improving performance of mems using dynamic characterizaton
DESCRIPTION
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.TRANSCRIPT
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Advancing Measurements by Light • www.polytec.com 1
Improving Performance of MEMS Designs
Using Dynamic Characterization
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Eric Lawrence MEMS Business Development
Manager
Advancing Measurements by Light • www.polytec.com 2
Polytec Introduction
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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
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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
Optical Measurement Solutions
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Fast, accurate visualization and analysis of structural vibration
Automotive
Health Monitoring
MEMS
Aerospace
Data Storage
Polytec Scanning Vibrometer
Tools for Vibration Analysis
Micro Electro Mechanical
Structures (MEMS)
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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
Challenges and Requirements for MEMS Testing
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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
Motivation
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Frequency Modulated signal
40 MHz ± fD
Bragg cell f0 ± fD
f0
f0 + 40 MHz
He-Ne Laser <1mw (633nm)
x(t) v(t)
Photo-detector
Measurement Beam
Reflected Beam
Δ fD = 2V/λ
Laser Doppler Vibrometry
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Voltage ~
Velocity
Voltage ~
Displacement
FM Doppler signal
AM electrical signal
Controller Photo-detector system
FFT Spectrum
Signal Demodulation
Laser Doppler Vibrometry
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The interferometer is coupled via a fiber into the microscope (MSA)
A scanning mirrors allows to scan the whole surface point by point
Scanning Laser Doppler Vibrometer
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sequential measurement at all points. Excitation for all points
Vibration Time Signal
Vibration Spectrum
Scanning Laser Doppler Vibrometer
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Advantages of Laser Doppler Vibrometer
Advancing Measurements by Light • www.polytec.com
• 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
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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
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Topography: White Light Interferometry
Additional Topography Measurement Capability
Topographical Measurement of:
Step-Height
Shape (Curvature, Flatness)
Roughness
Form Parameters (Dimensions,
Angle, Radius)
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Combines powerful tools for precise 3D
analysis of structural vibration and
surface topography:
MSA-500 Micro System Analyzer
•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.
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Applications
Advancing Measurements by Light • www.polytec.com
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In-plane actuator driven by electrostatic pulling force
Restoring force from
bifold springs
Natural Frequency
given by:
Substituting for Keff and Meff:
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. eff
eff
M
K
0
eff3
23
AL
)1( wE
r
d
2
2
1V
g
nhεF
Example: Comb Drive Resonator
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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
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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
0.344 MHz
0.407 MHz
0.453 MHz
0.527 MHz
0.590 MHz
0.929 MHz
1.169 MHz
1.345 MHz
1.493 MHz 1.614 MHz
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Example: Comb Drive Resonator
1610 KHz
13.8 KHz
526 KHz Resonance frequency peaks selected by graphical interface tool
Operational Deflection shapes displayed for each frequency corresponds to a unique mode
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Fundamental rigid body resonance at 13.8 KHz
Example: Comb Drive Resonator
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•Settling time dynamics of whole
mirror (3D image of time
sequence)scanning vibrometry
Tilt Motion Direction
Hinge
Axis
•Because the heart of the projector system is the DMD mirror array – a thorough understanding of the dynamic motion of the mirrors is critical to gauge performance of current as well as future technology directions…
Dynamic Response of Mirror Array Courtesy Rick Oden, Texas Instruments
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• 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…
Mirror
Hinge
Hinge Post (support)
Yoke/Beam
Drive Electronics and Interconnects…
Spring Tips
Example: Texas Instruments mdisplay
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Hinge Axis
(pivot axis)
• 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.
Example: Texas Instruments mdisplay
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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…
Example: Texas Instruments mdisplay
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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…
Example: Texas Instruments mdisplay
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Tilt Motion Direction
Hinge
Axis
Roll Motion Direction
Sag Motion Direction
• There are three primary directions
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) to obtain the time developed dynamics of the mirrors…
Example: Texas Instruments mdisplay
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• 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…
Example: Texas Instruments mdisplay
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• 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.
Example: Texas Instruments mdisplay
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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
Model for Modal Response of Cantilever based on mechancial parameters
Example: Cantilever
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Base Excitation:
Piezo used to provide external base excitation, transmitted directly to cantilever
Excited from built-in waveform generator
More info at: http://www.physikinstrumente.com
Picma Piezo from Physik Instrumente
Resonant
frequency
[kHz] ±20%
Blocking
force [N @
120 V]
Max.
displacement
[µm @ 120 V]
Dimensions
A x B x L
[mm]
Part #
135 290 8 ±20% 3 x 3 x 9 P-883.10
Piezo
Actuator
Cantilever + Substrate
Example: Cantilever
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Frequency Response:
Swept sine measurement to 2000 KHz
Measurement time each spot 12.8 milliseconds (chirp response)
Frequency Response Function measured for each point
Measurement laser spot directed at the end of the cantilever
Example: Cantilever
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1st Bending Mode:
Experimental Data: Model:
Discrepancy: -29%
Example: Cantilever
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2nd Bending Mode:
Experimental Data: Model:
Example: Cantilever
Discrepancy: -23%
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Torsion Mode:
Experimental Data: Model:
Example: Cantilever
Discrepancy: -49%
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Measurement on poly3 400 um cantilever showing resonance at 18.45 KHz and damping factor 0.10 (squeeze film damping)
Example: Cantilever Array
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PARTEST: Testing Methods for Determination of Production Relevant
Parametersin MEMS on Wafer Level
http://www.memunity.org/par-test.htm
Example: Wafer level testing
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Electrostatic Electrodes
• 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“
Elctrostatic Excitation
Example: Wafer level testing
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0 200 400 600 800 10000
1
2
3
4x 10
-4
f [kHz]
v [m
/s]
• Pressure sensors with quadratic membrane regular dies have the 2nd/3rd mode at the same frequency values
Example: Wafer level testing
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Example: Wafer level testing
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mean( EIE) = 0.08µm
std( EIE) = 0.04µm
0.05
0.1
0.15
0.2
0.25
Peak error
max. EIE
Red spots show bad dies
Wafer map with Classification
EIE
[µm
]
EIE: Estimated Identification Error
Example: Wafer level testing
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UHF-120 Ultra High Frequency Vibrometer
42
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Technical Specifications UHF-120
Ultra High Frequency Vibrometer
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Example: SAW Filter Measurement
Ultra High Frequency Vibrometer
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Example: SAW Filter 262 MHz
Ultra High Frequency Vibrometer
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•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
Conclusion