MEMS characterization using new hybrid laser Doppler vibrometer/strobe video system

Abstract

Laser Doppler Vibrometry (LDV) is a widely accepted tool for dynamic characterization of MEMS. Using automated scan capability, the Polytec system can measure structural resonance and display out-of-plane deflection shapes with amplitudes down to the picometer level and frequencies to 30 MHz. By adding stroboscopic video microscopy for in-plane motion analysis, our combined Micro Motion Analysis (MMA) system is capable of threedimensional dynamic characterization. The MMA system opens up new possibilities to measure in-plane actuators previously difficult or impossible for LDV measurements. To exemplify the use of this technology, we present characterization measurements on MEMS devices fabricated by Sandia National Labs SUMMiT V process. Multiaxis measurements reveal the complex motions exhibited by an electrostatic comb drive driven at resonance. Also, ultra-high resolution velocity measurements are made on passive cantilever structures oscillating under thermal excitation. Picometer resolution makes possible detection of these purely mechanical resonances. Both comb drive and cantilever data are used to determine mechanical properties important to evaluate the reliability of fabrication processes. This study demonstrates the unique performance of our hybrid LDV / strobe video measurement system for quick, accurate, high-resolution dynamic response measurements.

A new non-contact automatic inspection method for micro-structures

“…mechanical properties) and defects of the devices. Lawrence and Rembe [8] used this method to characterize electric comb drives and Laser doppler vibrometry has the significant drawback that is not an entirely non-intrusive inspection technique. At the micro-scale, thermal loading may in fact alter the mechanical properties of the devices, or even severely damage the micro-structures [10].…”

“…mechanical properties) and defects of the devices. Lawrence and Rembe [8] used this method to characterize electric comb drives and Fig. 3 Block diagram of proposed system cantilevers, and Michael et al [9] used it to inspect membrane structures of micro-electro-mechanical systems.…”

Testing and Standards for Qualification

“…For instance the Polytec MSA-500 combines scanning laser Doppler vibrometry, White light interferometry, and strobed in-plane vision recognition. This system provides in-plane motion analysis by adding a stroboscopic video system to the LDV that synchronizes LED flash time and camera on-time to the excitation of the MEMS structure [13].…”

Multi-technique platform for dynamic and static MEMS characterisation

“…Moiré methods enable full-field measurements without scanning [5]. The detection of the resonance frequency is another important task enabled by laser Doppler vibrometry [6].…”