Are you working to optimize the performance of your MEMS device? Learn how Polytec's latest technology is used for characterization MEMS devices in cutting edge applications. Our tools for analysis and visualization of structural vibrations of MEMS feature laser vibrometry for measurement of out-of-plane motion with resolution down to picometers and bandwidth out to MHz. Scanning measurements provide full-field mapping and 3D visualization of deflection shapes. By adding stroboscopic video microscopy, we are able to extend our measurement capability to the in-plane direction for complete 3D motion analysis. We present several real-world application studies where our tools have been instrumental in the design and development of MEMS. We invite you to join this web presentation to find out what Polytec can do for you.

1. Improving Performance of MEMS Designs
Using Dynamic Characterization
Advancing Measurements by Light • www.polytec.com 1

2. Polytec Introduction
Eric Lawrence
MEMS Business Development
Manager
Advancing Measurements by Light • www.polytec.com 2

3. Contents
Introduction to Laser Vibrometry
•Polytec Micro System Analyzer (MSA-500)
•Application: MEMS Comb Drive
•Application: MEMS mmirror
•Application: MEMS / NEMS Cantilever
•Application: Wafer Level Testing Pressure Sensor
•New Ultra High Frequency Vibrometer

4. Optical Measurement Solutions
Laser Doppler Vibrometers
For non-contact vibration
measurements
Laser Surface Velocimeters
For surface speed and length
measurements
White Light Interferometers
For surface topography
measurements
Advancing Measurements by Light • www.polytec.com

5. Tools for Vibration Analysis
Polytec Scanning Vibrometer
Data Storage Fast, accurate
visualization and
analysis of structural
vibration
MEMS Automotive
Health Monitoring
Aerospace
Micro Electro Mechanical
Structures (MEMS)

6. Challenges and Requirements for MEMS Testing
Diverse tools available to measure wide range physical properties
(shape, dimension, film thickness, time response, stress, roughness,
stiction, resonant frequency, environmental response…)
High spatial resolution, accuracy and precision required
Fast response times often require high speed measurement
techniques
Spatial complexity (mm – nm) of MEMS challenging for conventional
techniques
Wide range of performance criteria among different devices
Handling and environmental requirements
Fast measurement speed is critical for high volume production testing
Reliable techniques that allow scientists and engineers to effectively
communicate physical properties

7. Motivation
Why optical measurement of MEMS dynamics?
MEMS usually involve active moving elements for sensing and
actuation
Electrical test can prove if a device is working or not, but……
Electrical testing can’t determine exact behavior of device
Need highly sensitive, non-invasive , real-time measurement
 Laser Doppler Vibrometry

8. Laser Doppler Vibrometry
Measurement Beam
f0
f0 ± fD Bragg cell
Reflected Beam He-Ne Laser
<1mw (633nm)
x(t)
v(t) f0 + 40 MHz
Photo-detector
Frequency Modulated
signal
40 MHz ± fD
Δ fD = 2V/λ

9. Laser Doppler Vibrometry
Signal Demodulation
FM Doppler signal Controller
Photo-detector system
Voltage ~
Velocity
AM electrical signal FFT Spectrum
Voltage ~
Displacement

10. Scanning Laser Doppler Vibrometer
The interferometer is coupled via a fiber into the microscope (MSA)
A scanning mirrors allows to scan the whole surface point by point

11. Scanning Laser Doppler Vibrometer
Vibration Time Signal
sequential measurement at all
points. Excitation for all points
Vibration Spectrum

12. Advantages of Laser Doppler Vibrometer
• Real Time Measurement: Fast signal-based measurements from
broadband excitation, can measure transient response
• High Resolution: Displacement resolution down to picometer
• High lateral resolution: Laser spot focused down to 700 nm
• High frequency bandwidth: DC to 24 MHz (1.2 GHz)
• High accuracy: Doppler technique highly accurate and linear
• Can do difficult measurements on range of materials, under
required environmental conditions, i.e. thru glass into a vacuum
chamber,  calibration independent of these factors
• Probe Station Integration: Integrates with commercially available
probe stations for wafer level testing
Advancing Measurements by Light • www.polytec.com

13. In-plane: Strobe Video Microscopy
Additional Strobe Video Microscopy
Capability for in-plane motion
In-Plane motion of MEMS
Comb drives
Gyroscopes
Accelerometers
Automatically acquires strobe image sets
Pattern Matching to measure displacement
Software tools for analyzing response

14. Topography: White Light Interferometry
Additional Topography Measurement Capability
Topographical Measurement of:
Step-Height
Shape (Curvature, Flatness)
Roughness
Form Parameters (Dimensions,
Angle, Radius)

15. MSA-500 Micro System Analyzer
Combines powerful tools for precise 3D
analysis of structural vibration and
surface topography:
•Scanning Laser Vibrometry for fast measurement
and 3D visualization of out-of-plane deflection
shapes.
•Strobe Video Microscopy for capturing and
analyzing in-plane motion.
•White Light Interferometry for mapping surface
topography.

16. Applications
Advancing Measurements by Light • www.polytec.com

17. Example: Comb Drive Resonator
In-plane actuator
driven by electrostatic
pulling force
1 nh 2
F ε V
2 g
Restoring force from
bifold springs
Substituting for Keff and Meff:
Natural Frequency
E w3 (1 2 )
given by: d  rL3A eff
0  K eff
M eff
Where E is Young’s Modulus of Elasticity, w is
spring width, r is the density, L is the spring
length and Aeff is the effective area of comb drive.

18. Example: Comb Drive Resonator
Setup:
Measurements were performed with MSA system at our lab in
Tustin, CA
Device + Fixture placed under microscope and positioned into place
Relatively easy setup for placing chip and locating P6 Comb Drive to
be measured
Vibration Isolated Table to minimize background motion
Device driven from built-in waveform generator and amplifier

19. Example: Comb Drive Resonator
Frequency Response:
Set up a grid of approximately
700 measurement points
80 Volt Burst Chirp Excitation
to 2 MHz, 25600 Lines FFT
Measurement time each spot
12.8 ms (chirp response)
Frequency Response Function
measured for each point
Automatically Scan
measurement for all points
F1 =.0138 MHz
0.407 MHz 0.527 MHz 0.929 MHz 1.345 MHz
0.453 MHz 1.614 MHz
0.344 MHz 1.169 MHz 1.493 MHz
0.590 MHz

20. Example: Comb Drive Resonator
1610 KHz
13.8 KHz
Operational
Deflection shapes
Resonance
526 KHz displayed for each
frequency peaks
frequency graphical
selected by
corresponds to a
interface tool
unique mode

21. Example: Comb Drive Resonator
Fundamental rigid body resonance at 13.8 KHz

22. Dynamic Response of Mirror Array
Courtesy Rick Oden, Texas Instruments
•Settling time dynamics of whole
mirror (3D image of time
sequence)scanning vibrometry
•Because the heart of the projector
system is the DMD mirror array – a Hinge
thorough understanding of the Axis
dynamic motion of the mirrors is
critical to gauge performance of
current as well as future
Tilt Motion Direction
technology directions…

23. Example: Texas Instruments mdisplay
• Hermetically sealed Micro-opto-electro-
mechanical system(MOEMS)…
• Massive array of 16mm (older) or 12.7mm
mirrors are
used as light deflectors (modulators)…
• Arrays up to 2.2 million mirrors are currently in
production…
• Each mirror has a hidden hinge over which
it twists upon…
• Tilts of the pixels are ±10 or ±12 degrees…
Yoke/Beam Hinge Post
Mirror (support)
Hinge
Spring Tips
Drive 23
Electronics and Interconnects…

24. Example: Texas Instruments mdisplay
• System focuses laser spot through
microscope objective onto surface of
interest…
• Reflected laser spot is sent to the
interferometer to compare against for
Doppler frequency shift…
• For this optical set-up, the minimum
beam waist for the laser signal is
approximately 1mm.
Hinge Axis
(pivot axis)

25. Example: Texas Instruments mdisplay
Hinge Axis
(pivot axis)
• As mirror transitions from one state to
another(‘-’ to ‘+’ for example), the MSA
system can acquire a time domain response of
this point on the mirror…

26. Example: Texas Instruments mdisplay
Hinge Axis
(pivot axis) • As we all know – three points are
necessary to determine a plane. Similarly,
to build up a time development of the
mirror – several points must be inspected
over the mirror to render reliable
data…

27. Example: Texas Instruments mdisplay
Hinge
Axis
• There are three primary directions
Tilt Motion Direction
of motion that characterize these
micro-mirrors…
• With these three base motions in
mind, MatLab is used as a processing
and graphical user interface (GUI)
Roll Motion Direction
to obtain the time developed
dynamics of the mirrors…
Sag Motion Direction 27

28. Example: Texas Instruments mdisplay
• The base motion directions above are shown for a single
mirror. Ability is implemented to acquire and process data on
several mirrors to provide dynamics where we can compare
results mirror-to-mirror…
28

29. Example: Texas Instruments mdisplay
• Image above (left)
shows one of the
processing/visualization
windows within
MatLab.
• In this case, a (3x3)
array of mirrors are
shown with their
corresponding tilt, roll
and sag axis time
developed dynamics in
the right side of figure.
29

30. Example: Cantilever
Model for Modal Response of Cantilever based on
mechancial parameters
Properties
Length X 0.225 mm
Width 3.5e-002 mm
Thickness 4.e-003 mm
Material Si
Volume 3.15e-005 mm³
Mass 7.308e-011 kg
Nodes 988
Elements 900

31. Example: Cantilever
Base Excitation:
Cantilever + Substrate
Piezo used to provide external

base excitation, transmitted
directly to cantilever
Excited from built-in waveform
 Piezo
generator Actuator
Picma Piezo from Physik Instrumente
Part # Dimensions Max. Blocking Resonant
AxBxL displacement force [N @ frequency
[mm] [µm @ 120 V] 120 V] [kHz] ±20%
P-883.10 3x3x9 8 ±20% 290 135
More info at: http://www.physikinstrumente.com

32. Example: Cantilever
Frequency Response:
Swept sine Measurement laser spot directed at
measurement to the end of the cantilever
2000 KHz
Measurement time
each spot 12.8
milliseconds (chirp
response)
Frequency Response
Function measured
for each point

33. Example: Cantilever
1st Bending Mode: Discrepancy: -29%
Experimental Data: Model:

34. Example: Cantilever
2nd Bending Mode: Discrepancy: -23%
Experimental Data: Model:

35. Example: Cantilever
Torsion Mode: Discrepancy: -49%
Experimental Data: Model:

36. Example: Cantilever Array
Measurement on poly3 400 um
cantilever showing resonance at
18.45 KHz and damping factor
0.10 (squeeze film damping)

37. Example: Wafer level testing
PARTEST: Testing Methods for Determination of Production Relevant
Parametersin MEMS on Wafer Level
http://www.memunity.org/par-test.htm

38. Example: Wafer level testing
Electrostatic Electrodes
Elctrostatic Excitation • No mechanical contact to wafer
• Force applied to conductors,
semiconductors and dielectric
materials
• Realized –3 dB frequency bandwith
300 kHz
• Integrated distance measurement
• Wafer level test possible
• Electrodes transparent (ITO)
Micropositioner Probe „card“

39. Example: Wafer level testing
• Pressure sensors with quadratic membrane  regular dies
have the 2nd/3rd mode at the same frequency values
-4
x 10
4
3
v [m/s]
2
1
0
0 200 400 600 800 1000
f [kHz]

40. Example: Wafer level testing

41. Example: Wafer level testing
mean( EIE) = 0.08µm
std( EIE) = 0.04µm
0.25
Wafer map with
Classification 0.2
EIE [µm]
0.15
0.1
0.05
Peak error
max. EIE
Red spots show bad dies EIE: Estimated Identification Error

42. UHF-120 Ultra High Frequency Vibrometer
42

43. Ultra High Frequency Vibrometer
Technical Specifications UHF-120

44. Ultra High Frequency Vibrometer
Example: SAW Filter Measurement

45. Ultra High Frequency Vibrometer
Example: SAW Filter 262 MHz

46. Conclusion
• Polytec MSA unique, all-in-one optical
measurement solution for 3D vibration
measurement plus topography
measurement
• Real-time, broadband measurement
with frequency response in milliseconds
• Highly Sensitive measurement with
resolution down to picometer level
• Well supported by engineers
knowledgeable with MEMS applications
and necessary requirements for testing
Advancing Measurements by Light • www.polytec.com