Capacitive microphone with low-stress polysilicon membrane and high-stress polysilicon backplate

A capacitive single-chip silicon microphone with very low-stress polysilicon membrane was fabricated. A mechanism for stress-releasing due to the high stress of the perforated membrane was introduced. With the achieved stress level of 2 MPa, a microphone with the membrane area of 1 mm² can be optimally designed, although the measured components did not show the optimal resolution due to excessive acoustic resistance. With a membrane area of 1 mm², the acoustical sensitivity was 4 mV/Pa (at 1 kHz) and the noise equivalent sound level was 33.5 dB (A), which are adequate values for many applications. The packaged components were tested with a thermal cycle between -40 °C and +60 °C, and due to low packaging-related stresses, no buckling of the membranes was observed.