Microsyst Technol (2014) 20:1041–1050
DOI 10.1007/s00542-014-2143-6
Review Paper
Numerical characterization and experimental verification
of an in‑plane MEMS‑actuator with thin‑film aluminum heater
Peter Meszmer · Karla Hiller · Steffen Hartmann · Alexey Shaporin · Daniel May ·
Raul David Rodriguez · Jörg Arnold · Gianina Schondelmaier · Jan Mehner ·
Dietrich R. T. Zahn · Bernhard Wunderle
Received: 24 December 2013 / Accepted: 7 March 2014 / Published online: 12 April 2014
© Springer-Verlag Berlin Heidelberg 2014
Abstract In this paper, a novel concept of a thermomechanical MEMS actuator using aluminum thin-film
heaters on a thermal oxide for electrical insulation is presented. The actuator is part of an universal tensile testing
platform for thermo-mechanical material characterization of one dimensional materials on a micro- and nanoscopic scale under different environmental conditions, as
varying temperatures, pressure, moisture or even vacuum
and is realised in BDRIE technology. It is shown, that the
actuator concept fulfills the requirements for the use in a
tensile loading stage along with heterogeneously integrated
nanofunctional elements, following a specimen centered
approach in line with bottom-up self-assembly processes.
Simulation and experiment agree very well in the thermal
P. Meszmer (*) · S. Hartmann · D. May · J. Arnold · B. Wunderle
Faculty for Electrical Engineering and Information Technologies,
Chair Materials and Reliability of Microsystems,
Technische Universität Chemnitz, 09107 Chemnitz, Germany
e-mail: peter.meszmer@etit.tu‑chemnitz.de
K. Hiller
Center for Microtechnologies ZfM,
Technische Universität Chemnitz, Chemnitz, Germany
A. Shaporin · J. Mehner
Faculty for Electrical Engineering and Information Technologies,
Chair of Microsystems and Precision Engineering,
Technische Universität Chemnitz, Chemnitz, Germany
R. D. Rodriguez · D. R. T. Zahn
Faculty of Natural Science, Institute of Physics,
Chair Semiconductor Physics,
Technische Universität Chemnitz,
Chemnitz, Germany
G. Schondelmaier
Zwickau, Germany
and mechanical domain and allow subsequent optimisation
of the actuator performance.
1 Introduction
The thermo-mechanical reliability of microelectronic
devices is based on an exact knowledge of the materialand failure-behavior and related parameters in the bulk and
at the interfaces under given relevant loading conditions,
derived from field conditions such as temperature, moisture
or vibration. The knowledge of this material and interface
behavior forms the basis of a physics-of-failure based lifetime model for predicting failure due to e.g. delamination,
which is one of the most important failure modes observed
in microelectronic interconnects. As these parameters are
extremely process dependent, the materials and interfaces
have to be characterized in their respective properties. On
the microscopic scale, over the years many methods have
been developed to do this by e.g. tensile or shear testing,
bending tests etc. (Wunderle and Michel 2009; Wunderle
et al. 2012; Durix et al. 2012), using standard or customized
equipment, with the purpose to correlate the experiments to
numerical methods for failure modeling by finite element
simulations or molecular dynamics simulations (e.g. Hölck
et al. 2012) for structure–property correlation.
For functional elements on the submicron or even
nanoscale, this procedure is, however, not feasible any more
for two reasons: first, these nano-functional elements, i.e.
the devices to be tested, cannot be clamped or fixed anymore
without sacrificing reproducibility, integrity or meaningfulness of the results. Second, very often those elements are
mounted by self-assembly bottom-up processes, as e.g. dielectrophoretically deposited CNTs (Yu et al. 2012, 2013). In
such a case, a top down assembly would not test a realistic
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interface. Therefore, new strategies have to be pursued and
new testing methods to be developed. This may entail, that
the loading mechanism or stage has to emerge around, and
more important, after the nano-functional element to be tested
is assembled. Such a philosophy is called specimen centered
approach. Here, this signifies, that the processes required to
create a loading stage have to be compatible with the process
flow of heterogeneous integration of the nano-functional elements. This is very challenging indeed. With this in mind,
MEMS-based actuators and sensors to form building blocks
of an universal micro-scale testing platform seem to be a
promising concept: wafer level processes allow inexpensive
and, as to be developed and shown, compatible processing
of the nano-functional elements under research. With such
MEMS-components at hand, it is envisaged to create a test
platform for nano-scale elements, which can be tensile tested
to obtain material bulk data or critical parameters during overload and can be used to characterize failure mechanisms of
nano-scale elements under various environmental conditions.
The range of specimens include, but is not limited to,
microfluidic tubes (Böttner et al. 2013), single wall carbon
nanotubes (SWCNTs) (Iijima 1991) and other one dimensional materials as silicon, boron nitride and aluminum based
nanowires, which are currently in the focus of research.
As we can show, even on the microscale, a tensile testing platform consists of three parts besides the specimen,
which have to be integrated into a single chip: an actuator, a sensor to measure the force and a sensor to measure the displacement, which we call building blocks.
Furthermore, we require for all building blocks the capability of electrical drive and electrical in situ readout,
respectively, to ensure the usability of the testing platform in a wide range of applications. A more general
description of a MEMS tensile testing platform, capable
of tests on a micro- and nano-scopic scale, has already
been presented by the authors in Schondelmaier et al.
(2013). The requirements for such a device are summarized in the following Sect. 2. This paper focuses on the
actuator, which is designed as thermal actuator. Following
our specimen centered approach, the designs of thermal
actuators presented in earlier papers as Riethmueller and
Benecke (1988), Jonsmann et al. (1999), Mankame and
Ananthasuresh (2001), Agrawal et al. (2011) are not fully
integrable. As of this, we developed the new approach of
a thermal actuator, fabricated in mono-crystalline silicon, processed by bonding and deep reactive ion etching
(BDRIE) and driven by an aluminum meander, located
on an insulating SiO2 layer. The electrical insulation thus
provided and the flexibility of a thermal actuator enables
us, in combination with the capabilities of the BDRIE
process, to reach the goal of a set of fully integrable
building blocks, which are electrically driven and provide
electrical in situ readout.
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Microsyst Technol (2014) 20:1041–1050
Fig. 1 Concept of a MEMS tensile testing platform
Table 1 Minimum requirements for the components of the MEMS
tensile testing platform
Displacement generated by actuator
Resolution of force sensor
>1 µm
<10 nN
Resolution of displacement sensor
<10 nm
2 Design specifications of a MEMS tensile testing
platform
The design of the components of the MEMS tensile testing platform, as shown in Fig. 1, is based on the requirements for the characterization of SWCNTs. These 800 up
to 2, 000 nm long structures, we are going to focus on, have
a modulus of elasticity of approximately 1 TPa (Wu et al.
2008). Considering a cross-section area of 100 Å2 , a force
of 100 nN can be estimated to achieve an elongation of 10 %.
As these considerations are very idealistic, we define the
following minimum requirements for the components of
the MEMS tensile testing platform (Table 1):
The designed MEMS tensile testing platform has to be
capable to examine samples under different environmental
condition as varying temperature, moisture, pressure and
even vacuum to account for later reliability testing under
real life conditions. Furthermore, all building blocks have
to be comparable with our already presented specimen centric approach, ensuring the full integration of specimen and
building blocks into a single chip.
3 Basic design and principles of operation of a thermal
actuator
Thermo-mechanical in-plane microactuators (TA) have
been described in publications as Riethmueller and
Benecke (1988), Jonsmann et al. (1999), Mankame and
Microsyst Technol (2014) 20:1041–1050
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Table 2 Parameters describing the thermal actuators used for the
characterization and experimental verification of numerical finite element based simulations
Number of arms
Length of arms
Hight of arms
Angle of arms
Offset between two arms
Thickness bulk silicon
Thickness SiO 2 insulator
Thickness aluminum
5 or 10
l = 230 µm
h = 10 µm
α = 5◦
d = 15 µm
zSi = 50 µm
zSiO2 = 300 nm
zAl = 100 nm
Fig. 2 Basic design of a thermal actuator with two ways of electrical
separation and insulation
Fig. 3 Parameters describing the geometry of the thermal actuator
Ananthasuresh (2001), Agrawal et al. (2011) and many
more: the given design variations usually share common
features and we are going to restrict ourselves to one of
these well knows designs as already presented in Jonsmann
et al. (1999) or Agrawal et al. (2011).
The chosen design can be described as a number of
V-shaped arms, anchored at the outer rim of the actuator. At
the tip of the V, all arms are connected by a shuttle, as shown
in Figs. 2 and 4. The arms are floating freely above a cavity as well as the shuttle, which allows these parts to move
laterally. The shuttle itself serves as connector to the remaining moving parts of the testing platform. The actuator is electrically driven using contact pads usually located near the
anchor points at the end of the V-shaped arms. Using these
contact pads, a voltage difference is applied resulting in a current flow across the arms and the shuttle. The high current
density causes joule heating. The resulting thermal expansion
expands the arms and results in a movement of the shuttle.
The key requirements, motivated by the needs for the
characterization of SWCNTs shown in Sect. 2, and the benefits of a thermal actuator can be summarized as follows:
• Small size compared to an electrostatic actuator,
• High robustness against environmental influences,
• Driven by low voltage in comparison to an electrostatic
actuator,
• No electrical stray fields which could interfere with
other components of the tensile testing platform.
Due to the fact, that the thermal actuator can not be considered alone, but is physically connected to the parts of the
tensile testing platform, it has to be electrically insulated.
This can in principle achieved by two different approaches:
• Vertical separation and insulation of the components:
this approach requires the growth of an insulator (black)
inside a vertical gap between at least two silicon based
components (gray) as shown in Fig. 2, top. This is technologically challenging.
• Horizontal separation and insulation: in such an
approach the heating of the bulk doped crystalline silicon (gray), which forms the bottom layer and the base
structure of the actuator, is done by an aluminum film
(light gray) forming a meandering structure on top of an
insulating silicon dioxide (black) layer (Fig. 2, bottom).
The authors have chosen the second path. Using bonding
and deep reactive ion etching (BDRIE, Hiller et al. 2005,
2013), as described in Sect. 4, layers of silicon separated by
silicon dioxide layers are created. In a subsequent processing step, the final structure is created by ion etching.
The thermal actuators used for the characterization and
experimental verification of numerical finite element based
simulations can be described by the parameters shown in
Table 2 and depicted in Fig. 3. These values are already
close to the simulated optimum.
In Fig. 4 the five armed version is shown. The aluminum pads for electric contacting, the meander, and the
aluminum covered part of the shuttle in the center, are easily recognizable by the bright white color. Following the
shuttle higher, the step from dark to lighter gray marks the
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Microsyst Technol (2014) 20:1041–1050
Fig. 4 Low resolution overview
of a TA provided by an optical
microscope
Figs. 5 and 8 (left), which is thermally homogenizing and
insulating and is acting as a joint. The effectivity of the
constrictions regarding temperature insulation is proven in
Sect. 6.2.
4 Bonding and deep reactive ion etching
Fig. 5 High resolution view on the connections between arms and
shuttle with aluminum meander provided by a TESCAN PROXIMA
SEM. Visible are the constrictions at the end of the arms
difference between the SiO 2 insulator and the bulk silicon.
The filigree fins left and right of the shuttle in the center of
the picture are created as heat dissipation areas. The 15 fins
have been a first layout option, which has to be optimized.
Following the shuttles arm higher, two simple springs, providing support to the whole structure while allowing lateral
movement, are visible. At the far end, the shuttle merges
into a pointer, leaving the picture to the right. This pointer
allows a verification of the activity of a TA by means of an
optical microscope.
The thermal actuator, discussed in this paper, is equipped
with a constriction at both ends of the arms, visible in
The BDRIE technology has been widely used before to
built electrostatic actuators and capacitive sensors (Hiller
et al. 2005, 2013). Thermal actuators can be easily fabricated both for direct actuation in silicon and for the horizontal separation approach described in Sect. 3.
The technology flow starts with a basic wafer, in which
a cavity is etched (Fig. 6, left). A second wafer is bonded
and thinned down to the desired thickness, in the here presented case 50 µm. Then the oxide layer is deposited and
patterned, followed by the metal layer structured to form
electrical contacts and the heating meanders (Fig. 6, right).
Finally, the actuator structure is etched into the silicon
using deep reactive ion etching (Fig. 7).
5 Characterization and optimization using finite
element simulations
There exists a number of software packages, that are suitable for the analysis of coupled field problems. One of
Fig. 6 Schematic process flow of the thermal actuator fabrication process: pre-etched cavity (left) and bonding and thinning of second wafer,
oxide and aluminum pattering
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Fig. 7 Schematic process flow of the thermal actuator fabrication
process: etching of deep trenches into the bulk silicon
Fig. 9 Results of finite element simulations (ANSYS) of the temperature distribution on the surface of a five armed TA using a
I = 105 mA (Is = 21 mA per arm) drive
Fig. 8 The elements of an ANSYS model. The area of the detail
shown left is marked with a rectangle on the overview right
these commercial software packages is ANSYS 14.x, providing code for the coupled field analysis involving electrical, thermal and mechanical fields. For the undertaken
simulations, the SOLID226 element was chosen, providing
20 nodes with up to five degrees of freedom per node. The
geometry is based on a cuboid.
Using the ANSYS package, the user is able to entirely
model the thermal actuator, define material properties and
apply boundary conditions. Additional input is given by the
strength of the electric current across the contact pads. Furthermore, at the contact pads zero displacement as mechanical and room temperature as thermal boundary condition is
applied, as well as the boundary conditions of heat dissipation by means of convection and radiation at the appropriate boundary elements.
The ANSYS model of the five armed TA is shown in
Fig. 8. The detail on the left side depicts the two uppermost arms and their connection to the shuttle (right).
Clearly visible are the already mentioned constrictions at
the end of the arms, acting as joints and being thermally
homogenizing.
The bulk silicon is shown in gray, the SiO2 insulator is
black and the aluminum is shown in light gray. The whole
TA can be described by the shown half-model, as the structure of the TA as well as the boundary conditions can be
considered as symmetric. Figure 9 plots the temperature
dissipation on the surface of a five armed TA, driven by
I = 105 mA (Is = 21 mA per arm).
Objective of the simulation is to analyze and optimize
the parameters related to the achievement of the maximum
lateral displacement △y. The free parameter space of a TA
is given by:
• Current I driving the thermo-mechanical in-plane
microactuator,
• Length l of the arms,
• Angle α of the arms,
• Thickness zSi of the bulk silicon,
• Thickness zSiO2 of the SiO2 insulator, and
• Thickness zAl of the aluminum meander.
Figure 10 presents the results obtained by finite element
simulations, based on various parameter sets. The percentage change of the target value—the lateral displacement
△y—is shown against the percentage change in the input
parameters starting from the values of a reference set. Its
easy to recognize that all parameters influence the target
value in a super-linear manner, except the thickness of the
insulating SiO2 layer, which has no quantifiable effect on
the lateral displacement.
Not all parameters can be tuned and optimized independently. The most prominent example is the thickness zSi of
the bulk silicon. Besides the fact that a thinner bulk silicon
layer would increase the lateral displacement, the bulk is
carrying the whole structure and is used for forming the
displacement sensor (Sun et al. 2002; Dienel 2009). This
sensor is a capacitive device and requires a well defined
thickness of this layer to reach the required accuracy given
in Sect. 2.
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Current I
Arm angle α
Arm length l
Thickness Al zAl
Thickness Si zSi
Thickness SiO2 zSiO2
Linear reference
150
Change in displacement y [%]
Fig. 10 Sensitivity analysis
of the lateral displacement
regarding the design parameters
of a TA based on finite element
simulations regarding a reference set
Microsyst Technol (2014) 20:1041–1050
100
50
0
−50
−100
−100
−50
0
50
100
150
Change of parameter [%]
Considering the integration of the TA into a tensile testing platform on a MEMS scale, the optimal design rules
are:
•
•
•
•
•
Maximize arm length l ,
Minimize angle α of the arms greater zero, and
Minimize thickness zAl of the aluminum layer regarding
Maximum electrical current I .
The size of the SiO2 insulator can be chosen regarding
the needs of electrical insulation, as it does not influence the lateral displacement.
6 Correlation and verification of numerical results
against experimental data
The mathematical model used for the numerical finite
element simulation is often based on ideal or simplified
assumptions and material parameters. Here however, all
material parameters and physical processes are known and
mathematically fully described. Nevertheless, the numerical methods should be correlated with experimental data to
verify material parameters and assumptions made by the
mathematical model.
In the following sections we are going to correlate and
verify numerically achieved results using experimental
methods.
6.1 Thermal characterization, infrared tomography
Infrared imaging, as shown in Fig. 11, provides a precise
and simple to achieve overview regarding the temperature
distribution of a TA. The measurements presented here are
made by an Infratec ImageIR 8300 camera, providing a lateral resolution of 5 µm using a cooled indium antimonide
(InSb) detector in combination with a proper infrared 3×
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Fig. 11 Infrared image of a five armed TA driven at I = 105 mA
(Is = 21 mA per arm)
Table 3 Experimentally determined emissivities of the relevant areas
of a TA
Silicon
0.93–0.97
Aluminum meander on top of SiO 2
0.89
microscopic lens. The temperature resolution of the device
is specified as <20 mK at room temperature and decreases
with increasing temperature.
Knowledge of the emissivity is important for a measurement of the absolute surface temperature. The emissivities of the relevant areas of a TA were experimentally
determined and used for correlation of the IR measurement
data. The following Table 3 summarizes the experimentally
determined values.
Figure 12 depicts the temperature at two points on the
lower and the upper end of the shuttle, respectively, using
different drive currents. The high accuracy was achieved
Microsyst Technol (2014) 20:1041–1050
Fig. 12 Temperature development measured on two points along the
shuttle of a five armed TA based on a variation of drive currents. Data
provided by infrared imaging and simulation
by tuning the thickness of the aluminum layer to 80 nm ,
which was later verified by white light interferometry as
shown in Sect. 6.3.
The thermal measurements were performed using an
actuator, those arms were not entirely etched free, possibly
leaving a thermal bridge below the arms. The simulations
did not take the existence of such a bridge into account. But
the high accordance of simulated data and experimentally
obtained results, depicted in Fig. 11, indicate, that the influence of the thermal bridge is negligible.
6.2 Local thermal characterization, Raman spectroscopy
Raman spectroscopy enables us to perform very precise
temperature measurements on a single point (Rodriguez
et al. 2012). All presented Raman measurements were performed in the backscattering geometry using the 632.8 nm
line of a helium–neon laser. The Raman spectrometer is a
LabRam HR800 from Horiba Scientific. A 100 x objective
was used to illuminate the sample and for the collection of
the Raman signal, yielding a diffraction limited resolution
of approximately 430 nm. A liquid nitrogen-cooled backilluminated charge-coupled device (CCD) was used for
detection of the Raman signal using a diffraction grating of
l
and a spectral resolution of 0.3 cm−1. The laser
2, 400 mm
power was limited to <0.2 mW in order to avoid heating of
the sample.
Figure 13 depicts the temperature distribution along the
shuttle, measured at equally distributed points as marked in
the picture, embedded in the top right of the Figure. The
data is provided by Raman spectroscopy, infrared imaging
and simulation.
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All methods proof the tendency of decreasing temperatures along the shuttle from the heating area towards the
pointer. However, the non-uniform development of the
graphs must be commented on. Here the data obtained by
infrared tomography should be considered as most accurate. On top of the shuttle only silicon is visible to the infrared camera. As of this, no jumps of the emissivity, caused
by different surfaces, are influencing the data.
Raman spectroscopy, in contrast, is not only capable of
detecting changes in temperature, but is sensitive to internal
stresses as well. The leftmost measurement points shown
in Fig. 13 are very close to the already mentioned thermal
bridge below the arms, which was caused by an imperfect
etching process. As of this, internal stresses could influence
the obtained data. This seems likely, since the obtained data
adapts to the infrared based measurements with increasing
distance to the area where internal stresses are expected.
The explanation of the behavior of the simulated data
seems to be twofold. The model only includes a directional
independent thermal conductivity, causing a to high thermal flux in the area of passive heating, resulting in lower
temperatures. Furthermore the model shown in Fig. 8
does not include all details depicted in Fig. 4. Especially
the additional cooling springs where only approximated in
the boundary conditions of the model, resulting in silently
divergent temperatures at the upper end of the shuttle. Further refinement is needed here in the future.
In Figs. 14 and 15, a measurement along an arm of a
10 armed, I = 75 mA (Is = 7.5 mA per arm) driven TA is
shown. The clearly recognizable jump between the reference temperature of 22 ◦ C, measured on the right anchor of
the thermal actuator, and the first temperature on the arm,
reading 68 ◦ C, compared with the flat increase of the temperature along the arm, proofs the effectivity of the already
mentioned constrictions at the ends of the arms, which are
thermally homogenizing and insulating.
The simulated data, presented in Fig. 15, did not take
the existence of the mentioned thermal bridge into account.
The comparison to the data obtained by Raman spectroscopy indicates again, that the influence of the thermal
bridge is negligible.
The observed maximum peak at 86 ◦ C, yielding a temperature increase of △T = 64 K, could be reproduced
using numerical methods and providing a maximal value of
△T = 78 K on the whole structure. Due to varying emissivity values, the data could not be reproduced using infrared imaging.
6.3 Out of plane deformation of the thermal actuator
White light interferometry is an optical non-contact method
used for surface height measurements on 3-D structures as
MEMS with surface profiles on a micro- and nano-scopic
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Microsyst Technol (2014) 20:1041–1050
Fig. 14 Temperature distribution along an arm of a 10 armed TA,
driven by I = 75 mA (Is = 7.5 mA per arm). Data obtained by
Raman spectroscopy
Fig. 13 Temperature development measured at equally distributed
measurement points along the shuttle of a 10 armed TA using a constant drive of I = 75 mA (Is = 7.5 mA per arm). Data provided by
Raman spectroscopy, infrared imaging and simulation. Measurement
points according the marked position numbers in embedded picture,
top right
scale. All measurements where made using a Zygo
NewView 6300. The white light interferometry was used to
verify not only results of finite element based methods, but
for the verification of process parameters as well. Figure 16
depicts a surface map of the five armed TA.
The originally specified target size for the technology process of the aluminum structures, used for the passive heating of the underlaying bulk silicon, is given by
zAl = 100 nm. Fitting the numerical results to the experimental data, presented in Sect. 6.1 by means of varying
the aluminum thickness, indicates a thickness of the latter of zAl = 80 nm. The white light interferometry verified
zAl = 77 nm.
The main task of a TA is the generation of lateral inplane displacement. Numerical results indicate an out of
plane translation of the whole structure during activity,
which could affect the usability of the TA in the tensile testing platform, as some types of CNTs are sensitive against
out of plane loads.
Considering SWCNTs as mentioned in Sect. 2, positioned over a 1 µm gap, an out of plane deformation of 1 %
can be accepted. In our case, simulation and experiment
prove a deformation below of 10 nm , as shown in Fig. 17.
As this corresponds to a deformation of <1 %, it has not to
be addressed during the further development.
6.4 Lateral displacement of the thermal actuator
The generation of lateral in-plane displacement is the only
task of the presented thermal actuator and can be measured
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Fig. 15 Temperature distribution along an arm of a 10 armed TA,
driven by I = 75 mA (Is = 7.5 mA per arm). Positions as in depicted
in Fig. 14. Data obtained by Raman spectroscopy and simulation
using digital image correlation (DIC). Based on a series
of digital images, obtained using an optical microscope,
depicting the thermal actuator in relaxed, not powered
state and under various drives, the displacement of the TA
can be calculated based on a pixel shift. The field of pixels,
used for the calculation of the displacement is shown in
Fig. 18.
The displacement measurements were performed using
an actuator, those arms were entirely etched free, allowing
the actuator to move as expected.
Figure 19 shows the displacement measured using DIC
on a 10 armed TA with 5 ◦ inclined arms compared to data
obtained by simulation. As one can observe, the correlation
is very good indeed.
The requirements presented in Sect. 2 include a displacement of the thermal actuator of more then 1 µm. This can
Microsyst Technol (2014) 20:1041–1050
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Fig. 16 Surface map of a five armed thermal actuator in relaxed state
using a Zygo NewView 6300 white light interferometer
Fig. 19 Lateral displacement of a 10 armed TA with an arm angle of
5 ◦. Data provided by DIC and simulation
Fig. 17 Relative out of plane displacement of the centering shuttle of
a five armed thermal actuator
Fig. 20 Expected lateral displacement of five and 10 armed TA with
an arm angle of 1 ◦ or 5 ◦. Data provided by simulation
7 Conclusions and outlook
Fig. 18 Field of pixels, used for the DIC based lateral displacement
calculations
only be achieved using a TA designed with a small inclination angle of the arms as shown in Fig. 20 or by increasing
the length of the arms compared to the actuators used. Considering the data presented in Fig. 20, the 10 armed thermal
actuator performs slightly better then the five armed version, possibly caused by a higher heat concentration within
the 10 armed structure.
This paper focused on a thermal actuator, designed for the
use in a MEMS tensile testing platform, capable of thermomechanical material characterization on a micro- and nanoscopic scale under different environmental conditions, as
varying temperatures, pressure, moisture or even vacuum.
The goal of the integration of all components into the testing platform is technologically challenging and can be considered as new approach.
The data presented in this paper shows the expected
accordance between simulation and experimentally
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obtained data in the relevant fields of thermal distribution,
lateral movement and out of plane displacement.
Furthermore, the shown results indicate, that the
described thermal actuator is capable of meeting the
requirements formulated before. The successful concept of
an actuator, heated by an aluminum meander on top of an
insulator, provides the specified travel range of more then
1 µm, is within limits regarding out of plane displacement,
is electrically insulated against the other components of the
tensile testing platform and fits seamlessly into the BDRIE
technology process. The match regarding the latter points
allows the full integration with the remaining components,
as displacement and force sensor, into a single chip.
Besides that, the flexible design in combination with
numerical simulations, based on parametrized input files,
allows the integration of an optimized actuator into a wide
range of layouts and enables us to follow our specimencentered approach.
During an intermediate step in the development, the
thermal management with respect to air and vacuum has to
be further optimized.
After having reached this decisive milestone in the
development towards a universal MEMS-based testing platform for heterogeneously bottom-up integrated nanofunctional elements, the focus is now directed in designing and
testing further MEMS components of the platform, such as
a newly developed piezoresistive force sensor, capable of
detecting forces in a nN range. In combination with the
thermal actuator analyzed here and a capacitive displacement sensor we are going to complete the MEMS tensile
testing platform and present simulated data in comparison
to experimentally obtained data.
Acknowledgments The authors wish to thank the Fraunhofer
ENAS for providing the device used for the white light interferometry
and Marco Meinig, who supported the authors during the work at the
device. Finally the authors wish to thank the Deutsche Forschungsgemeinschaft, DFG, for the financial support within the research unit
1713 “Sensoric Micro- and Nanosystems”.
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