High sensitivity acoustic transducers with thin p+ membranes and gold back-plate

High sensitivity acoustic transducers (microphones) have been fabricated on 5″ wafers in a production environment and the experimental results are presented. One of the main advantage of this microphone design is that it can be fabricated on a single wafer eliminating the need for the multiple wafers and subsequent wafers bonding steps as in conventional designs. The devices use thin (approximately 3 μm) p+silicon membranes as the active movable element and a thick perforated plated gold back plate. The p+membranes are fabricated using an optimized boron solid source diffusion at 1150 °C. Ethylene-Diamine-Pyro-Catecol (EDP) etching at 100 °C was performed from the backside of double-sided polished wafers to release the thin silicon membranes. The zero-bias capacitance with the air gap was 2.2 pF and it increased to 2.4 pF at 9 V. The frequency response was measured and the measured sensitivity of 5.28 mV/Pa at 5 V and 10.77 mV/Pa at 9 V at 1 kHz are among the highest reported in literature for micro-machined acoustic transducers.