Capacitive silicon microphone

A capacitive silicon microphone has been fabricated. The component consists of two freestanding polysilicon membranes, a low-stress bending membrane a nd a high-stress backplate, which are separated by an air gap. Sound pressu re changes the capacitance between the membranes. A back-chamber is arrange d by encapsulation and static pressure changes are prevented with small equ alisation holes in the bending membrane. The: component is fabricated combi ning bulk and surface micromachining techniques. Silicon substrates are etc hed in TMAH and sacrificial oxide between the membranes is etched in PSG-et ch followed by freeze drying to prevent sticking. The measured acoustic sen sitivity of the microphone with 1 x 1 mm(2) membrane was 2mV/Pa (1 kHz freq uency) and the resolution 35 dB (A-weighted sound level).