Fabrication and Annealing Temperature Optimization for a Piezoelectric ZnO Based MEMS Acoustic Sensor

Abstract

This paper reports the development of an acoustic sensor structure with a square-shaped diaphragm with side length 1750 μm. The fabricated structure has been annealed at different temperatures and is characterized using a laser Doppler vibrometer (LDV). The piezoelectric zinc oxide (ZnO) layer is deposited using radio frequency sputtering technique. Post thermal annealing of the deposited film is done at different temperatures and characterized using x-ray diffraction (XRD). The investigations show maximum piezoelectricity of the annealed ZnO film at 400°C. This optimized sample annealed at 400°C is also characterized using atomic force microscopy and field emission scanning electron microscopy. The results showed a smooth and crack-free surface morphology. The experimental resonant frequency of fabricated devices also tested using LDV and its velocity response at the same applied voltage of 2 V followed a similar trend as in XRD results. This annealing temperature optimization plays an important role to determine the fabrication process parameters and generation of voltage corresponding to applied pressure on an acoustic sensor.