Thick-mode resonance of a PZT/Si wafer stack investigated by X-ray diffraction in Bragg geometry

X-ray diffraction in Bragg geometry was used to investigate the effects of standing longitudinal acoustic waves on an Si(111) wafer. A PZT/Si(111) stack with a resonant frequency of 2.34 MHz was constructed. In addition to the ultrasonic vibration, a thermal effect is evident. The thermal contribution causes an angular displacement of the Bragg profile and was mapped without time resolution. The actual ultrasonic oscillation of the surface was measured using a stroboscopic system. Bulging of the Si(111) surface was mapped out and the maximum deformation near the centre of the Si wafer was determined for a given ultrasonic power. Simple modelling using finite differences was helpful in determining the acoustic and thermal contributions.