Mary Coan
April 6th 2010
Outline

How it all began…
 Nanoelectromechanical Systems (NEMS)
Basic Properties
 Typical Problems
 Fabrication Processes
 Application of NEMS
 Conclusion

How it all began…

1959-Richard Feynman offered a prize of $1000 "to the first guy who
makes an operating electric motor - a rotating electric motor which can
be controlled from the outside and, not counting the lead-in wires, in
only 1/64 inch cube."
 stimulate new fabrication technology

1960-Bill McLellan, using amateur radio skills, built the motor with his
hands using tweezers and a microscope
 2000 rpm motor weighed 250 micrograms
 13 parts
Nanochamber ultrafast gas sensing
with NEMS resonators
http://www.nanowerk.com/spotlight/spotid=2431.php
Image 1: http://nano.caltech.edu/gallery/group2.html
Nanoelectromechanical Systems (NEMS)

In the 50 years since The field of microelectromechanical systems (MEMS)
caught up with Feynman's bet
 achieved commercial production capabilities of motors
many times smaller

NEMS
 devices integrating electrical and mechanical
functionality on the nanoscale

Research on building functional nanoscale
Colorized
SEM image
Ultra underway
electromechanical
systems
isofwell
http://www.svtii.com/files/MEMS-NEMS-SVTI.pdf
Image 1: http://nano.caltech.edu/gallery/group2.html
High Fequency NEMS resonator
Nanoelectromechanical Systems (NEMS)
Used in aerospace, automotive, biotechnology,
instrumentation, robotics, manufacturing and other
applications
SEM image of two Single Cell Pico Force
SEMsensors
- nanocantilever resonator
Microscopy force
 Many functions
gas sensor

 Sensing
 Actuation
 Communication
http://www.svtii.com/files/MEMS-NEMS-SVTI.pdf
Image 1&2: http://nano.caltech.edu/gallery/group2.html
http://www.kschwabresearch.com/articles/detail/11
Nanomechanics coupled
to superconducting
microwave resonators
Outline

How it all began…
 Nanoelectromechanical Systems (NEMS)
Basic Properties
 Typical Problems
 Fabrication Processes
 Application of NEMS
 Conclusion

Basic Properties

Two principal components common to most
electromechanical systems
 Mechanical element
○ Either deflects or vibrates in response to an applied force
○ Used to sense static or time-varying forces
 Transducers
○ Convert mechanical energy into electrical or optical signals
and vice versa
○ Input transducer simply keeps the mechanical element
vibrating steadily while its characteristics are monitored as
the system is perturbed
http://www.nanowerk.com/spotlight/spotid=2431.php
Image 1: http://palasantzas.fmns.rug.nl/NEMS.html
Basic Properties

Attain extremely high fundamental frequencies
 mechanical responsitvity

Dissipate very little energy
 Characterized by the high quality or Q factor of
resonance

Extremely sensitive to external damping
mechanisms
 Crucial for building many types
of sensors
 Suppression of random
mechanical fluctuations
○ Highly sensitive to applied forces
http://www.nanowerk.com/spotlight/spotid=2431.php
http://palasantzas.fmns.rug.nl/NEMS.html
Image1: http://phycomp.technion.ac.il/~phr76ja/boston/what2.html
Outline

How it all began…
 Nanoelectromechanical Systems (NEMS)
Basic Properties
 Typical Problems
 Fabrication Processes
 Application of NEMS
 Conclusion

Typical Problems

Great promise as highly
sensitive detectors
 mass, displacement, charge,
and energy
An efficient, integrated, and customizable
technique for actively driving and tuning NEMS
resonators has remained elusive
 Electromechanical devices are scaled downward

 transduction becomes increasingly difficult
○ Causing the creation of finely controlled integrated
systems to fail
http://www.nanowerk.com/spotlight/spotid=2431.php
Image1: http://phycomp.technion.ac.il/~phr76ja/boston/what2.html
Typical Problems

Resonator sizes continue to decrease to the
nano-scale
 Surface to volume ratio increases
○ Susceptible to a variety of surface related noise
mechanisms
 Such as gas molecules impinging the surface, loss due to
defects and impurities, scattering of surface acoustic waves
by roughness

Surfaces contribute the most to energy
dissipation in NEMS
 detailed
understanding is still missing
Nanoscale resonators exert relatively strong forces on tiny
particles, leading the way to important advancements in
MEMS and MOMS systems
http://www.nanowerk.com/spotlight/spotid=2431.php
http://www.gizmag.com/nanoscale-light-resonator/13401/picture/105479/ Image 1
Typical Problems

Casimir Effect
 quantum mechanical force that attracts objects a few
nanometers apart
 Very Strong Force
○ Hard to control
devices

Efficient actuation
creation of mechanical
motion by converting
various forms of energy
MEMS setup used to detect the
rotating or linear
presence of Casimir force.
mechanical energy

http://www.semiconductor.net/article/444199-Scientists_to_Conquer_Casimir_Effect_Enable_NEMS.php
Typical Problems

Fabrication
 Scale down effects
○ Lithography
 Wave length limitations
 Integration with typical CMOS processes

Mass Production
 Packaging
○ Fragile
 Cost
Top Image: http://www.texmems.org/
Bottom Image: http://www.nems.se/nimble.html
Outline

How it all began…
 Nanoelectromechanical Systems (NEMS)
Basic Properties
 Typical Problems
 Fabrication Processes
 Application of NEMS
 Conclusion

Fabrication Processes

Basic Steps of Silicon Micromachining:
 Lithography
 Deposition of sacrificial and structural layers (PECVD,





evaporation, sputtering)
Removal of Material (patterning)
Selective etching (RIE, Laser)
Doping
Bonding (Fusion, anodic)
Planarization
MEMS and NEMS: systems, devices, and structures Nano- and microscience, engineering, technology, and medicine series By: Sergey Edward Lyshevski
Image: http://hello-engineers.blogspot.com/2009/04/mems-fabrication-assembling-and-packing.html
Fabrication Processes
UV Light
Mask
Photo
Resist
Mask
Photo Resist
Photo Resist
Sacrificial Layer
Sacrificial
(SiO2)Layer
Substrate (Silicon Wafer)
Surface Micromachining and
sacrificial layer technique
http://iopscience.iop.org/0964-1726/10/6/301/pdf/sm1601.pdf?ejredirect=migration
Animated Version
Fabrication Processes
UV Light
Photo Resist
(100) Silicon Wafer P+ Si
SiNx
Bulk Micromachining along
crystallographic planes
http://iopscience.iop.org/0964-1726/10/6/301/pdf/sm1601.pdf?ejredirect=migration
Animated Version
Fabrication Processes
Left image: http://www.memx.com/
Right Image: http://www.npl.co.uk/science-+-technology/nanoscience/surface-+-nanoanalysis/mems-particle-detector
Outline

How it all began…
 Nanoelectromechanical Systems (NEMS)
Basic Properties
 Typical Problems
 Fabrication Processes
 Application of NEMS
 Conclusion

Application of NEMS:
NEM switched Capacitor

Demand for increased information storage
 Pushed silicon technology to its limits
 Research involving novel materials and device
structures
○ Magnetoresistive random access memory
○ Carbon nanotube field-effect transistors

NEM switched capacitor structure
 Vertically aligned multiwalled carbon nanotubes
○ mechanical movement of a nanotube relative to a carbon
nanotube based capacitor defines ‘ON’ and ‘OFF’ states

Impossible to control the number and spatial
location of nanotubes over large areas
JAE EUN JANG, et. al . “Nanoscale memory cell based on a nanoelectromechanical switched capacitor” Nature Vol 3 January 2008 doi:10.1038/nnano.2007.417
Application of NEMS:
NEM switched Capacitor

Carbon Nanotube Fabrication:
 Grown with controlled dimensions at pre-defined
locations on a silicon substrate
○ Compatible with existing silicon technology
○ Vertical orientation allows for a significant decrease in cell
area over conventional devices
JAE EUN JANG, et. al . “Nanoscale memory cell based on a nanoelectromechanical switched capacitor” Nature Vol 3 January 2008 doi:10.1038/nnano.2007.417
Application of NEMS:
NEM switched Capacitor
JAE EUN JANG, et. al . “Nanoscale memory cell based on a nanoelectromechanical switched capacitor” Nature Vol 3 January 2008 doi:10.1038/nnano.2007.417
Application of NEMS:
NEM switched Capacitor

Data has been written to the structure
 Theoretically it is possible to read data with
standard dynamic random access memory
sensing circuitry

Simulations have been completed
 high-k dielectrics instead of SiNx
○ increase the capacitance to the levels needed
for dynamic random access memory
applications
JAE EUN JANG, et. al . “Nanoscale memory cell based on a nanoelectromechanical switched capacitor” Nature Vol 3 January 2008 doi:10.1038/nnano.2007.417
Application of NEMS:
Self Sustaining NEM oscillator

Sensors based on nanoelectromechanical systems
vibrating at high and ultrahigh frequencies
 capable of levels of performance that surpass those of larger
sensors

NEM devices have achieved unprecedented
sensitivity
 Displacement, mass, force and charge detection

Passive devices
 Require external periodic or impulsive stimuli to excite them
into resonance

Novel autonomous and self-sustaining NEM oscillator
 Generates continuous ultrahigh-frequency signals when
powered by a steady d.c. source
X.L. Feng, et.al. “A Self Sustaining Ultrahigh-frequency nanoelectromechanical oscillator” Nature Vol 3 June 2008 doi:10.1038/nnano.2008.125
Application of NEMS:
Self Sustaining NEM oscillator

A self-sustaining ultra high frequency NEM
oscillator
 Frequency determining element in the oscillator is a
NEM resonator
○ Embedded within a tunable electrical feedback network to
generate active and stable self-oscillation
 Excellent frequency stability
 Linewidth narrowing and low phase noise performance
X.L. Feng, et.al. “A Self Sustaining Ultrahigh-frequency nanoelectromechanical oscillator” Nature Vol 3 June 2008 doi:10.1038/nnano.2008.125
Application of NEMS:
Self Sustaining NEM oscillator
Dc=source voltage to increase the
ac current volatage
Amplifier is amplifing the voltage
from the phase controlled current
The resonator is filtering the
current, allowing for only a certain
freq to go through
H(jw) is a freq response
Control changes the phase
X.L. Feng, et.al. “A Self Sustaining Ultrahigh-frequency nanoelectromechanical oscillator” Nature Vol 3 June 2008 doi:10.1038/nnano.2008.125
Application of NEMS:
Self Sustaining NEM oscillator
Ultrahighfrequency oscillators provide a
comparatively simple means for
implementing a wide variety of practical
sensing applications
 Opportunities for nanomechanical
frequency control, timing and
synchronization

X.L. Feng, et.al. “A Self Sustaining Ultrahigh-frequency nanoelectromechanical oscillator” Nature Vol 3 June 2008 doi:10.1038/nnano.2008.125
Application of NEMS:
NEM Tunable Laser

Tuning the frequency of an oscillator is of critical
importance
 Fundamental building block for many systems
○ Mechanical or Electronic

Highly inadequate in optical oscillators
 Particularly in semiconductor laser diodes

Limitations in tuning a laser frequency (or wavelength)
 include the tuning range and the speed of tuning
○ Typically milliseconds or slower

Tuning is often not continuous
 Requires complex synchronization of several electrical
control signals
M.C.Y. Huang et.al “A Nanoelectromechanical tunable laser” Nature Vol 2 March 2008 doi:10.1038/nphoton.2008.3
Application of NEMS:
NEM Tunable Laser

Nanoelectromechanical Tunable Laser
 Lightweight NEM mirror based on a single-layer, high
contrast grating (HCG)
○ Enables a drastic reduction of the mirror mass
○ Increases the mechanical resonant frequency
○ Increases the tuning speed
 Allows a wavelength-tunable light source
○ Potential switching speeds of the order of tens of
nanoseconds
○ Various new areas of practical application
 bio- or chemical sensing, chip-scale atomic clocks and projection
displays
M.C.Y. Huang et.al “A Nanoelectromechanical tunable laser” Nature Vol 2 March 2008 doi:10.1038/nphoton.2008.3
Application of NEMS:
NEM Tunable Laser


Schematic of the
electrostatic-actuated
NEMO-tunable VCSEL
High Contrast Grating
(HCG) is freely
suspended above a
variable air gap
 Supported by a
nanomechanical structure
○ cantilever
○ Bridge
○ folded beam
○ membrane
M.C.Y. Huang et.al “A Nanoelectromechanical tunable laser” Nature Vol 2 March 2008 doi:10.1038/nphoton.2008.3
Application of NEMS:
NEM Tunable Laser

Integration of the freely suspended HCG mirror with a
variety of nanomechanical actuators that can be designed
for different values of mechanical stiffness
M.C.Y. Huang et.al “A Nanoelectromechanical tunable laser” Nature Vol 2 March 2008 doi:10.1038/nphoton.2008.3
Application of NEMS:
NEM Tunable Laser

Wavelength tuning is a
function of the air-gap
thickness below the NEM
suspended HCG

Blue Triangle Curves
 Calculated laser emission
wavelength (Wavelength)

Color-coded Contour
 HCG mirror reflection
bandwidth (Reflectivity)
M.C.Y. Huang et.al “A Nanoelectromechanical tunable laser” Nature Vol 2 March 2008 doi:10.1038/nphoton.2008.3
Outline

How it all began…
 Nanoelectromechanical Systems (NEMS)
Basic Properties
 Typical Problems
 Fabrication Processes
 Application of NEMS
 Conclusion

Conclusion
Nanoelectromechanical systems (NEMS) are used to
measure extremely small masses and forces
 Measurements rely on a resonator oscillating at a
very stable frequency so that a small change in the
resonant frequency caused by, for example, a
molecule landing on the resonator, can be readily
detected
 Self-sustaining NEMS oscillators enable a wide
spectrum of applications

 Offer significant advantage over other frequency-shift
detection as no source of external excitation is required
 Yields an immense simplification of design that is crucial for
next-generation, highly multiplexed sensing applications
involving large arrays of devices
Conclusion

A viable structure and fabrication process for a NEM
memory cell for ultra-large-scale integrated memory
applications
 Proposed write–read scheme is similar to that of a conventional
DRAM
○ Conventional sensing schemes
○ CMOS circuits
○ High integration densities due to the vertical nature of the NEM
capacitor

High-speed nanoelectromechanical tunable laser
 Monolithically integrating a lightweight, single-layer HCG as the
movable top mirror
 results in a drastic reduction in mass
 substantial improvement in tuning speed
 Results in an optical mirror design for the next generation of
NEMO-tunable devices
G3
Rebuttal: Nanoelectromechanical Systems
NMEs
Mary Coan
Rebuttal
• There were several comments on the lack of information
regarding the physics behind how NEMs work
– I chose not to go into great depth about the physics behind
these devices due to the audience
• I understand that there are graduates in the class however the
majority of the class are undergraduates who have never been in
contact with this subject matter before
– An example of how the mechanical process of the device
worked using an animation would have been helpful
– An overview of the current technology (MEMS) may also
have been added
• I left out certain information regarding the process of
some of the example covered due to the time
constraints and the level of expertise needed to fully
understand
Rebuttal
• In regards to the organization of the presentation,
NEMS is a very broad topic with many different
applications, processes (new and old) and types
devices due to time constraints I could not mention
all of the information
– I chose to keep the presentation simple for the sake of
the majority of the audience
– I understand that the graduates in the class may have
prior knowledge of NEMS and such a simplified
presentation may not be enough information for them
• I believe I spoke about the different applications of
the sensors in class and showed images of them
throughout the presentation
Rebuttal
• I am not sure how the cantilever beam was not well
depicted
– There was an example of how to form a cantilever beam
– I did not go to into detail about the cantilever beam
because it is an older technology and I was trying to
focus on newer NEMS technologies
• In regards to NEMS “wearing out” and stiction
problem, they do. Different types of materials are
being looked into to help with this problem.
• As of today NEMS, as far as I know, NEMS are not
massively produces like Si based chips because of the
variation issues.
– They are produced on smaller sized wafers instead of
the larger ones to help with this issue
Rebuttal
• Thank you for all of the comments I will
try to take them into account for future
presentations I have to give.
G1
Review : Nanoelectromechanical Systems
(NMEs)
Edson P. Bellido Sosa
The presenter explained some of the basic concepts related to NEMS in general terms.
However, she did not explain the physics behind those process that would have been
helpful to understand how the transducer and the mechanical works. She explain some of
the problems of this technology but the explanation of the Casimir effect was not clear. She
mention some fabrication process and explain one process.
http://cdn.physorg.com/newman/gfx/news/hires/khatibmems.png
The paper about NEM switched Capacitor was very
interesting. However, some of the details about the
fabrication were not clear for instance how they
position the carbon nanotubes? and how they do
the SiN coating? Was it by e-beam lithography?
Open questions about the paper are: how easily is
to reproduce the results of the device? and is it
possible to achieve large scale integration of these
devices?
The paper about NEM Tunable Laser looks interesting but
she did not explain clearly how the device works. She
showed the capabilities of the device and the design and
images of the device. However she did not explain which
role play the different parts of the device.
As further research, I consider that work in large scale
integration of NEMS is needed. Also research in bio-NEMS
for uses in disease diagnosis and biological weapon sensor.
http://www.boulder.nist.gov/div853/MRD_Groups/MRD_Projects/Bi
oMEMS_cell_puller.jpg
G2
Review : Nanoelectromechanical Systems
(NMEs)
Alfredo Bobadilla
NEMS lecture review
The theme was not well organized. It should have been emphasized the different
novel methods enabling NEMS development, i.e. laser micromachining for 3D structures,
DRIE for high aspect ratio structures, soft lithography for biocompatible devices, etc.
The essence of different working principles used for NEMS sensors and actuators should
have been mentioned, i.e. thermal, electrical, piezolectric, piezoresistive, magnetic
and electrostatic.
Essential electrical and mechanical concepts such as stress & strain and resonant
frequency & quality factor were not illustrated.
The cantilever beam was not correctly illustrated when it was mentioned on applications
for chemical sensing or mass spectrometry, it was not explained what factors contribute
to getting a high sensitivity to mass or pressure.
The cantilever beam is the basic element for a broad range of applications and its basic
working principle was neither well depicted.
Alfredo D. Bobadilla
G4
Review : Nanoelectromechanical Systems
(NMEs)
Diego A. Gómez-Gualdron
Nano-electro-mechanical Systems
 The logic reduction-sizie step on microelectronical
devices
Features
• Nanoscale size
• Transduction of a mechanical
stimuli into a signal
Berkeley Lab (www.lbl.gov)
• Two basic elements:
a) Mechanical part
b) Transductor
In the example above, the nanotube is connected to an electrode. The nanotube is
made vibrate at certain frequency, but this changes as atoms impinge onto the
nanotube. The change in frequency is converted in an electrical signal that relates to
the weight of detected atoms
Review
• There was a good amount of graphics and information in the
slides. The animation made for the fabrication process was
very good
• A fairly number of applications and examples was shown,
corresponding to several recent (2008-present) high-impact
publications
• The speaker looked confident, coherent, and in general made
a good oral presentation
Review
• Perhaps, the execution of the introduction could improve.
Although, I realize the ‘Basics’ sections is present, there is certain
elements that would have deserved more emphasis:
a) The working (elementary) principle of the NEMS in sensing,
actuation and communication.
b) An overview to the current technology (MEMS). It would be
easier to understand the goals of NEMS, if one understands how
the currently technology works in several applications
• The ‘history’ slides that open the presentation rises the expectation
of a talk about nano-sized motors, but the topic covered is more of
mechanical responses converted in signals. A more suited example
should be used to open up
G5
Review : Nanoelectromechanical Systems
(NMEs)
Norma Rangel
Nanoelectromechanical Devices,
by Mary Coan
• Mary did a good job in her presentation, she gave
a fair introduction of MEMs, their properties and
they work. She also mentioned the drawbacks of
NEMs and fabrication processes.
• Even though Mary mentioned applications of
NEMs more details in state of the art could have
been shown.
• Mary was very fluent, and gave a good talk, the
only thing missing in my opinion was the further
research needed in this topic, and a little bit more
fluently when answering questions.
G6
Review : Nanoelectromechanical Systems
(NMEs)
Jung Hwan Woo
• I believe that MEMS/NEMS devices have
longevity problems as nano-structures tend to
“wear out” pretty fast. How is this being
resolved?
• Another problem with MEMS devices is the
stiction problem during and following the etch of
sacrificial layer. How are people addressing this
issue?
• How do manufacturers batch fabricate NEMS
devices and maintain the same
physical/electrical/thermal properties? In such
small scale, the variation of properties that
moving parts have could be very large.