Design and Calculation of Micromachined Silicon Condenser Microphone with Free Floating Diaphragm and Gold Backplate

A micromachined condenser microphone with a free floating sensing diaphragm and a perforated thick gold backplate is presented. The diaphragm consists of a heavily doped layer of polycrystalline silicon and two layers of low stress silicon nitride. It is fabricated using low-pressure chemical vapor deposition (LPCVD). One end of rectangled sensing diaphragm sticks on silicon substrate while the other parts float from substrate, so that the intrinsic stress of diaphragm can be released. The gold backplate is fabricated using a photoresist-molded electroplating technology and perforated with circular vent holes. Perforated circular holes on backplate are laid out as hexagon to adjust air-gap damping between diaphragm and backplate to critical damping. Calculation and analysis show that the microphone has the open-circuit sensitivity of 13.78 mv/Pa at 5 V bias voltage reaches, the pull-in voltage of 31.85 V and the frequency bandwidth ranging from 0 to 142.3 KHz. All these performances of microphone can meet with the requirements of consumers.