Deposition and process development of AlN for MEMS acoustic sensor

This paper describes a technique for fabrication of AlN based structure for MEMS acoustic sensor and similar applications. The AlN films of 2.1 μm thickness are grown on silicon substrates by reactive sputtering. The deposited films are characterized to determine the crystalline quality and piezoelectricity. Thermal annealing of the deposited films are performed at different temperatures for better piezoelectricity. The investigation showed a c-axis oriented AlN film is obtained at 600 °C temperature. A simple AlN based structure for MEMS acoustic sensor is fabricated on a thin silicon diaphragm. During fabrication of structure, a wet etching technique of AlN was developed. The reliability testing of fabricated structured was performed. The maximum current that can be passed across Al-deposited AlN edge was found to be 3.05 A without any damage. The investigations show a uniform Al step coverage on a 2.1 μm-thick AlN edge using proposed technique. The proposed technique for AlN etching reduces the process complexity and providing better reliability of fabricated structure. The resonance frequency of fabricated AlN based structure was measured and found to be 42.9 kHz.