Micromachined silicon subminiature microphones with piezoelectric P(VDF/TRFE)-layers and silicon-nitride-membranes

In this paper a silicon subminiature microphone is described, which is based on the piezoelectric effect of spin-coated P(VDF/TrFE)-layers. The polymer layers are placed on top of a very thin silicon nitride membrane, which is implanted with boron ions in order to reduce the tensile stress of the diaphragm, resulting in higher microphone sensitivities. A maximum sensitivity of 150 μV/Pa, a bandwidth of about 16 kHz and an equivalent noise level of less than 60 dB(A) were measured. Considering the small area of the membrane of the microphone (1 mm²), the sensors show a much better performance than former microphones with piezoelectric polymer layers