Design and Fabrication of Piezoelectric Acoustic Sensor

This paper describes a fully integrated acoustic sensor that combines high sensitivity, wide frequency range and low cost of batch processed miniaturized silicon components. A sputtered piezoelectric ZnO layer transforms the mechanical deflection of a thin-etched-Si diaphragm into a piezoelectric charge. ZnO has transparent and conductive properties, which makes it attractive for a variety of scientific and research applications such as surface acoustic wave filters, acoustic sensors, gas sensors, ultrasonic transducers and solar cells etc. ZnO is wide band gap semiconductor with energy of 3.37 eV & high excitation energy of 60 meV A 25-micron thin diaphragm Si is etched using wet chemical etching. This is followed by a deposition of sandwiched structure composed of bottom Al electrode, sputtered 3 micron of ZnO film and top Al electrode. A glass having 1um diameter hole was bonded on backside of the sensor to maintain sound pressure inside the cavity. Modeling and analysis of the acoustic sensor is performed using FEM technique, which describes the deflection of a generic m-layer piezoelectric multimorph sensor. Fabrication steps of the MEMS acoustic sensor are described Key-Words: MEMS sensors, acoustic sensors, piezoelectric sensors.