High sensitivity acoustic transducers with thin p plus 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(similar to 3 mu m) 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 degrees C. Ethylene-Diamine-Pyro-Catecol (EDP) etching at 100 degrees 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. (C) 1999 Elsevier Science S.A. All rights reserved.