Improving Performance of Mems Using Dynamic Characterizaton


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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.

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Improving Performance of Mems Using Dynamic Characterizaton

  1. 1. Improving Performance of MEMS Designs Using Dynamic CharacterizationAdvancing Measurements by Light • 1
  2. 2. Polytec IntroductionEric LawrenceMEMS Business DevelopmentManagerAdvancing Measurements by Light • 2
  3. 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. 4. Optical Measurement SolutionsLaser Doppler VibrometersFor non-contact vibrationmeasurementsLaser Surface VelocimetersFor surface speed and lengthmeasurementsWhite Light InterferometersFor surface topographymeasurementsAdvancing Measurements by Light •
  5. 5. Tools for Vibration AnalysisPolytec Scanning VibrometerData Storage Fast, accurate visualization and analysis of structural vibration MEMS Automotive Health Monitoring Aerospace Micro Electro Mechanical Structures (MEMS)
  6. 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. 7. MotivationWhy 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. 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. 9. Laser Doppler Vibrometry Signal Demodulation FM Doppler signal ControllerPhoto-detector system Voltage ~ Velocity AM electrical signal FFT Spectrum Voltage ~ Displacement
  10. 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. 11. Scanning Laser Doppler Vibrometer Vibration Time Signal sequential measurement at all points. Excitation for all points Vibration Spectrum
  12. 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 testingAdvancing Measurements by Light •
  13. 13. In-plane: Strobe Video MicroscopyAdditional Strobe Video MicroscopyCapability for in-plane motionIn-Plane motion of MEMS Comb drives Gyroscopes AccelerometersAutomatically acquires strobe image setsPattern Matching to measure displacementSoftware tools for analyzing response
  14. 14. Topography: White Light InterferometryAdditional Topography Measurement CapabilityTopographical Measurement of: Step-Height Shape (Curvature, Flatness) Roughness Form Parameters (Dimensions, Angle, Radius)
  15. 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. 16. ApplicationsAdvancing Measurements by Light •
  17. 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. 18. Example: Comb Drive ResonatorSetup: 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. 19. Example: Comb Drive ResonatorFrequency 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. 20. Example: Comb Drive Resonator 1610 KHz13.8 KHz Operational Deflection shapes Resonance 526 KHz displayed for each frequency peaks frequency graphical selected by corresponds to a interface tool unique mode
  21. 21. Example: Comb Drive Resonator Fundamental rigid body resonance at 13.8 KHz
  22. 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. 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. 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. 25. Example: Texas Instruments mdisplayHinge 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. 26. Example: Texas Instruments mdisplayHinge 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. 27. Example: Texas Instruments mdisplayHingeAxis • 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. 28. Example: Texas Instruments mdisplay• The base motion directions above are shown for a singlemirror. Ability is implemented to acquire and process data onseveral mirrors to provide dynamics where we can compareresults mirror-to-mirror… 28
  29. 29. Example: Texas Instruments mdisplay• Image above (left)shows one of theprocessing/visualizationwindows withinMatLab.• In this case, a (3x3)array of mirrors areshown with theircorresponding tilt, rolland sag axis timedeveloped dynamics inthe right side of figure. 29
  30. 30. Example: CantileverModel for Modal Response of Cantilever based onmechancial 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. 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 InstrumentePart # 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:
  32. 32. Example: CantileverFrequency 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. 33. Example: Cantilever1st Bending Mode: Discrepancy: -29%Experimental Data: Model:
  34. 34. Example: Cantilever2nd Bending Mode: Discrepancy: -23%Experimental Data: Model:
  35. 35. Example: CantileverTorsion Mode: Discrepancy: -49%Experimental Data: Model:
  36. 36. Example: Cantilever ArrayMeasurement on poly3 400 umcantilever showing resonance at18.45 KHz and damping factor0.10 (squeeze film damping)
  37. 37. Example: Wafer level testingPARTEST: Testing Methods for Determination of Production RelevantParametersin MEMS on Wafer Level
  38. 38. Example: Wafer level testingElectrostatic 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. 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. 40. Example: Wafer level testing
  41. 41. Example: Wafer level testing mean( EIE) = 0.08µm std( EIE) = 0.04µm 0.25Wafer map withClassification 0.2 EIE [µm] 0.15 0.1 0.05 Peak error max. EIERed spots show bad dies EIE: Estimated Identification Error
  42. 42. UHF-120 Ultra High Frequency Vibrometer 42
  43. 43. Ultra High Frequency VibrometerTechnical Specifications UHF-120
  44. 44. Ultra High Frequency VibrometerExample: SAW Filter Measurement
  45. 45. Ultra High Frequency VibrometerExample: SAW Filter 262 MHz
  46. 46. Conclusion• Polytec MSA unique, all-in-one opticalmeasurement solution for 3D vibrationmeasurement plus topographymeasurement• Real-time, broadband measurementwith frequency response in milliseconds• Highly Sensitive measurement withresolution down to picometer level• Well supported by engineersknowledgeable with MEMS applicationsand necessary requirements for testing Advancing Measurements by Light •