Piezoelectric thin film ZnO on Si integrated microphone

Abstract

Recent technology advances in thin film deposition and in fabrication of Si microstructures have made possible the development of a new class of “intelligent” sensors having electronics and sensing element integrated on the same Si chip. The present paper describes a fully integrated microphone which combines high sensitivity, wide frequency range, low power, and low cost of batch processed miniature silicon components. A thin piezoelectric layer of ZnO transforms the mechanical deflection of a thin Si diaphragm into a piezoelectric output voltage. This signal is directly connected to an amplifier built on the same chip. A unique annular electrode design provides cancellation of temperature induced parasitic signal due to the pyroelectric effect in ZnO. Integrated devices were fabricated and tested. Measured performances were: sensitivity of 25 μV/μbar, a signal to noise ratio of 5:1 at 2 μbars, a frequency response of 0.1 Hz to 10 kHz and a power consumption below 40 μW. Further improvements in the onchip electronics should increase the signal to noise ratio by an order of magnitude bringing its value in the range of the conventional hearing aid devices.