Carrier lifetime influence on clamped silicon wafer resonance by PTA effect

Laboratoire IES, UMR CNRS 5214, Université de Montpellier 2, Place Eugène Bataillon, 34095 Montpellier, France

Corresponding author: carine.chapus@ies.univ-montp2.fr

Received: 23 October 2009
Revised: 25 February 2010
Accepted: 12 March 2010
Published online: 16 April 2010

Abstract

This experimental work presents reproducible measurement conditions to allow amplification of the mechanical vibration generated by photo-thermo-acoustics (PTA) effect using the resonance of circular silicon membranes clamped by nitrile o-rings on a diameter of 30 mm (D_i). We use wafers with various thickness (h) between 250 and 1000 μm and with carrier lifetime between 3 and 30 μs. Under the condition to have a resolution of few picometers for the measurement, it is possible to characterize the resonance mechanism obtained without contact by conventional laser vibrometry using a modulated laser diode of only a few milliwatts of power. Compared to perfect clamped membranes, the first Eigen frequency presents a downward shift of some hundreds Hertz due to the circular clamping by o-ring as predicted by our simplified model. The resonance frequency depends linearly on the thickness as long as D_i/h > 80. The quality factor (Q) does not exceed ten in agreement with our model for spring loaded membrane in air. The low value of quality factor and its variation according to thickness follow our predictions. Moreover, Q is independent of carrier lifetime whereas first resonance amplitude increases with it but less than prediction for bulks.