Non-Contact Vibration Measurement of Micro-Structures

Transcription

1 Non-Contact Vibration Measurement of Micro-Structures Using Laser Doppler Vibrometry (LDV) and Planar Motion Analysis (PMA) to examine and assess the vibration characteristics of micro- and macro-structures. Including MEMS, MOEMS, SPM's, sensors, bio-structures, computer and other electronic devices, etc. Roger Traynor, Laser Vibrometer Specialist at Lambda Photometrics, the UK division of Polytec

2 Non-Contact Vibration Measurement of Micro-Structures In addition to measuring the surface finish and flatness of Micro-Structures, there is also an increasing need to assess their motion and vibration characteristics Some devices (e.g. actuators, switches, etc) are designed to move in a defined way and need to be checked. Others can be prone to operational malfunction or even failure if vibration is not taken into account Non-contact Laser Doppler Vibrometry (LDV) and Planar Motion Analysis (PMA) are complimentary tools that enable the design or test engineer to carry out this characterisation

3 The Basics: What is Laser Doppler Vibrometry? A Laser Doppler Vibrometer is a type of optical interferometer that measures velocity, as opposed to displacement, which is the norm for other interferometers (e.g. the Zygo NewView, shown below) Zygo NewView 5000 The Zygo uses Michelson or Mireau optics to map the surface profile and/or shape to show flatness, surface roughness, etc.

4 The Basics: Laser Doppler Vibrometer Operation Randomly Polarised Laser Polarising Beamsplitter P/B Waveplate Circularly Polarised Light (to target) Bragg Cell Modulator Detectors CPL (from target) + - Output Vibrometer Controller Time History Impulse Response Frequency Response

5 Advantages of Laser Vibrometry: Non-Contact Zero mass-loading Quick, easy to set-up Eye-safe, low power visible laser (Class II) Wide frequency range: near DC to 30 MHz Velocities from >0.5µm to ±30m/s Displacements from sub nm to >±41mm

6 Scanning a Laser Vibrometer By the addition of scanning mirror mechanics, a single point vibrometer can be converted to quickly and easily map large, macro or micro-structures (e.g. from buildings to SPM tips)

7 Micro-Scanning a Laser Vibrometer Basic Configuration of a Microscope Scanning Vibrometer The MSV-300 comprises an optical fibre interferometer model coupled into a standard microscope via a piezo-electrical scan unit. Vibration information from the interferometer is processed by the OFV vibrometer controller. A Windows workstation is responsible for scan point definition, data acquisition and control of the entire system. Vibrometer Sensor OFV-511 Vibrometer Controller OFV-3001 Scan Electronics Data Management System with NT Workstation Test object

8 Vibration Scanning of Structures-What is the Performance? Polytec PSV-300 Series Scanning Laser Vibrometer: ± 20 scan field or down to ~1mm x 1mm square area using add-on close up attachment laser spot size to ~4 µm diameter Polytec MSV-300 Micro-Scanning Laser Vibrometer: ~ 3.5mm square, down to ~70µm square areas, dependent on microscope objective used (x2 to x100) laser spot size to ~1 µm diameter Both Systems: near DC to 30 MHz frequency capability ± 10 m/s velocity range (< 0.3 µm/s resolution) sub-nm displacement resolution comprehensive integrated control, acquisition, display & analysis software

9 Vibration Measurement of Structures-What Can You Measure? Macro (by direct viewing) :- Computer, electronic plus telecomms components and sub-assemblies Mobile phone & hearing aid assemblies and components Miniature Motors, sensors & piezo devices Bio-structures, medical/hearing applications Others Micro (via a microscope) :- Micro-Electric and Micro-Optical Mechanical Structures (MEMS, MOEMS) Gyroscopes Micro-motors Sensors Micro-switches Scanning Probe measurement devices (STM, SOM, AFM cantilevers Others

10 Polytec Macro-Scanning Vibrometer Measurements-Examples Computer HDD read/write head & suspension unit Animated 3D wiregrid Measured points Animated 2D colour map

11 Polytec Macro-Scanning Vibrometer Measurements-Examples SEM image of a Pressure Sensor (courtesy of Newcastle University) Surface profile map (Zygo NewView) Scan showing vibration distribution over the measured area (top) and resonant frequency response (bottom)

12 Polytec Macro-Scanning Vibrometer Measurements-Examples Pressure Sensor vibration characteristics at: khz khz khz khz

13 Polytec Micro-Scanning Vibrometer Measurements-Examples Similar mirror, for optical switching/steering (resonant frequency 575 Hz) Micro-resonant mirror showing motion around a gimbal pivot

14 Polytec Micro-Scanning Vibrometer Measurements-Examples Automotive Airbag Sensor Effectively a mechanical vibration spectrum analyser that detects impact Impacts of different ferocity and/or direction cause a combination of sensor fingers to respond and fire the vehicle s appropriate airbag(s) Frequency Response (primarily resonant in the khz region)

15 Macro/Micro-Scanning Laser Vibrometers - More Examples Travelling wave motors... Bio - for hearing performance testing and corrective devices Even Fly Hearing!

16 Non-Contact Vibration Measurement of Micro-Structures All the previous measurements were taken in the Out-of-Plane direction, i.e. up and down the line of sight of the laser, But many MEMS actuators have motion in the lateral direction. For these measurements other techniques are needed Polytec s solution is a Video Microscopy technique called: Planar Motion Analysis

17 Polytec MMA-300, with combined MSV and PMA Technologies OFV 074 OFV 077 LED Camera OFV 076 Video Signal Vibrometer Microscope Specimen Lamp MEMS driver LED driver Signal generator

18 Polytec MMA-300 Specifications: Out-of-Plane (Vibrometry) Frequency range: ~0-1.5 MHz Maximum velocity: 10 m/s Resolution: 1 pm (depending on frequency) Max. motion amplitude: depth of focus Synchronization with motion is not necessary In-Plane (Videomicroscopy) Frequency range: ~0-1 MHz Maximum velocity: 10 m/s Resolution: < 2nm (depending on magnification) Max. motion amplitude: field of view Synchronization with motion is necessary

19 time PMA Method of Operation Camera Exposure 1 driving signal LED flashes camera exposure

20 time PMA Method of Operation Camera Exposure 2 driving signal LED flashes camera exposure

21 time PMA Method of Operation Camera Exposure 3 driving signal LED flashes camera exposure

22 time PMA Method of Operation Camera Exposure 4 driving signal LED flashes camera exposure

23 PMA User Interface and a typical measurement result Laterally Vibrating Comb at 5800 Hz

24 Advantages of MMA: A hybrid system that exploits the advantages of 2 measurement principles (Vibrometry and Stroboscopic Video Microscopy) Rapid evaluation of resonance frequencies by fast broad band excitation (using Laser Doppler Vibrometry) In-situ evaluation of the in-plane behaviour by using the results of out-of-plane measurement. Short measurement time Can evaluate non-linear systems Can evaluate non-periodic motions

25 Summary: Polytec s MMA-300 system provides a new tool for microdevice development and test engineers to simultaneously measure all three axes of vibration Measurements are made at the same time, preserving phase-related conditions In-plane vibration is examined and evaluated via video microscopy, in both live and acquisition modes. Out-of-plane vibration is measured by the well established and proven Scanning Doppler Laser Vibrometry technique MMA can provide the fastest evaluation of MEMS devices general behaviour, using broad band excitation

26 Acknowledgements: I would like to thank the DMAC and NPL for inviting me to talk about Polytec and Lambda Photometrics work in the field of Micro-Structure measurement. I would also like to thank my colleagues in Polytec worldwide, who have helped tackle the difficult micro-structures measurement problems, and for provided the tools to solve them. AND THANK YOU FOR LISTENING Roger Traynor, Vibrometry Product Group Manager Lambda Photometrics Ltd, Lambda House, Batford Mill Industrial Estate, Harpenden, Herts, AL5 1SR, UK Tel: Fax: roger@lambdaphoto.co.uk Website: