STRESS DETERMINATION OF MICROMEMBRANES USING LASER VIBROMETRY

A laser vibrometry based dynamic technique for biaxial residual stress determination in micromembranes is reported. Layered, low pressure ch emical vapor deposition grown, rectangular shaped micromembranes are u ltrasonically excited. The resulting micromembrane displacement, as a function of frequency and position, is recorded to yield resonance fre quencies and associated vibrational mode numbers. The stress is determ ined from this information. Vibrations forced from ultrasonic pressure (similar to 25 Pa) resulted in peak displacements of tens of nanomete rs at resonance. For the sample set studied, the (3,1) mode resonance peak displayed the least damping in atmospheric testing and was used t o establish stress levels similar to 10(8) N/m(2). A trend for this st ress showing an overall decrease by similar to 40% as a result of ther momechanical cycling was identified. (C) 1996 American Institute of Ph ysics.