4723 × 300 × 15 µm ),
μm ), four flexural beams (18 × 15 × 15 μm ), two support beams (60 × 36 × 15 μm ) and a Wheatstone
four flexural beams (18 × 15 × 15 µm3 ), two support beams (60 × 36 × 15 µm3 ) and a Wheatstone
bridge with four p-type piezoresistors. The device exploits the Lorentz force and operates at its
bridge with four p-type piezoresistors. The device exploits the Lorentz force and operates at its seesaw
seesaw resonant frequency (100.7 kHz) without vacuum packaging. A standard bulk
resonant frequency (100.7 kHz) without vacuum packaging. A standard bulk micromachining process
micromachining process and SOI wafers are used to fabricate the device, as shown in Figure 10. The
and SOI wafers are used to fabricate the device, as shown in Figure 10. The dynamic range of the
dynamic range of the device can be adjusted by modifying the excitation electrical current, keeping
device can be adjusted by modifying the excitation electrical current, keeping its linear
electrical
its linear electrical response. It has a quality factor of 419.6, a sensitivity of 230 mV·T−1, a resolution of
response. It has a quality factor of 419.6, a sensitivity of 230 mV·T−1 , a resolution of 2.5 µT and
2.5 μT and a power consumption of 12 mW. Due to the advantages of this sensor, it could be
a power consumption of 12 mW. Due to the advantages of this sensor, it could be employed in
employed in applications of non-destructive magnetic testing to detect flaws and corrosion of
applications of non-destructive magnetic testing to detect flaws and corrosion of ferromagnetic
ferromagnetic materials. For this application, the sensor needs reliability studies of its behavior
materials. For this application, the sensor needs reliability studies of its behavior under different
under different conditions of temperature, moisture, and fatigue.
conditions of temperature, moisture, and fatigue.
Figure 11 depicts a schematic view of a MEMS magnetic field sensor with capacitive readout
Figure 11 depicts a schematic view of a MEMS magnetic field sensor with capacitive readout
technique [28]. This sensor detects magnetic field with orthogonal direction (z-axis along) to surface
technique [28]. This sensor detects magnetic field with orthogonal direction (z-axis along) to surface of
of the resonant structure. It consists of a set of fixed stators and a shuttle suspended with two thin
the resonant structure. It consists of a set of fixed stators and a shuttle suspended with two thin beams
beams (see Figure 11), which forms two differential parallel-plate sensing capacitors C1 and C2. A
(see Figure 11), which forms two differential parallel-plate sensing capacitors C1 and C2 . A Lorentz
Lorentz force is generated on two thin beams caused by the interaction between the magnetic field
force is generated on two thin beams caused by the interaction between the magnetic field and
and ac electrical current flowing through the beams with the sensor resonant frequency. This force
ac electrical current flowing through the beams with the sensor resonant frequency. This force has
has an orthogonal direction to the plane of both magnetic field and ac current, causing a
an orthogonal direction to the plane of both magnetic field and ac current, causing a displacement of the
displacement of the beams and parallel plates. This displacement is detected through the differential
beams and parallel plates. This displacement is detected through the differential capacitance variation
capacitance variation between the parallel plates and fixed stators (see Figure 12). The sensor
between the parallel plates and fixed stators (see Figure 12). The sensor sensitivity is measured as the
sensitivity is measured as the differential capacitance shift per variation of magnetic field. This
differential capacitance shift per variation of magnetic
field. This sensor has an overall sensitivity of
sensor has
an overall sensitivity of 150 μV·μT−1 at 250 μA of peak driving current,−a1/2
theoretical noise
−
1
150 µV·µT at 250
of peak driving current, a −1theoretical
noise of 557.2 µV·Hz
, a resolution
−1/2,µA
−1/2, a quality
of 557.2 μV·
Hz
a
resolution
of
520
nT·
mA
·
Hz
factor
around
328, a resonant
of 520 nT·mA−1 ·Hz−1/2 , a quality factor around 328, a resonant frequency of 28.3 kHz and a typical
frequency of 28.3 kHz and a typical industrial packaging. The technical characteristics of this sensor
industrial packaging. The technical characteristics of this sensor are suitable for consumer applications
are suitable for consumer applications (e.g., digital compass, dead reckoning, heading, map
(e.g., digital compass, dead reckoning, heading, map rotation), although this sensor only detects the
rotation), although this sensor only detects the components of the magnetic field in one direction
components of the magnetic field in one direction and its performance depends on the temperature.
and its performance depends on the temperature. This sensor could include a temperature device,
This sensor could include a temperature device, embedded on the same MEMS readout electronic,
embedded on the same MEMS readout electronic, for post-acquisition compensation of temperature
for post-acquisition compensation of temperature alterations. Therefore, this sensor requires initial
alterations. Therefore, this sensor requires initial calibration and temperature compensation.
calibration and temperature compensation.
Sensors 2016, 16, 1359
Sensors 2016, 16, 1359
Sensors 2016,
2016, 16,
16, 1359
1359
Sensors
10 of 25
10 of 25
10 of
of 25
25
10
Figure
9. Schematic
Figure
9.
Schematic view
view of
of the
the main
main components
components of
of aaa MEMS
MEMS magnetic
magnetic field
field device
device designed
designed by
by
Figure 9.
9. Schematic
Schematic
view
of
the
main
components
of
MEMS
magnetic
field
device
designed
by
Figure
view
of
the
main
components
of
a MEMS
magnetic
field
device
designed
by
Herrera-May
et al.
al. [27].
[27]. Reprinted
with
permission from
from [27].
[27]. Copyright©2015,
Copyright© 2015, Elsevier
Elsevier B.V.
B.V.
Herrera-May
et
Reprinted
with
permission
Herrera-May et
et al.
al. [27].
[27]. Reprinted
Reprinted with
with permission
permission from
from [27].
[27]. Copyright©
Copyright© 2015,
2015, Elsevier
Elsevier B.V.
B.V.
Herrera-May
(a)
(a)
(a)
(b)
(b)
(b)
Figure 10. SEM image of a MEMS magnetic field device with piezoresistive sensing: (a) Silicon
Figure 10.
10. SEM
SEM
image
of
MEMS magnetic
magnetic field
field device
device with piezoresistive
piezoresistive sensing:
sensing: (a)
(a) Silicon
Silicon
Figure
image
aaa MEMS
SEM
image of
ofloop;
MEMS
magnetic
resonator
and
aluminum
(b) Wheatstone
bridge with with
four piezoresistors [27].
Reprinted with
resonator and
and aluminum
aluminum loop;
loop; (b)
(b) Wheatstone
Wheatstone bridge
bridge with
with four
four piezoresistors
piezoresistors [27].
[27]. Reprinted
Reprinted with
with
resonator
resonator
and
aluminum
loop;
Reprinted
with
permission
from
[27]. Copyright©
2015, Elsevier B.V.
permission from
from [27].
[27]. Copyright©
Copyright©
2015,
Elsevier
B.V.
permission
2015,
Elsevier
B.V.
Copyright©2015,
B.V.
Figure 11. Schematic view of a MEMS magnetic field sensor formed with parallel plates, fixed
Figure 11. Schematic
Schematic view
view
of
MEMS
magnetic
field
sensor
formed with
with parallel
parallel plates,
plates, fixed
fixed
Figure
magnetic
field
sensor
formed
view of
of aaabyMEMS
MEMS
magnetic
fieldsensor
sensoruses
formed
with
parallel
plates,
fixed
stators, 11.
and Schematic
a shuttle supported
two thin
beams. This
the Lorentz
force, which
causes
stators, and
and aa shuttle
shuttle supported
supported by
by two
two thin
thin beams.
beams. This
sensor
uses
the
Lorentz
force,
which causes
causes
stators,
sensor
uses
force,
which
This
sensor
uses the
the Lorentz
Lorentz
force,
which
causes
a displacement
of itssupported
resonant structure
measuredThis
through
differential
capacitors
[28].
Reprinted
displacementof
ofits
itsresonant
resonant
structure
measured
through
differential
capacitors
[28].
Reprinted
aa displacement
displacement
of
its
resonant
structure
measured
through
differential
capacitors
[28].
Reprinted
structure 2013,
measured
with permission from [28]. Copyright©
IEEE.through differential capacitors [28]. Reprinted with
with permission
permission
from
[28]. Copyright©
Copyright© 2013,
2013,
IEEE.
with
[28].
permission
from from
[28]. Copyright©2013,
IEEE.IEEE.
Sensors 2016, 16, 1359
Sensors 2016, 16, 1359
11 of 25
11 of 25
Figure
of the
mainmain
components
of a MEMS
magneticmagnetic
field sensor
with
capacitive
Figure 12.
12.Microphotography
Microphotography
of the
components
of a MEMS
field
sensor
with
sensing
[28].
Reprinted
permission
from [28]. Copyright©2013,
IEEE.2013, IEEE.
capacitive
sensing
[28]. with
Reprinted
with permission
from [28]. Copyright©
Zhang et
et al.
Zhang
al. [29]
[29] developed
developed aa silicon
silicon micromechanical
micromechanicalmagnetic
magneticfield
fieldsensor
sensorbased
basedonona
tuning
fork
(DETF)
resonator,
as as
shown
in Figure
13. 13.
ThisThis
silicon
resonator
has two
adouble-ended
double-ended
tuning
fork
(DETF)
resonator,
shown
in Figure
silicon
resonator
has
2) clamped
2
parallel
beams
(600
×
8
μm
to
two
doubly
fixed
crossbars
and
two
sets
of
comb
drive
two parallel beams (600 × 8 µm ) clamped to two doubly fixed crossbars and two sets of comb drive
electrodes joined
joined to
to each
each parallel
parallel beam.
beam. The
The first
first set
set of
of comb
comb drive
drive electrodes
electrodes operates
operates as
as actuation
actuation
electrodes
mechanismand
andthe
thesecond
second
of electrodes
a sensing
mechanism.
The DEFT
resonator
is
mechanism
setset
of electrodes
actsacts
as a as
sensing
mechanism.
The DEFT
resonator
is driven
driven
using
an
electrostatic
force
that
activates
its
in-plane
(46.8
kHz)
and
anti-phase
(49.3
kHz)
using an electrostatic force that activates its in-plane (46.8 kHz) and anti-phase (49.3 kHz) vibration
vibration
modes13
(Figures
13 This
and 14).
This
sensor measures
the resonant
shift
the
modes
(Figures
and 14).
sensor
measures
the resonant
frequencyfrequency
shift using
theusing
Lorentz
Lorentz
force.
This
force
is
generated
by
the
interaction
of
an
out-of-plane
magnetic
field
and
dc
force. This force is generated by the interaction of an out-of-plane magnetic field and dc electrical
electrical
current
flowing
through
the
two
crossbars.
The
Lorentz
force
modifies
the
stiffness
of
the
current flowing through the two crossbars. The Lorentz force modifies the stiffness of the two parallel
two parallel
which
resonant
function
ofmagnetic
the applied
magnetic
field.
beams,
whichbeams,
modifies
the modifies
resonant the
frequency
infrequency
function ofinthe
applied
field.
This sensor
This
sensor
was
fabricated
using
SOI
wafers
during
a
standard
bulk
micromachining
process.
Using
was fabricated using SOI wafers during a standard bulk micromachining process. Using a resonator
a resonator
of 10-thickness,
field sensor
reaches
of and
215.74
ppm/T
and
of
10-thickness,
the magnetic the
fieldmagnetic
sensor reaches
sensitivities
of sensitivities
215.74 ppm/T
203.71
ppm/T
203.71
ppm/T for and
the in-phase
anti-phase
and in-phase
vibration mode,
respectively.
anti-phase
and
for
the anti-phase
vibration
mode, respectively.
For anti-phase
andFor
in-phase
vibration
in-phase
vibration
mode,
the
resonator
has
a
quality
factor
of
100,000
and
42,000,
respectively.
mode, the resonator has a quality factor of 100,000 and 42,000, respectively. However, the dc current
However,tothe
currentincreases
suppliedthe
to crossbars
the crossbars
increasescausing
the crossbars
temperature, frequency
causing a
supplied
thedc
crossbars
temperature,
a thermally-induced
thermally-induced
frequency
shift.
This
effect
is
minimized
by
reducing
the
resistance
across
the
shift. This effect is minimized by reducing the resistance across the crossbars through depositing
crossbars
through
depositing
a
metal
stack
of
chromium
and
gold
along
the
crossbars.
This
sensor
a metal stack of chromium and gold along the crossbars. This sensor needs a vacuum packaging and
needsresearches
a vacuum on
packaging
and moreofresearches
the dependence
the sensor
performance
more
the dependence
the sensoronperformance
withof
respect
to the
Joule effect with
and
respect
to
the
Joule
effect
and
damping
sources.
damping sources.
Sensors 2016, 16, 1359
Sensors 2016, 16, 1359
12 of 25
12 of 25
Figure 13.
13. Schematic
DETF silicon
silicon resonator,
resonator, including
including the
the
Figure
Schematic of
of aa magnetic
magnetic field
field sensor
sensor formed
formed by
by aa DETF
biasing configuration
configuration with
with aa transimpedance
transimpedance amplifier
amplifier (TIA)
(TIA) at
at the
the sensing
sensing port.
port. The
right side
side
biasing
The right
depicts the
the anti-phase
anti-phasevibration
vibrationmode
modeofofthe
theDETF
DETF
resonator
and
a cross
section
schematic
view
of
depicts
resonator
and
a cross
section
schematic
view
of the
the
sensor
[29].
Reprinted
with
permission
from
[29].
Copyright©
2014,
Elsevier
B.V.
sensor [29]. Reprinted with permission from [29]. Copyright©2014, Elsevier B.V.
Figure
Figure 14.
14. Schematic of a magnetic field sensor formed by a DETF silicon resonator, which considers
the
transimpedance amplifier
amplifier (TIA)
(TIA) at
at the
the sensing
sensing port.
port. The right
the bias
bias configuration
configuration with
with aa transimpedance
right side
side
shows
Reprinted with
with permission
permission from
from [29].
[29].
shows the
the in-phase
in-phase vibration mode of the DETF resonator [29]. Reprinted
Copyright©2014,
B.V.
Copyright© 2014, Elsevier
B.V.
Elsevier
Li etetal.al.[30]
designed
a magnetic
field sensor
composed
of a flexural
resonator
× 680
Li
[30]
designed
a magnetic
field sensor
composed
of abeam
flexural
beam(1200
resonator
3), which is
3
×
40
μm
then
coupled
to
current-carrying
silicon
beams
through
a
microleverage
(1200 × 680 × 40 µm ), which is then coupled to current-carrying silicon beams through
This
resonator This
usesresonator
electrostatic
and
capacitive
through
comb
amechanism.
microleverage
mechanism.
usesactuation
electrostatic
actuation
and sensing
capacitive
sensing30
through
fingers
each side
of the
flexural
as beam,
shownas
inshown
Figure in
15.Figure
The sensor
detects
thedetects
magnetic
30
combonfingers
on each
side
of thebeam,
flexural
15. The
sensor
the
field
using
the
resonant
frequency
shift
due
to
the
Lorentz
force,
which
operates
as
axial
load
the
magnetic field using the resonant frequency shift due to the Lorentz force, which operates ason
axial
resonator
(Figure
16). The
microleverage
mechanism amplifies
the tension
produced
by the
Lorentz
load
on the
resonator
(Figure
16). The microleverage
mechanism
amplifies
the tension
produced
force,
increasing
the
sensor’s
sensitivity
by
a
factor
of
42
with
respect
to
the
same
design
without
this
by the Lorentz force, increasing the sensor’s sensitivity by a factor of 42 with respect to the same
mechanism.
The
sensor
uses
vacuum
packaging
obtained
by
using
eutetic
bonding
between
the
two
design without this mechanism. The sensor uses vacuum packaging obtained by using eutetic
wafers. The
sensorthe
obtains
sensitivity
6687 ppm/(mA·
a noise floor
of 0.5
ppm·Hz−1/2
, a aquality
bonding
between
two awafers.
Theofsensor
obtains a T),
sensitivity
of 6687
ppm/(mA
·T),
noise
−
1/2
factor
of
540
and
a
resonant
frequency
of
21.9
kHz.
The
sensor’s
sensitivity
improves
when
the
floor of 0.5 ppm·Hz
, a quality factor of 540 and a resonant frequency of 21.9 kHz. The sensor’s
quality
factor
increases.
With
this,
the
sensor
could
be
used
for
compass
applications.
This
sensor
sensitivity improves when the quality factor increases. With this, the sensor could be used for compass
uses a large silicon
beam uses
(500 a× large
40 × silicon
3 μm3) beam
subject
to ×
flexural
mechanical
applications.
This sensor
(500
40 × 3loads,
µm3 ) which
subjectneeds
to flexural
loads,
reliability
testing.
which needs mechanical reliability testing.
Sensors
Sensors 2016,
2016, 16,
16, 1359
1359
Sensors 2016, 16, 1359
13
13 of
of 25
25
13 of 25
Figure 15. SEM image of magnetic field sensor (left) and its simulated vibration mode (right) [30].
Figure 15.
15. SEM image of magnetic field sensor (left) and its simulated vibration mode
Figure
mode (right)
(right) [30].
[30].
Reprinted with permission from [30]. Copyright© 2015, IEEE.
Reprinted with
with permission
permission from
from [30].
[30]. Copyright©2015,
Copyright© 2015, IEEE.
IEEE.
Reprinted
Figure 16. Operation principle of a magnetic field sensor with microleverage mechanism. A magnetic
Figure 16. Operation principle of a magnetic field sensor with microleverage mechanism. A magnetic
Figure
Operation
principle
a magnetic
field (I
sensor
with microleverage
mechanism.
A magnetic
field
(B)16.
interacts
with
the DC of
excitation
current
) to generate
a Lorentz force,
which operates
as
field (B) interacts with the DC excitation current (IBB) to generate a Lorentz force, which operates as
field
(B)
interacts
with
the
DC
excitation
current
(I
B
)
to
generate
a
Lorentz
force,
which
operates
as
axial load on the flexural beam resonator. This force is mechanically amplified by the microleverage
axial load on the flexural beam resonator. This force is mechanically amplified by the microleverage
axial
load
on
the
flexural
beam
resonator.
This
force
is
mechanically
amplified
by
the
microleverage
mechanism [30]. Reprinted with permission from [30]. Copyright©2015, IEEE.
mechanism [30]. Reprinted with permission from [30]. Copyright© 2015, IEEE.
mechanism [30]. Reprinted with permission from [30]. Copyright© 2015, IEEE.
Aditi and
fabricated
a MEMS
magnetic
field sensor
(see Figure
17) by anodic
andGopal
Gopal[31]
[31]
fabricated
a MEMS
magnetic
field sensor
(see Figure
17) bybonding
anodic
Aditi and Gopal [31] fabricated a MEMS magnetic field sensor (see Figure 17) by anodic
technique
using SOIusing
and glass
Thiswafers.
sensor This
has asensor
xylophone
of highly
doped
silicon
bonding technique
SOI wafers.
and glass
has aresonator
xylophone
resonator
of highly
bonding technique using SOI and glass wafers. This sensor has a xylophone resonator of highly
without
a metalwithout
top electrode.
fabrication
has the
advantages
a low temperature
doped silicon
a metalThe
topdevice
electrode.
The device
fabrication
hasfollowing:
the advantages
following: a
doped◦silicon without a metal top electrode. The device fabrication has the advantages following: a
(low
≤400
C) process,
reliable,
repeatable,
reduced
lithography
steps
and the ability
control
the gap
temperature
(≤400
°C) process,
reliable,
repeatable,
reduced
lithography
stepsto
and
the ability
to
low temperature (≤400 °C) process, reliable, repeatable, reduced lithography steps and the ability to
between
thegap
electrodes.
addition,
the In
device
uses athe
vacuum
(1200packaging
Pa) at die level
control the
betweenIn
the
electrodes.
addition,
device packaging
uses a vacuum
(1200which
Pa) at
control the gap between the electrodes. In addition, the device uses a vacuum packaging (1200 Pa) at
is
through
an anodic
bonding
process.bonding
The xylophone
the Lorentz
forcethe
to Lorentz
operate
dieobtained
level which
is obtained
through
an anodic
process. exploits
The xylophone
exploits
die level which is obtained through an anodic bonding process. The xylophone exploits the Lorentz
its
first
resonant
mode
(108.75
kHz)
with
a
quality
factor
of
180.
The
xylophone
is
electromagnetically
force to operate its first resonant mode (108.75 kHz) with a quality factor of 180. The xylophone is
force to operate its first resonant mode (108.75 kHz) with a quality factor of 180. The xylophone is
actuated,
causing displacements
that aredisplacements
electrostatically
sensed
by capacitive method
18).
electromagnetically
actuated, causing
that
are electrostatically
sensed(see
by Figure
capacitive
electromagnetically actuated, causing displacements that are electrostatically sensed by capacitive
The
device
behaves
as
a
parallel
plate
capacitor,
in
which
a
capacitive
sensing
circuit
converts
the
method (see Figure 18). The device behaves as a parallel plate capacitor, in which a capacitive
method (see Figure 18). The device behaves as a parallel plate capacitor, in which a capacitive
capacitance
shift
to an electrical
signal. Itshift
has to
a power
consumption
ofhas
0.45amW
andconsumption
a resolution of
sensing circuit
converts
the capacitance
an electrical
signal. It
power
sensing circuit
the capacitance shift to an electrical signal. It has a power consumption of
−1/2 . converts
215
·Hzand
sensor can
be used
for−1/2
non-destructive
magnetic
testing
of
ferromagnetic
materials.
0.45nT
mW
aThis
resolution
of 215
nT·Hz
.
This
sensor
can
be
used
for
non-destructive
magnetic
0.45 mW and a resolution of 215 nT·Hz−1/2. This sensor can be used for non-destructive magnetic
In
addition,
with
an
improvement
in
the
vacuum
pressure
(about
10
Pa),
this
sensor
could
be
employed
testing of ferromagnetic materials. In addition, with an improvement in the vacuum pressure (about
testing of ferromagnetic materials. In addition, with an improvement in the vacuum pressure (about
as
compass
in electronic
andasgadgets.
Forin
a constant
field,
the device
10 aPa),
this sensor
could bedevices
employed
a compass
electronicmagnetic
devices and
gadgets.
For registered
a constant
10 Pa), this sensor could be employed as a compass in electronic devices and gadgets. For a constant
amagnetic
non-linear
displacement
when
the input displacement
current magnitude
overcomes
µA.current
field,
the devicevariation
registered
a non-linear
variation
when the 400
input
magnetic field, the device registered a non-linear displacement variation when the input current
magnitude overcomes the 400 μA.
magnitude overcomes the 400 μA.
Sensors 2016, 16, 1359
Sensors
Sensors2016,
2016,16,
16,1359
1359
14 of 25
14
14of
of25
25
Figure
17.
xylophone
beams,
Figure 17.
17. SEM
SEM image
image of
of aaa silicon
silicon xylophone
xylophone supported
supported by
by four
four beams,
beams, which
which take
take advantage
advantage of
of
Figure
SEM
image
of
silicon
supported
by
four
which
take
advantage
of
capacitive
sensing
to
detect
magnetic
field
[31].
Reprinted
with
permission
from
[31].
capacitivesensing
sensing
to detect
magnetic
[31]. with
Reprinted
withfrom
permission
from [31].
capacitive
to detect
magnetic
field [31].field
Reprinted
permission
[31]. Copyright©2016,
Copyright©
2016,
International
Copyright©
2016,Springer
Springer
International
PublishingAG.
AG.
Springer
International
Publishing
AG. Publishing
(a)
(a)
(b)
(b)
Figure
Figure 18.
18. Schematic
Schematic of
of the:
the: (a)
(a) operation
operation principle
principle of
of aa xylophone
xylophone resonator;
resonator; and
and (b)
(b) its
its electrical
electrical
Figure 18. Schematic of the: (a) operation principle of a xylophone resonator; and (b) its electrical
connections
for
capacitive
sensing
[31].
Reprinted
with
permission
from
[31].
Copyright©
2016,
connections
for
capacitive
sensing
[31].
Reprinted
with
permission
from
[31].
Copyright©
2016,
connections for capacitive sensing [31]. Reprinted with permission from [31]. Copyright©2016, Springer
Springer
International
Publishing
AG.
Springer
International
Publishing
AG.
International Publishing AG.
Vasquez
Vasquez and
and Judy
Judy [32]
[32] designed
designed aa zero-power
zero-power magnetic
magnetic field
field sensor
sensor that
that is
is integrated
integrated with
with aa
Vasquez
and
Judy
[32]
designed
a
zero-power
magnetic
field
sensor
that
is
integrated
with
micromachined
micromachined corner-cube
corner-cube reflector
reflector (CCR),
(CCR), aa commercially
commercially available
available diode
diode laser
laser and
and aa
a micromachined
corner-cube
reflector
(CCR),The
a commercially
available diode
laser and a photodetector
photodetector
photodetector array,
array, as
as shown
shown in
in Figure
Figure 19.
19. The sensor
sensor is
is composed
composed of
of aa torsional
torsional polysilicon
polysilicon beam
beam
array,
as
shown
in
Figure
19.
The
sensor
is
composed
of
a
torsional
polysilicon
beamplate.
joined to
joined
joined to
to aa polysilicon
polysilicon plate
plate and
and aa permanent
permanent magnet
magnet (CoNi
(CoNi layer)
layer) is
is deposited
deposited on
on the
the plate. This
This
a polysilicon
plate around
and a permanent
magnet
(CoNi
layer)
is deposited
oncomposed
the plate.by
This
magnet
can
magnet
can
rotate
the
beam
axis.
On
the
other
hand,
the
CCR
is
an
orthogonal
magnet can rotate around the beam axis. On the other hand, the CCR is composed by an orthogonal
rotate of
around
the beam
axis. On
the other
hand,
the CCR
is composed
by
an
orthogonal
array of
two
array
two
fixed
polysilicon
mirrors
and
a
flexible
mirror
connected
to
the
torsional
beam.
Thus,
array of two fixed polysilicon mirrors and a flexible mirror connected to the torsional beam. Thus,
fixed
polysilicon mirrors
and a flexible
mirror connected
to the torsional
beam. CCR
Thus, the
flexible
the
the flexible
flexible mirror
mirror is
is coupled
coupled to
to the
the magnet
magnet rotation,
rotation, as
as shown
shown in
in Figure
Figure 20.
20. The
The CCR is
is fabricated
fabricated
mirrormulti-user
is coupled to the magnet
rotation, as shown
in Figure
20. The CCRfield
is fabricated
using multi-user
using
using multi-user MEMS
MEMS processes
processes (MUMPs)
(MUMPs) [33].
[33]. When
When the
the magnetic
magnetic field is
is zero,
zero, the
the three
three mirrors
mirrors
2)
2) of
MEMS
processes
(MUMPs)
[33].
When
the
magnetic
field
is
zero,
the
three
mirrors
(500
× 500 µm
(500
×
500
μm
the
CCR
are
perpendicular
to
one
another.
An
alteration
of
the
magnetic
(500 × 500 μm2) of the CCR are perpendicular to one another. An alteration of the magnetic field
field
of the CCRa are
perpendicular
to one another.
An alteration
of theproportional
magnetic field produces
a rotation
produces
produces a rotation
rotation of
of the
the magnet
magnet and
and flexible
flexible mirror,
mirror, which
which is
is proportional to
to the
the magnetic
magnetic field.
field.
of the amagnet
and flexible
mirror,
which is proportional
to thetwo
magnetic field.
Then, a diode laser
is
Then,
Then, a diode
diode laser
laser is
is used
used to
to interrogate
interrogate the
the CCR,
CCR, splitting
splitting in
in two beams
beams the
the reflected
reflected optical
optical beam.
beam.
used
to
interrogate
the
CCR,
splitting
in
two
beams
the
reflected
optical
beam.
The
displacements
of
The
The displacements
displacements of
of these
these optical
optical beams
beams are
are measured
measured through
through aa photodetector
photodetector array.
array. This
This sensor
sensor
these optical
beams power
are measured
through and
a photodetector
array. This sensor
does
not
require power
does
not
require
consumption
it
can
continuously
operate
in
extremely
does not require power consumption and it can continuously operate in extremely harsh
harsh
consumption and
it as
canindustrial,
continuously
operateand
in extremely
harsh environments
such as
industrial,
environments
aerospace
the
sector.
can
detect
environments such
such
as industrial,
aerospace
and
the automotive
automotive
sector. This
This sensor
sensor
can
detect aa
aerospace field
automotive
sector.
sensor
detect a magnetic
from
1030 µT to 7540 µT
magnetic
from
1030
7540
μT
an
uncertainty
of
at
optical-interrogation
magnetic and
fieldthe
from
1030 μT
μT to
to
7540This
μT with
with
ancan
uncertainty
of 113
113 μT
μTfield
at 1-m
1-m
optical-interrogation
with
anTo
uncertainty
113sensor’s
µT at 1-m
optical-interrogation
range.
To improve
thebesensor’s
performance
range.
improve
performance
the
curvature
could
and
range.
To
improveofthe
the
sensor’s
performance
the mirror
mirror
curvature
could
be decreased
decreased
and the
the
the
mirror
curvature
could
be
decreased
and
the
mirror’s
size
and
magnet
volume
increased,
as
well as
mirror’s
size
and
magnet
volume
increased,
as
well
as
attaching
the
mirrors
directly
to
the
magnet.
mirror’s size and magnet volume increased, as well as attaching the mirrors directly to the magnet.
attaching
thehas
mirrors
directlyapplication
to the magnet.
This sensor
has asystems
potential
application
in
wireless
This
aa potential
in
sensing
that
operate
hostile
This sensor
sensor
has
potential
application
in wireless
wireless
sensing
systems
that
operate in
in harsh
harsh or
orsensing
hostile
systems
that
operate
in
harsh
or
hostile
locations
that
do
not
need
to
provide
sensor-node
energy.
locations
that
do
not
need
to
provide
sensor-node
energy.
However,
more
studies
on
the
effects
locations that do not need to provide sensor-node energy. However, more studies on the effects of
of
However,
studies
the effects
of etch
on the sensor sensitivity should be performed.
etch
on
sensor
sensitivity
should
be
performed.
etch holes
holesmore
on the
the
sensoron
sensitivity
should
beholes
performed.
Sensors 2016, 16, 1359
15 of 25
Sensors 2016, 16, 1359
Sensors 2016, 16, 1359
15 of 25
15 of 25
(a)
(a)
(b)
(b)
Figure 19. SEM image of a MEMS magnetic field sensor integrated with a CCR: (a) before; (b) after
Figure
image
magnetic
field
sensor
integrated
with aa CCR:
CCR: (a)
(a) before;
before; (b)
(b) after
after
Figure19.
19.SEM
SEMReprinted
imageofofawith
aMEMS
MEMS
magnetic
field
sensor
integrated
assembly
[32].
permission
from
[32].
Copyright©
2007,with
IEEE.
assembly
assembly[32].
[32].Reprinted
Reprintedwith
withpermission
permissionfrom
from[32].
[32]. Copyright©2007,
Copyright© 2007, IEEE.
IEEE.
(a)
(a)
(b)
(b)
Figure 20. Schematic of a MEMS magnetic field sensor composed of a CCR: (a) without; (b) with an
Figure20.
20.
Schematic
of In
magnetic
sensor
composed
a CCR:
(a)
without;
(b) torsion
with
an
external
magnetic
field.
addition,
a close field
up
view
of the
couplingofbetween
the(a)
mirror
and
Figure
Schematic
of
aa MEMS
MEMS
magnetic
field
sensor
composed
of
a CCR:
without;
(b)
with
external
magnetic
field.
In
addition,
a
close
up
view
of
the
coupling
between
the
mirror
and
torsion
beam
is
shown
[32].
Reprinted
with
permission
from
[32].
Copyright©
2007,
IEEE.
an external magnetic field. In addition, a close up view of the coupling between the mirror and torsion
beamisisshown
shown[32].
[32].Reprinted
Reprintedwith
withpermission
permissionfrom
from[32].
[32]. Copyright©2007,
Copyright© 2007, IEEE.
IEEE.
beam
Park et al. [34] designed a magnetic field sensor formed by a silicon resonator and compact laser
Park et system.
al. [34] designed
a magnetic
field sensor formed
by a diode
siliconfor
resonator
and compact
laser
positioning
This system
has a photodetector
and laser
monitoring
the angular
Park
et
al.
[34]
designed
a
magnetic
field
sensor
formed
by
a
silicon
resonator
and
compact
laser
positioning system.
This system
hasmirror
a photodetector
diode for
monitoringofthe
displacement
of a current
biased
membrane.and
Thelaser
resonator
is composed
a angular
silicon
positioning
system.
This
system has
a photodetector
and
laser
diode for
thea 3angular
displacement
of ×a 3000
current
mirror
membrane.
The
resonator
is ×monitoring
composed
membrane
(3000
× 12biased
μm3) coated
with
an aluminum
layer (2500
2500 × 0.8ofμm
).silicon
The
displacement
of
a
current
biased
mirror
membrane.
The
resonator
is
composed
of
a
silicon
membrane
3) coated with an aluminum layer
3). The
3
membrane is
(3000
×
3000
×
12
μm
(2500
×
2500
×
0.8
μm
supported
by two torsional springs (2100 × 100 × 12 μm ), in which an
aluminum wire
3 ). The membrane
(3000
× 3000is×supported
12 µm3 ) coated
an aluminum
layer
(2500
×Figure
2500
µman
3), ×
membrane
by thickness)
twowith
torsional
springs (2100
× 100
×in12
μm
in 0.8
which
aluminum
(30
μm width
and 0.8 μm
is deposited,
as shown
21.
The sensor
exploits wire
the
3 ), in which an aluminum wire (30 µm
isLorentz
supported
two
torsional
springs
(2100
× motion
100 ×as12
µm
(30
μm width
0.8
μm
thickness)
is deposited,
shown
in Figure
21.measured
The sensor
exploits
the
forcebyinand
order
to
generate
a rotational
of
the mirror
that is
with
the laser
width
andforce
0.8system.
µm
thickness)
is deposited,
as shown
inofFigure
21.
exploits
the
Lorentz
Lorentz
in order
generate
a rotational
motion
the mirror
thatsensor
is measured
with
the
laser
positioning
Totoincrease
the
sensitivity
of the
sensor,
the The
mirror
oscillates
at
resonance
force
in order
to generate
rotational
of theofmirror
thatapplied
is measured
the laser
positioning
system.
To aincrease
themotion
sensitivity
the sensor,
the magnetic
mirrorwith
oscillates
at positioning
resonance
(torsional
vibration
mode)
at atmospheric
pressure.
Thus,
the
field
is related
to the
system.
To
increase
the
sensitivity
of
the
sensor,
the
mirror
oscillates
at
resonance
(torsional
(torsional vibration
at atmospheric
pressure.
magneticpressure,
field is related
to the
displacements
of themode)
mirror.
For a coil bias
currentThus,
of 50 the
mAapplied
at atmospheric
thevibration
sensor
mode)
at atmospheric
Thus,
applied
magnetic
field
is
related
to the
displacements
displacements
of the pressure.
mirror.
For
a −1
coil
current
of 50 mA
atmospheric
pressure,
sensor
registers
a sensitivity
of 62 mV·
μT
, the
a bias
resonant
frequency
of at
364
Hz, a quality
factor the
of 116,
aof
−1
−1/2
the
mirror.
For
a
coil
bias
current
of
50
mA
at
atmospheric
pressure,
the
sensor
registers
a
sensitivity
registers
a
sensitivity
of
62
mV·
μT
,
a
resonant
frequency
of
364
Hz,
a
quality
factor
of
116,
resolution of 0.4 nT with a bandwidth of 53 mHz and noise floor level of 1.78 nT·Hz . This sensora
−1 , a resonant frequency of 364 Hz, a quality factor of 116, a resolution−1/2
ofcan
62 detect
mV·µTaof
0.4 nT
with
resolution
0.4 nT with
bandwidth
of 53of
mHz
and noise
floor
levelNevertheless,
of 1.78 nT·Hz
This
sensor
magnetic
fielda between
a range
nanoTeslas
and
Teslas.
theof.variation
of
−
1/2
a the
bandwidth
53 mHz
and
noise
floor
level
ofof1.78
nTand
·Hzsprings
. This
sensor
detect the
a magnetic
field
sensor
due
to heating
ofathe
membrane
should
be can
studied.
can
detect behavior
aof
magnetic
field
between
range
nanoTeslas
and
Teslas.
Nevertheless,
variation
of
between
a range
of nanoTeslas
and Teslas.
Nevertheless,
variation
ofbe
thestudied.
sensor behavior due to
the sensor
behavior
due to heating
of the membrane
and the
springs
should
heating of the membrane and springs should be studied.
Sensors2016,
2016,16,
16,1359
1359
Sensors
Sensors 2016, 16, 1359
16 of
of 25
25
16
16 of 25
(a)
(a)
(b)
(b)
Figure 21. (a) Microscope image of a MEMS magnetic field sensor with optical readout; and (b)
Figure 21.
21.principle
(a)(a)Microscope
of[34].
aofMEMS
magnetic
sensor
with
optical
and2016,
(b)
operation
of the image
sensor
withfield
permission
from
[34]. readout;
Copyright©
Figure
Microscope
image
aReprinted
MEMS
magnetic
field sensor
with
optical readout;
operation
principle
of
the
sensor
[34].
Reprinted
with
permission
from
[34].
Copyright©
2016,
Elsevier
B.V.
and
(b) operation
principle of the sensor [34]. Reprinted with permission from [34]. Copyright©2016,
Elsevier
B.V.
Elsevier B.V.
3. Potential Applications
3. Potential Applications
3. Potential
Applications
Magnetic
field sensors based on MEMS resonators have potential applications such as
Magnetic field sensors based on MEMS resonators have potential applications such as
telecommunications,
military, based
industrial,
automotive,
biomedical
consumer
electronic products.
Magnetic field sensors
on MEMS
resonators
haveand
potential
applications
such as
telecommunications, military, industrial, automotive, biomedical and consumer electronic products.
This
is
due
to
the
important
advantages
of
MEMS
sensors,
which
include
small
size,
lightweight,
telecommunications, military, industrial, automotive, biomedical and consumer electronic products.
This is due to the important advantages of MEMS sensors, which include small size, lightweight,
low power
consumer,
wide advantages
dynamic range,
compact
signal
conditioning
and high
These
This
is due to
the important
of MEMS
sensors,
which
include small
size,sensitivity.
lightweight,
low
low power consumer, wide dynamic range, compact signal conditioning and high sensitivity. These
sensorsconsumer,
could detect
or range,
residual
stresses
of ferromagnetic
materials
using non-destructive
power
wide flaws
dynamic
compact
signal
conditioning and
high sensitivity.
These sensors
sensors could detect flaws or residual stresses of ferromagnetic materials using non-destructive
testingdetect
such flaws
as Eddy
current stresses
inspection
and the magnetic
memory
method
(MMM) [35–37].
could
or residual
of ferromagnetic
materials
using
non-destructive
testing Eddy
such
testing such as Eddy current inspection and the magnetic memory method (MMM) [35–37]. Eddy
currents
are generated
on the
surface
of the ferromagnetic
material
when
a variable
magnetic
as
Eddy current
inspection
and
the magnetic
memory method
(MMM)
[35–37].
Eddy
currentsfield
are
currents are generated on the surface of the ferromagnetic material when a variable magnetic field
interacts with
this
surface.
The flaws of material
the ferromagnetic
material
alter
theinteracts
Eddy with
currents,
generated
on
the
surface
of
the
ferromagnetic
when
a
variable
magnetic
field
this
interacts with this surface. The flaws of the ferromagnetic material alter the Eddy currents,
modifying
field in relation
to the
sizethe
of the flaws.
For instance,
an array
of magnetic
surface.
Thetheir
flawsmagnetic
of the ferromagnetic
material
alter
currents,
modifying
field
modifying
their
magnetic
field in relation
to the
size of Eddy
the flaws.
For instance,
antheir
arraymagnetic
of magnetic
field
sensors
could
detect
flaws
ofFor
an instance,
oil pipeline
(see
Figure
22) using
thesensors
Eddy currents
technique
in
relation
to
the
size
of
the
flaws.
an
array
of
magnetic
field
could
detect
flaws
field sensors could detect flaws of an oil pipeline (see Figure 22) using the Eddy currents technique
[36].
the other(see
hand,
MMM
detect
residual stress of ferromagnetic
materials
through
of
an On
oil
Figure
22)can
using
theflaws
Eddyor
[36]. On the other
hand,
MMM
[36].
Onpipeline
the other hand,
MMM
can
detect
flaws
orcurrents
residualtechnique
stress of ferromagnetic
materials
through
the detect
variations
ofortheir
residual
magnetic
field. Thus,
magnetic
fieldthe
sensors
couldofmeasure
these
can
flaws
residual
stress
of
ferromagnetic
materials
through
variations
their
residual
the variations of their residual magnetic field. Thus, magnetic field sensors could measure these
modifications
ofThus,
a magnetic
field
related
to the
size measure
of the flaws,
ormodifications
magnitude ofof
thea residual
stress.
magnetic
field.
magnetic
field
sensors
could
these
magnetic
field
modifications of a magnetic field related to the size of the flaws, or magnitude of the residual stress.
Lara-Castro
et
al.
[37]
developed
a
portable
signal
conditioning
system
of
a
magnetic
field
sensor
related
to the et
size
thedeveloped
flaws, or magnitude
the residual
stress.system
Lara-Castro
et al. [37]field
developed
Lara-Castro
al.of[37]
a portable of
signal
conditioning
of a magnetic
sensor
Figure
23),
which
could
detect
residual
magnetic
field
of
ferromagnetic
materials
using
the
a(see
portable
signal
conditioning
system
of
a
magnetic
field
sensor
(see
Figure
23),
which
could
detect
(see Figure 23), which could detect residual magnetic field of ferromagnetic materials using
the
MMM.
residual
magnetic
field
of
ferromagnetic
materials
using
the
MMM.
MMM.
Figure 22. Design of a flaws inspection system in oil pipeline using Eddy current technique [36].
Figure
pipeline using
using Eddy
Eddy current
current technique
technique[36].
[36].
Figure22.
22. Design
Design of
of aa flaws
flaws inspection
inspection system in oil pipeline
Reprinted with permission from [36]. Copyright©2011, InTech.
Reprinted
InTech.
Reprintedwith
withpermission
permission from
from [36].
[36]. Copyright©
Copyright© 2011, InTech.
Domínguez-Nicolas
employing
MEMS
Domí
nguez-Nicolas et
et al.
al. [38]
[38] developed
developed aa respiratory
respiratory
magnetogram
Domí
nguez-Nicolas
al.
[38]
developed
respiratory magnetogram
magnetogram employing
employing aaa MEMS
MEMS
magnetic
field
sensor
with
piezoresistive
sensing
and
silicon
resonator
Figure
24).
This
device
magnetic
field
sensor
with
piezoresistive
sensing
and
silicon
(see
Figure
24).
This
device
magnetic field sensor with piezoresistive
silicon resonator (see Figure 24). This device
measuredthe
themagnetic
magneticfield
fieldduring
duringthe
therespiratory
activity of
measured
These
researchers
registered
the
measured
the
magnetic
field
during
the
respiratory activity
of rats.
rats. These
These researchers
researchersregistered
registeredthe
the
magnetogramand
andelectromyogram
electromyogram of
of the thoracic cavity of aa rat
magnetogram
rat during
during its
its respiration,
respiration,as
asshown
showninin
Sensors 2016, 16, 1359
17 of 25
Sensors 2016,
2016, 16,
16, 1359
1359
Sensors
17 of
of 25
25
17
magnetogram and electromyogram of the thoracic cavity of a rat during its respiration, as shown in
Figure 25.
25. For
For this
this magnetogram,
magnetogram, Juarez-Aguirre
Juarez-Aguirre et
et al.
al. [39]
[39] designed
designed aa digital
digital signal
signal processing
processing
Figure
Figure 25.
For this
magnetogram, Juarez-Aguirre
et al. [39]
designed
a digital signal processing
through
through
virtual
instrumentation.
A
future
application
of
this
magnetogram
could
be
used for
for
through
virtual
instrumentation.
A
future
application
of
this
magnetogram
could
be
used
virtual instrumentation. A future application of this magnetogram could be used for monitoring the
monitoring
the
health
of
some
organs
of
the
thoracic
cavity.
For
instance,
healthy
organs
of
the
monitoring
the organs
health of
organs cavity.
of the thoracic
cavity.healthy
For instance,
organs of
the
health of some
of some
the thoracic
For instance,
organs healthy
of the thoracic
cavity
thoracic cavity
cavity (e.g.,
(e.g., heart)
heart) could
could generate
generate magnetic
magnetic fields
fields in
in aa determined
determined range;
range; unhealthy
unhealthy organs
organs
thoracic
(e.g., heart) could generate magnetic fields in a determined range; unhealthy organs however, could
however, could
could cause
cause abnormal
abnormal magnetic fields.
fields. More research
research related
related to
to magnetic
magnetic fields
fields emitted
emitted by
by
however,
cause abnormal
magnetic fields.magnetic
More researchMore
related to magnetic
fields
emitted by healthy
and
healthy and
and unhealthy
unhealthy organs of
of the thoracic
thoracic cavity
cavity is
is required.
required. In addition,
addition, Tapia
Tapia et
et al.
al. [40]
[40] built
built an
an
healthy
unhealthy
organs of theorgans
thoracic the
cavity is required.
In addition,InTapia
et al. [40] built
an electronic
electronic
neuron
(FitzHugh-Nagumo)
to
generate
controlled
spike-like
magnetic
fields,
which
were
electronic
neuron (FitzHugh-Nagumo)
generate controlled
spike-likefields,
magnetic
fields,
which
were
neuron (FitzHugh-Nagumo)
to generatetocontrolled
spike-like magnetic
which
were
measured
measured with
with aa MEMS
MEMS sensor.
sensor. In
In future
future applications,
applications, this
this sensor
sensor could
could be
be improved
improved to
to detect
detect
measured
with a MEMS sensor. In future applications, this sensor could be improved to detect spiking activity of
spiking activity of
of neurons or
or muscle
muscle cells.
cells.
spiking
neuronsactivity
or muscle neurons
cells.
Figure 23.
23. Printed
Printed circuit
circuit board
board (PCB)
(PCB)
for aa portable
portable
signal
conditioning
system
of
MEMS
sensor,
Figure
(PCB) for
portable signal
signal conditioning
conditioning system
system of
of aaa MEMS
MEMS sensor,
sensor,
which
could
be
used
for
monitoring
residual
magnetic
field
of
ferromagnetic
materials
[37].
couldbebe
used
monitoring
residual
magnetic
of ferromagnetic
[37].
which could
used
for for
monitoring
residual
magnetic
field offield
ferromagnetic
materials materials
[37]. Reprinted
Reprinted
with
permission
from
[37].
Copyright©
2016,
Springer
International
Publishing
AG.
Reprinted
with permission
from [37]. Copyright©
2016,International
Springer International
AG.
with
permission
from [37]. Copyright©2016,
Springer
PublishingPublishing
AG.
Figure 24.
SEMimage
imageof
MEMSmagnetic
magneticfield
fieldsensor
sensorwith
withpotential
potentialapplication
applicationto
obtain
SEM
image
ofofaaaMEMS
MEMS
magnetic
field
sensor
with
potential
application
totoobtain
obtain
Figure
24. SEM
aa
a
respiratory
magnetogram
[38].
Reprinted
with
permission
from
Copyright©2013,
Ivyspring
respiratory
magnetogram
[38].
Reprinted
with
permission
from
[38].
Copyright©
2013,
respiratory magnetogram [38]. Reprinted with permission from [38]. Copyright© 2013, Ivyspring
International Publisher.
Publisher.
International Publisher.
Sensors 2016, 16, 1359
Sensors
Sensors 2016,
2016, 16,
16, 1359
1359
18 of 25
18
18 of
of 25
25
(a)
(b)
Figure
25.
set
up
sensor
for
monitoring
the
Figure 25.
25. (a)
(a) Diagram
Diagram of
of an
an experimental
experimental set
set up
up of
of aaa MEMS
MEMS magnetic
magnetic field
field sensor
sensor for
for monitoring
monitoring the
the
Figure
(a)
Diagram
of
an
experimental
of
MEMS
magnetic
field
respiratory
and
cardiac
activity
of
a
rat;
(b)
Electromyogram
of
the
thoracic
muscles
and
respiratory
and
cardiac
activity
of
a
rat;
(b)
Electromyogram
of
the
thoracic
muscles
and
respiratory and cardiac activity of a rat; (b) Electromyogram of the thoracic muscles and magnetogram
magnetogram
of
thoracic
during
the
of
rat
magnetogram
of the
theduring
thoracic
cavity
during
the respiratory
respiratory
activity
of aawith
rat [38].
[38]. Reprinted
Reprinted
with
of
the thoracic cavity
thecavity
respiratory
activity
of a rat [38].activity
Reprinted
permission
fromwith
[38].
permission
from
[38].
Copyright©
2013,
Ivyspring
International
Publisher.
permission
from
[38].
Copyright©
2013,
Ivyspring
International
Publisher.
Copyright©2013, Ivyspring International Publisher.
Other future applications of MEMS sensors include the micro-, nano- and pico-satellites.
Other future applications of MEMS sensors include the micro-, nano- and pico-satellites.
Miniaturization of satellites allows for the reduction of their launch costs, which can be achieved
Miniaturization of satellites allows for the reduction of their launch costs, which can be achieved using
using sensors of small size, reliable, low energy consumption and high sensitivity. For instance,
sensors of small size, reliable, low energy consumption and high sensitivity. For instance, satellites must
satellites must measure small magnetic fields during their space missions. For this application, Lamy
measure small magnetic fields during their space missions. For this application, Lamy et al. [41] and
et al. [41] and Ranvier et al. [42] designed MEMS sensors composed of polysilicon-xylophone bars
Ranvier et al. [42] designed MEMS sensors composed of polysilicon-xylophone bars and a capacitive
and a capacitive sensing. In addition, space satellites need inertial measurement units (IMUs)
sensing. In addition, space satellites need inertial measurement units (IMUs) formed by magnetic field
formed by magnetic field sensors, accelerometers and gyroscopes. These IMUs could be fabricated
sensors, accelerometers and gyroscopes. These IMUs could be fabricated on a single chip to decrease the
on a single chip to decrease the power consumption and electronic noise. Other IMUs applications
power consumption and electronic noise. Other IMUs applications will include the navigation systems
will include the navigation systems of ships, trains, military and civil aviation and unmanned
of ships, trains, military and civil aviation and unmanned operated vehicles [43–45]. Laghi et al. [46]
operated vehicles [43–45]. Laghi et al. [46] fabricated a torsional MEMS sensor through surface
fabricated a torsional MEMS sensor through surface micromachining for monitoring in-plane magnetic
micromachining for monitoring in-plane magnetic field, as shown in Figure 26. This sensor operates
field, as shown in Figure 26. This sensor operates with the Lorentz force and capacitive sensing.
with the Lorentz force and capacitive sensing. This device has the following technical parameters:
This device has the following technical parameters: size of 282 × 1095 µm2 , vacuum packaging of
size of 282 × 1095 μm22, vacuum packaging of 0.35 mbar, resonant frequency of 19.95 kHz, quality
0.35 mbar, resonant frequency of 19.95 kHz, quality factor of 2500, a sensitivity of 0.85 V·mT−1 and
−1 and a detection limit of 120 nT·mA·Hz−1/2
−1/2.
factor of 2500, a sensitivity of 0.85 V·mT−1
a detection limit of 120 nT·mA·Hz−1/2 .
Figure
26.
IMUs
Figure 26.
26. (a)
(a)
SEM image
image of
of aa MEMS
MEMS magnetic
magnetic field
field sensor
sensor with
with capacitive
capacitive sensing
sensing for
for IMUs
IMUs
Figure
(a) SEM
applications;
(b)
Top
view;
(c)
the
of
sensor
[46].
applications;(b)
(b)Top
Top
view;
and
(c) cross-section
cross-section
of
the operating
operating
principle
of the
the
sensor
[46].
applications;
view;
andand
(c) cross-section
of theof
operating
principleprinciple
of the sensor
[46].
Reprinted
Reprinted
with
from
2015,
B.
Reprinted
with permission
permission
from [46].
[46]. Copyright©
Copyright©
2015,
Elsevier
B. V.
V.
with
permission
from [46]. Copyright©2015,
Elsevier
B.Elsevier
V.
Trafficdetection
detectionsystems
systems
could
measure
the speed
andofsize
of vehicles
considering
MEMS
Traffic
could
measure
the speed
and size
vehicles
considering
MEMS devices,
devices,
areinlocated
parallel alongside
the road
These
devices
have separation
a constant
which
arewhich
located
parallelinalongside
the road [36].
These[36].
devices
will
have awill
constant
separation distance and will detect the variation of Earth’s magnetic field generated by the motion of
the vehicles, as shown in Figure 27. These changes can be measured at different times (t11 and t22)
Sensors 2016, 16, 1359
19 of 25
distance
and
Sensors
2016,
16, will
1359 detect
the variation of Earth’s magnetic field generated by the motion of the vehicles,
19 of 25
as shown in Figure 27. These changes can be measured at different times (t1 and t2 ) using the MEMS
using
theThus,
MEMS
devices.
Thus,
vehicle
speed will
determined
theseparation
ratio of the
devices
devices.
vehicle
speed
will be
determined
usingbethe
ratio of theusing
devices
distance
to
separation
distancet1 to
difference
t1 and
t2. Thewith
vehicle
size will change
be related
with
the
the time difference
andthe
t2 . time
The vehicle
size will
be related
the magnitude
of the
Earth’s
magnitude
change of the Earth’s magnetic field.
magnetic field.
Figure 27.
view
of traffic
detection
systemsystem
formed formed
by MEMS
signal and
processing
27.Schematic
Schematic
view
of traffic
detection
bydevices
MEMSand
devices
signal
[36].
Reprinted
permission
from [36]. Copyright@2011,
Intech.
processing
[36].with
Reprinted
with permission
from [36]. Copyright@2011,
Intech.
4.
4. Comparisons
Comparisonsand
andChallenges
Challenges
MEMS
force-based magnetic
sensors offer
offer several
several advantages
advantages
MEMS resonators
resonators used
used in
in Lorentz
Lorentz force-based
magnetic field
field sensors
with
respect to
to conventional
conventional sensors,
sensors, allowing
allowing for
for their
their use
use in
in future
future applications.
applications. The
with respect
The Lorentz
Lorentz
force-based
sensors
provide
a
wide
measurement
range
by
changing
the
magnitude
of
the
excitation
force-based sensors provide a wide measurement range by changing the magnitude of the excitation
current.
current. In
In addition,
addition, vacuum
vacuum packaging
packaging reduces
reduces the
the air
air damping,
damping, increasing
increasing the
the quality
quality factor
factor and
and
sensitivity
ofthe
theMEMS
MEMS
resonators.
These
sensors
low energy
consumption
and
have a
sensitivity of
resonators.
These
sensors
needneed
a lowaenergy
consumption
and have
a compact
compact
can bethrough
fabricated
throughmicromachining
a standard micromachining
process.sensors
Also,
structure,structure,
which canwhich
be fabricated
a standard
process. Also, MEMS
MEMS
use different
sensing
techniques (e.g.,
piezoresistive,
optical,
or magnetic
capacitive)
to
can use sensors
differentcan
sensing
techniques
(e.g., piezoresistive,
optical,
or capacitive)
to detect
field.
detect
magnetic
field.
Each
technique
presents
specific
benefits
that
are
employed
for
the
designers
Each technique presents specific benefits that are employed for the designers to develop the best sensor
to
the
best sensorFor
forexample,
a specificpiezoresistive
application. For
example,
piezoresistive
sensing
is adequate
fordevelop
a specific
application.
sensing
is adequate
for the bulk
micromachining
for
the bulk
micromachining
process systems.
and simple
signal
systems.
With
thesesignal
systems,
an
process
and simple
signal processing
With
theseprocessing
systems, an
electrical
output
related
electrical
output
signal
related
with
the
magnetic
field
is
obtained.
The
piezoresistive
sensing
with the magnetic field is obtained. The piezoresistive sensing registers a voltage offset and requires
registers
a voltage
offset and
requires
compensation
circuits. isOn
the other
hand,
temperature
compensation
circuits.
On temperature
the other hand,
capacitive sensing
mostly
used in
the
capacitive
sensing is mostly
used and
in the
superficial
micromachining
it converts
the
superficial micromachining
process
it converts
the applied
magnetic process
field intoand
an electrical
output
applied
magnetic
field
electricaldependence
output signal.
This technique
has oflittle
temperature
signal. This
technique
hasinto
little an
temperature
and allows
the fabrication
electronic
circuits
dependence
and allows
the fabrication
of electronic
circuits
on the same
chip
of the
magnetic
field
on the same chip
of the magnetic
field sensor.
It permits
the reduction
of the
device
size
and parasitic
sensor.
It
permits
the
reduction
of
the
device
size
and
parasitic
capacitances.
Generally,
the
sensors
capacitances. Generally, the sensors with capacitive sensing have high air damping at atmospheric
with
capacitive
sensing
air damping
at atmospheric
pressure;
therefore
theyoptical
need vacuum
pressure;
therefore
theyhave
needhigh
vacuum
packaging
to increase their
sensitivity.
Finally,
sensing
packaging
to increase
their sensitivity.
Finally,
optical
sensing has
electromagnetic
has immunity
to electromagnetic
interference
(EMI)
and demands
lessimmunity
electronic to
circuitry
than both
interference
(EMI)
and demands
less electronic
circuitry
bothcan
capacitive
piezoresistive
capacitive and
piezoresistive
sensing.
Sensors with
opticalthan
sensing
operate and
in hostile
or harsh
sensing.
Sensors
with
optical
sensing
can
operate
in
hostile
or
harsh
environments
without
environments without providing energy for the sensor. The superficial and bulk micromachining
providing
energy
for the
The superficial
andNevertheless,
bulk micromachining
are suitable
for
processes are
suitable
forsensor.
this sensing
technique.
all these processes
sensing techniques
have
this
sensing
technique.
Nevertheless,
all
these
sensing
techniques
have
problems
with
the
heating
of
problems with the heating of the sensor structure due to the Joule effect, generating thermal stress and
the
sensor structure
due to the More
Joule studies
effect, generating
thermal stress
displacements
of the
displacements
of the resonators.
about the modifications
in and
the behavior
of the MEMS
resonators.
More
studies
about
the
modifications
in
the
behavior
of
the
MEMS
resonators
due
to the
resonators due to the Joule effect must be performed. In addition, the mechanical reliability of
the
Joule
effect
must
be
performed.
In
addition,
the
mechanical
reliability
of
the
resonators
must
be
resonators must be studied to ensure the best performance of the MEMS sensors.
studied to ensure the best performance of the MEMS sensors.
Table 1 depicts some characteristics of magnetic field sensors composed by resonators and
fabricated with micromachining process. Recently, MEMS magnetic field devices have been
developed with important advantages for future commercial markets. To guarantee a reliable
Sensors 2016, 16, 1359
20 of 25
Table 1 depicts some characteristics of magnetic field sensors composed by resonators and
fabricated
micromachining process. Recently, MEMS magnetic field devices have been developed
Sensors 2016,with
16, 1359
20 of 25
with important advantages for future commercial markets. To guarantee a reliable performance of
performance
theseresearches
devices, more
mustrespect
be made
with respect
to vacuum
packaging,
these
devices,ofmore
must researches
be made with
to vacuum
packaging,
dependence
on
dependence
on changes
humidity and
temperature,
as well
as a reduction
ofnoise.
voltage
offset
and
changes
of humidity
and of
temperature,
as well
as a reduction
of voltage
offset and
With
respect
noise.
With respect
to the reduction
of electronic
noise,
Minotti aetmagnetic
al. [47] developed
a magnetic
to
the reduction
of electronic
noise, Minotti
et al. [47]
developed
field sensor
(see Figurefield
28)
sensor
(see Figure
28) with
a custom
integrated
readout
circuit containing
a capacitive-sensing
with
a custom
integrated
readout
circuit
containing
a capacitive-sensing
front-end,
a mixer and
a mixer
and ademodulation.
low-pass filterThis
forsensor
signalhas
demodulation.
This sensor
has accelerations
tuning fork
afront-end,
low-pass filter
for signal
tuning fork geometry
to reject
geometry
to
reject
accelerations
and
vibrations
and
multiple
loops
to
increase
its
sensitivity.
It
and vibrations and multiple loops to increase its sensitivity. It operates in off-resonance mode to
operates inboth
off-resonance
to overcome
both
between
bandwidth
and resolution
and
overcome
trade-offs mode
between
bandwidth
andtrade-offs
resolution
and long-term
stability.
The sensor
is
long-term
stability.
The
sensor
is
fabricated
using
the
thick
epitaxial
layer
for
microactuators
and
fabricated using the thick epitaxial layer for microactuators and accelerometers (ThELMA) process
accelerometers
(ThELMA)
process
from CMOS
STMicroelectronics
[28]. A 0.35-μm CMOS
process
from
from
STMicroelectronics
[28].
A 0.35-µm
process from AustriaMicroSystem
(AMS)
is used
to
AustriaMicroSystem
(AMS)
is In
used
to fabricate
the integrated
circuit.
In29)
addition,
theconsumption
overall system
fabricate
the integrated
circuit.
addition,
the overall
system (see
Figure
has a low
of
−1·mA−1,
−
1
−
1
(see
Figure
29)
has
a
low
consumption
of
power
close
to
775
μW,
a
sensitivity
of
0.75
zF·
nT
power close to 775 µW, a sensitivity of 0.75 zF·nT ·mA , and packaging pressures of about 0.75 mbar.
and packaging
pressures
of aboutranges
0.75 mbar.
it can
reach large
ranges which
up to ±2.4
mT,
Thus,
it can reach
large full-scale
up toThus,
±2.4 mT,
adjusting
the full-scale
driving current,
exceeds
adjusting
the
driving
current,
which
exceeds
the
full-scale
of
conventional
devices
such
as
the
Hall
the full-scale of conventional devices such as the Hall effect and anisotropic magneto-resistance
effect and
anisotropic magneto-resistance (AMR) [48].
(AMR)
[48].
Figure 28.
28. SEM
SEM image
image of
of diamond-shaped
diamond-shaped tuning fork, including 10 metal
metal coils
coils deposited
deposited over
over the
the
Figure
springs and parallel plate (PP) cells. These cells are employed for capacitive readout and tuning
[47].
tuning [47].
Reprinted with
with permission
permission from
from [47].
[47]. Copyright@2015,
Copyright@2015, IEEE.
Reprinted
Reliability studies
thethe
devices
behavior
under
different
environments
and
Reliability
studies are
arerequired
requiredtotoknow
know
devices
behavior
under
different
environments
operation
conditions.
In
addition,
studies
of
the
main
damping
sources
of
resonators
must
be
and operation conditions. In addition, studies of the main damping sources of resonators must be
considered ininthe
the
design
phase
of devices
[49,50].
Designers
use
thesetostudies
to obtain
considered
design
phase
of devices
[49,50].
Designers
can usecan
these
studies
obtain resonators
resonators
with
minimum
damping,
which
will
improve
their
quality
factor
and
resolution.
Vacuum
with minimum damping, which will improve their quality factor and resolution. Vacuum packaging
packaging
can
decrease
the
air
damping
at
resonators,
increasing
their
performance.
can decrease the air damping at resonators, increasing their performance. Future applicationsFuture
need
applications need
multifunctional
sensors
forphysical
monitoring
several (e.g.,
physical
parameters
(e.g.,
multifunctional
sensors
for monitoring
several
parameters
acceleration,
magnetic
acceleration,
magnetic
field,
angular
ratio,
humidity,
temperature
and
gases).
For
this,
MEMS
field, angular ratio, humidity, temperature and gases). For this, MEMS technology will allow
technology
will of
allow
the integration
of a
different
sensorsFuture
on a single
chip.
Future
sources as
the
integration
different
sensors on
single chip.
energy
sources
asenergy
microgenerators
microgenerators
incorporated
into
the
devices
could
provide
them
with
their
own
power,
incorporated into the devices could provide them with their own power, therefore eliminatingtherefore
batteries.
eliminating
batteries.ofAlso,
more studies
of magnetic
be made
to improve
Also,
more studies
magnetic
stochastic
resonancestochastic
could beresonance
made to could
improve
the detection
of
the
detection
of
magnetic
fields.
This
stochastic
resonance
applied
to
magnetic
field
sensors
could
magnetic fields. This stochastic resonance applied to magnetic field sensors could help to increase
help dynamic
to increase
their
dynamic
range
and
[51].
For this
reason,
sensors
should consider
their
range
and
sensitivity
[51].
Forsensitivity
this reason,
sensors
should
consider
stochastic-resonance
stochastic-resonance
coils
on
the
same
chip,
in
which
these
coils
could
be
fabricated
with
metallic
coils on the same chip, in which these coils could be fabricated with metallic coils around
the
active
coilsof
around
the active area of the sensors.
area
the sensors.
Sensors 2016, 16, 1359
21 of 25
Table 1. Main characteristics of recent MEMS magnetic field sensors based on Lorentz force.
Magnetic Field Sensor
Resonator Size (µm × µm)
Resonant Frequency (kHz)
Quality Factor
Herrera-May et al. [25]
Mehdizadeh et al. [26]
Herrera-May et al. [27]
Zhang et al. [29]
Langfelder et al. [28]
Li et al. [30]
Laghi et al. [46]
Minotti et al. [47]
Park et al. [34]
400 × 150
500 × 1400
472 × 300
600 × 800
89 × 868
1200 × 680
282 × 1095
1700 × 750
3000 × 3000
136.52
2550
100.7
49.3
28.3
21.9
19.95
20
0.36
842
16,900
419.6
100,000
327.9
540
2,500
460
116
Noise
57.5
nV·Hz−1/2
*
— **
37.1 nV·Hz−1/2 *
— **
557.2 µV·Hz−1/2 *
0.5 ppm·Hz−1/2
— **
30 zF·Hz−1/2
1.78 nT·Hz−1/2
* Theoretical data; ** Data do not available in the literature.
Detection Limit
143
nT·Hz−1/2
*
—**
161 nT·Hz−1/2 *
— **
520 nT·mA·Hz−1/2
— **
120 nT·mA·Hz−1/2
40 nT·mA·Hz−1/2
0.4 nT with BW = 53 mHz
Sensitivity
403 mV·T−1
262 mV·T−1
230 mV·T−1
215.74 ppm·T−1
150 µV·µT−1
6687 ppm·mA−1 ·T−1
0.85 V·mT−1
0.75 zF·nT−1 ·mA−1
62 mV·µT−1
Sensors 2016, 16, 1359
Sensors 2016, 16, 1359
22 of 25
22 of 25
Figure 29.
29. Photography
Figure
Photography showing
showingthe
thestaked
stakedMEMS
MEMSand
andASIC
ASICdies,
dies,which
whichare
arewire-bonded
wire-bondedonona
socket
carrier
located
on
the
biasing
PCB
board
[47].
Reprinted
with
permission
a socket carrier located on the biasing PCB board [47]. Reprinted with permission from
from [47].
[47].
Copyright@2015,
IEEE.
Copyright@2015, IEEE.
5. Conclusions
5. Conclusions
Magnetic field sensors formed by MEMS resonators have important advantages in respect to
Magnetic field sensors formed by MEMS resonators have important advantages in respect
conventional devices, allowing for their implementation in future applications. Most of these sensors
to conventional devices, allowing for their implementation in future applications. Most of these
use silicon resonators that exploit the Lorentz force and different sensing techniques such as
sensors use silicon resonators that exploit the Lorentz force and different sensing techniques such as
piezoresistive, optical, or capacitive. The piezoresistive sensing is a simple technique with an easy
piezoresistive, optical, or capacitive. The piezoresistive sensing is a simple technique with an easy
fabrication process; although it can have voltage offset and temperature dependence. Capacitive
fabrication process; although it can have voltage offset and temperature dependence. Capacitive
sensing has little temperature dependence but suffers from parasitic capacitances, which can be
sensing has little temperature dependence but suffers from parasitic capacitances, which can be
decreased with monolithic fabrication. Optical readout offers immunity to electromagnetic
decreased with monolithic fabrication. Optical readout offers immunity to electromagnetic interference
interference (EMI) and decreases the electronic components. The main fabrication processes include
(EMI) and decreases the electronic components. The main fabrication processes include surface and
surface and bulk micromachining, considering materials such as silicon, polysilicon, silicon dioxide,
bulk micromachining, considering materials such as silicon, polysilicon, silicon dioxide, aluminum
aluminum and gold. However, MEMS devices need more reliability research in order to predict their
and gold. However, MEMS devices need more reliability research in order to predict their performance
performance under different environments and operation conditions. Future works must consider
under different environments and operation conditions. Future works must consider the reduction
the reduction of damping and electronic noise, as well as the integration of different sensors on a
of damping and electronic noise, as well as the integration of different sensors on a single chip for
single chip for monitoring several physical parameters.
monitoring several physical parameters.
Acknowledgments: This
This work
work was
was partially
partially supported
supported by
by Sandia
Sandia National
National Laboratory’s
Laboratory’s University
University Alliance
Alliance
Acknowledgments:
PRODEP “Estudio
“Estudio de
de Dispositivos
Dispositivos
Program, FORDECYT-CONACYT through Grant 115976, and projects PRODEP
Electrónicos y Electromecánicos
Electromecánicos con Potencial
Potencial Aplicación en Fisiología
Fisiología yy Optoelectrónica”
Optoelectrónica” and
and “Sistema
“Sistema
Electrónico
Residual
de de
Estructuras
Ferromagnéticas”.
TheThe
authors
would
like
Electrónico de
deMedición
Mediciónde
deCampo
CampoMagnético
Magnético
Residual
Estructuras
Ferromagnéticas”.
authors
would
to thank Eduard Figueras from IMB-CNM (CSIC) for his collaboration into the fabrication of MEMS magnetometers
like to thank Eduard Figueras from IMB-CNM (CSIC) for his collaboration into the fabrication of MEMS
and Fernando Bravo-Barrera from LAPEM for his assistance with the SEM images.
magnetometers and Fernando Bravo-Barrera from LAPEM for his assistance with the SEM images.
Author Contributions: Agustín Leobardo Herrera-May, Juan Carlos Soler-Balcazar and Héctor Vázquez-Leal wrote
Author
Contributions:
Agustí
n Leobardo
Herrera-May,
Juan Carlos Soler-Balcazar
and Héctor
Vázquez-Leal
the
sections
of introduction,
design
and fabrication.
Jaime Martínez-Castillo,
Marco Osvaldo
Vigueras-Zuñiga
and
Luz
Antonio
Aguilera-Cortés
wrote the sections
potential
applications,
and challenges.
wrote
the sections
of introduction,
design of
and
fabrication.
Jaime comparisons
Martínez-Castillo,
Marco Osvaldo
Vigueras-Zuñiga
andThe
Luzauthors
Antonio
Aguilera-Cortés
wrote
the sections of potential applications, comparisons
Conflicts
of Interest:
declare
no conflict of
interest.
and challenges.
References
Conflicts of Interest: The authors declare no conflict of interest.
1.
Senturia, S.D. Microsystem Design; Kluwer Academic Publishers: New York, NY, USA, 2002.
References
2.
Allen, J.M. Mechanical System Design; Taylor & Francis: Boca Raton, FL, USA, 2005.
3.
Acevedo-Mijangos,
J.; Soler-Balcázar,
C.; Vazquez-Leal,
H.; Martínez-Castillo,
J.; Herrera-May,
1.
Senturia, S.D. Microsystem
Design; Kluwer
Academic Publishers:
New York, NY,
USA, 2002. A.L. Design
and
modeling
of a novelSystem
microsensor
detect&
magnetic
two orthogonal
directions. Microsyst. Technol.
2.
Allen,
J.M. Mechanical
Design;toTaylor
Francis:fields
Boca in
Raton,
FL, USA, 2005.
2013,
19, 1897–1912. [CrossRef]
3.
Acevedo-Mijangos,
J.; Soler-Balcázar, C.; Vazquez-Leal, H.; Martínez-Castillo, J.; Herrera-May, A.L.
Design and modeling of a novel microsensor to detect magnetic fields in two orthogonal directions.
Microsyst. Technol. 2013, 19, 1897–1912.
Sensors 2016, 16, 1359
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
23 of 25
Dominguez-Nicolas, S.M.; Juárez-Aguirre, R.; García-Ramírez, P.J.; Herrera-May, A.L. Signal Conditioning
System with a 4–20 mA Output for a Resonant Magnetic Field Sensor Based on MEMS Technology.
IEEE Sens. J. 2012, 12, 935–942. [CrossRef]
Wu, G.Q.; Xu, D.H.; Xiong, B.; Che, L.F.; Wang, Y.L. Design, fabrication and characterization of a resonant
magnetic field sensor based on mechanically coupled dual-microresonator. Sens. Actuators A 2016, 248, 1–5.
[CrossRef]
Bagherinia, M.; Bruggi, M.; Corigliano, A.; Mariani, S.; Horsley, D.A.; Li, M.; Lasalandra, E. An efficient earth
magnetic field MEMS sensor: Modeling, experimental results, and optimization. J. Microelectromech. Syst.
2015, 24, 887–895. [CrossRef]
Sonmezoglu, S.; Li, M.; Horsley, D.A. Force-rebalanced Lorentz force magnetometer based on
a micromachined oscillator. Appl. Phys. Lett. 2015, 106. [CrossRef]
Li, M.; Sonmezoglu, S.; Horsley, D.A. Extended bandwidth Lorentz force magnetometer based on quadrature
frequency modulation. J. Micromech. Microeng. 2015, 24, 333–342. [CrossRef]
Herrera-May, A.L.; Aguilera-Cortés, L.A.; García-Ramírez, P.J.; Manjarrez, E. Resonant magnetic field sensors
based on MEMS technology. Sensors 2009, 9, 7785–7813. [CrossRef] [PubMed]
Terauchi, N.; Noguchi, S.; Igarashi, H. Numerical simulation of DC SQUID taking into account quantum
characteristic of Josephson junction. IEEE Trans. Magn. 2015, 51. [CrossRef]
Mohamadabadi, K.; Jeandet, A.; Hillion, M.; Coillot, C. Autocalibration method for anisotropic
magnetoresistive sensors using offset coils. IEEE Sens. J. 2013, 13, 772–776. [CrossRef]
Popovic, R.S.; Drljaca, P.M.; Schott, C. Bridging the Gap between AMR, GMR, and Hall Magnetic Sensors.
In Proceedings of the 23rd International Conference on Microelectronics, Nis, Yugoslavia, 12–15 May 2002;
pp. 55–58.
Lei, C.; Lei, J.; Yang, Z.; Wang, T.; Zhou, Y. A low power micro fluxgate sensor with improved magnetic core.
Microsyst. Technol. 2013, 19, 591–598. [CrossRef]
Zha, X.F. Manufacturing advisory service system for concurrent and collaborative design of MEMS devices.
In MEMS/NEMS Handbook; Leondes, C.T., Ed.; Springer: New York, NY, USA, 2006; Volume 1, pp. 1–34.
MEMS CAP Inc. Available online: http://www.memscap.com/ (accessed on 22 March 2016).
Coventor Inc. Available online: http://www.coventor.com/ (accessed on 22 March 2016).
IntelliSense Inc. Available online: http://intellisense.com/ (accessed on 22 March 2016).
Sandia National Laboratories. Available online: http://www.sandia.gov/mstc/_assets/documents/design_
docu-ments/SUMMiT_V_Dmanual.pdf (accessed on 16 October 2015).
Acevedo-Mijangos, J.; Vázquez-Leal, H.; Martínez-Castillo, J.; Herrera-May, A.L. Theoretical design
and simulation of a novel 2D magnetic field sensor with linear response and low power consumption.
Micro Nanosyst. 2013, 5, 70–79. [CrossRef]
Allen, J.J. Micro Electro Mechanical System Design; Taylor and Francis Group: Boca Raton, FL, USA, 2005;
pp. 68–84.
Herrera-May, A.L.; García-Ramírez, P.J.; Aguilera-Cortés, L.A.; Figueras, E.; Martínez-Castillo, J.;
Manjarrez, E.; Sauceda, A.; García-González, L.; Juárez-Aguirre, R. Mechanical design and characterization
of a resonant magnetic field microsensor with linear response and high resolution. Sens. Actuators A 2011,
165, 399–409. [CrossRef]
Beeby, S.; Ensell, G.; Kraft, M.; White, N. MEMS Mechanical Sensors; Artech House: Norwood, MA, USA, 2004.
Hao, Z.; Erbil, A.; Ayazi, F. An analytical model for support loss in micromachined beam resonators with
in-plane flexural vibrations. Sensors 2003, 109, 156–164. [CrossRef]
Turvir, K.; Ru, C.Q.; Mioduchowski, A. Thermoelastic dissipation of hollow micromechanical resonators.
Phys. E Low Dimens. Syst. Nanostruct. 2010, 42, 2341–2352.
Herrera-May, A.L.; García-Ramírez, P.J.; Aguilera-Cortés, P.J.; Martínez-Castillo, J.; Sauceda-Carvajal, A.;
García-González, L.; Figueras-Costa, E. A resonant magnetic field microsensor with high quality factor at
atmospheric pressure. J. Micromech. Microeng. 2009, 19. [CrossRef]
Mehdizadeh, E.; Kumar, V.; Pourkamali, S. Sensitivity enhancement of Lorentz force MEMS resonant
magnetometers via internal thermal-piezoresistive amplification. IEEE Eectron Device Lett. 2014, 35, 268–270.
[CrossRef]
Sensors 2016, 16, 1359
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
24 of 25
Herrera-May, A.L.; Lara-Castro, M.; López-Huerta, F.; Gkotsis, P.; Raskin, J.-P.; Figueras, E. A MEMS-based
magnetic field sensor with simple resonant structure and linear electrical response. Microelectron. Eng. 2015,
142, 12–21. [CrossRef]
Langfelder, G.; Buffa, C.; Frangi, A.; Tocchio, A.; Lasandra, E.; Longoni, A. Z-axis magnetometers for MEMS
inertial measurement units using an industrial process. IEEE Trans. Ind. Electron. 2013, 60, 3983–3990.
[CrossRef]
Zhang, W.; Lee, J.E.-Y. Frequency-based magnetic field sensing Lorentz force axial strain modulation in
a double-ended tuning fork. Sens. Actuators A 2014, 211, 145–152. [CrossRef]
Li, M.; Nitzan, S.; Horsley, D.A. Frequency-modulated Lorentz force magnetometer with enhanced sensitivity
via mechanical amplification. IEEE Electron Device Lett. 2015, 36, 62–64.
Aditi; Gopal, R. Fabrication of MEMS xylophone magnetometer by anodic bonding technique using SOI
wafer. Microsyst. Technol. 2016. [CrossRef]
Vasquez, D.J.; Judy, J.W. Optically-interrogated zero-power MEMS magnetometer. J. Microelectromech. Syst.
2007, 16, 336–343. [CrossRef]
Markus, K.W.; Koester, D.A.; Cowen, A.; Mahadevan, R.; Dhuler, V.R.; Roberson, D.; Smith, L. MEMS
Infrastructure: The Multiuser MEMS process (MUMPs). In Proceedings of the SPIE Micromachining and
Microfabrication Process Technology, Austin, TX, USA, 23–24 October 1995; Volume 2639, pp. 54–63.
Park, B.; Li, M.; Lyyanage, S.; Shafai, C. Lorentz force based resonant MEMS magnetic-field sensor with
optical readout. Sens. Actuators A 2016, 241, 12–18. [CrossRef]
Dubov, A.; Dubov, A.; Kolokolnikov, S. Application of the metal magnetic memory method for detection of
defects at the initial stage of their development for prevention of failures of power engineering welded steel
structures and steam turbine parts. Weld. Word 2014, 58, 225–236. [CrossRef]
Herrera-May, A.L.; Aguilera-Cortés, L.A.; García-Ramírez, P.J.; Mota-Carrillo, N.B.; Padrón-Hernández, W.Y.;
Figueras, E. Development of Resonant Magnetic Field Microsensors: Challenges and Future Applications.
In Microsensors; InTech: Rijeka, Croatia, 2011; pp. 65–84.
Lara-Castro, M.; Herrera-May, A.L.; Juárez-Aguirre, R.; López-Huerta, F.; Ceron-Alvarez, C.A.;
Cortés-Mestizo, I.E.; Morales-González, E.A.; Vazquez-Leal, H.; Dominguez-Nicolas, S.M. Portable signal
conditioning system of a MEMS magnetic field sensor for industrial applications. Microsyst. Technol. 2016.
[CrossRef]
Domínguez-Nicolás, S.M.; Juárez-Aguirre, R.; Herrera-May, A.L.; García-Ramírez, P.J.; Figueras, E.;
Gutierrez, E.; Tapia, J.A.; Trejo, A.; Manjarrez, E. Respiratory magnetogram detected with a MEMS device.
Int. J. Med. Sci. 2013, 10, 1445–1450. [CrossRef] [PubMed]
Juárez-Aguirre, R.; Domínguez-Nicolás, S.M.; Manjarrez, E.; Tapia, J.A.; Figueras, E.; Vázquez-Leal, H.;
Aguilera-Cortés, L.A.; Herrera-May, A.L. Digital signal processing by virtual instrumentation of a MEMS
magnetic field sensor for biomedical applications. Sensors 2013, 13, 15068–15084. [CrossRef] [PubMed]
Tapia, J.A.; Herrera-May, A.L.; García-Ramírez, P.; Martínez-Castillo, J. Sensing magnetic flux density of
artificial neurons with a MEMS device. Biomed. Microdevices 2011, 13, 303–313. [CrossRef] [PubMed]
Lamy, H.; Rochus, V.; Niyonzima, I.; Rochus, P. A xylophone bar magnetometer for micro/pico satellites.
Acta Astronaut. 2010, 67, 793–809. [CrossRef]
Ranvier, S.; Rochus, V.; Druart, S.; Lamy, H.; Rochus, P.; Francis, L.A. Detection methods for MEMS-Based
xylophone bar magnetometer for pico satellites. J Mech. Eng. Autom. 2011, 1, 342–350.
Brigante, C.M.N.; Abbate, N.; Basile, A.; Faulisi, A.C.; Sessa, S. Towards miniaturization of a MEMS-based
wearable motion capture systems. IEEE Trans. Ind. Electron. 2011, 58, 3234–3241. [CrossRef]
Won, S.P.; Golnaraghi, F.; Melek, W.W. A fastening tool tracking system using an IMU and a position sensor
with Kalman filters and a fuzzy expert system. IEEE Trans. Ind. Electron. 2009, 56, 1782–1792. [CrossRef]
Dean, R.N.; Luque, A. Applications of microelectromechanical systems in industrial processes and services.
IEEE Trans. Ind. Electron. 2009, 56, 913–925. [CrossRef]
Laghi, G.; Dellea, S.; Longoni, A.; Minotti, P.; Tocchio, A.; Zerbini, S.; Lagfelder, G. Torsional MEMS
magnetometer operated off-resonance for in-plane magnetic field detection. Sens. Actuators A 2015, 229,
218–226. [CrossRef]
√
Minotti, P.; Brenna, S.; Laghi, G.; Bonfanti, A.G.; Langfelder, G.; Lacaita, A.L. A sub-400-nT/ Hz, 775-µm,
multi-loop MEMS magnetometer with integrated readout electronics. J. Microelectromech. Syst. 2015, 24,
1938–1950. [CrossRef]
Sensors 2016, 16, 1359
48.
49.
50.
51.
25 of 25
Langfelder, G.; Tocchio, A. Operation of Lorentz-force MEMS magnetometers with a frequency offset
between driving current and mechanical resonance. IEEE Trans. Magn. 2014, 50. [CrossRef]
Herrera-May, A.L.; Aguilera-Cortés, L.A.; García-González, L.; Figueras-Costa, E. Mechanical behavior
of a novel resonant microstructure for magnetic applications considering the squeeze-film damping.
Microsyst. Technol. 2009, 15, 259–268. [CrossRef]
Gkotsis, P.; Lara-Castro, M.; López-Huerta, F.; Herrera-May, A.L.; Raskin, J.-P. Mechanical characterization
and modelling of Lorentz force based MEMS magnetic field sensors. Solid State Electron. 2015, 112, 68–77.
[CrossRef]
Herrera-May, A.L.; Tapia, J.A.; Domínguez-Nicolás, S.M.; Juárez-Aguirre, R.; Gutierrez-D, E.A.; Flores, A.;
Figueras, E.; Manjarrez, E. Improved detection of magnetic signals by a MEMS sensor using stochastic
resonance. PLoS ONE 2014, 9, e109534.
© 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC-BY) license (http://creativecommons.org/licenses/by/4.0/).