Double-chip condenser microphone for rigid backplate using DRIE and wafer bonding technology

Abstract: A novel silicon condenser microphone with a rigid backplate has been proposed and fabricated. The backplate is fabricated on a separated wafer from the membrane to enhance acoustic characteristics, and they are combined together by gold–tin (Au/Sn) eutectic solder bonding. On a 2.5mm×2.5mm, 0.5μm thick low stress silicon nitride membrane, 2mm×2mm Au/Ni/Cr membrane electrode is deposited including 3μm thick Au/Sn layer. A 2mm×2mm, 150μm thick single crystal silicon rigid backplate has 1.8mm×1.8mm backplate electrode, and an air gap, which is fabricated by bulk micromachining, and a silicon deep reactive ion etching. Slots and 50–60μm radius circular acoustic holes to reduce air damping are also formed in the backplate chip. The fabricated microphone sensitivity is 39.8μVPa−1 (−88dB re. 1VPa−1) at 1kHz using 28V polarization voltage. The microphone shows flat frequency response within 1dB from 20Hz at least up to 5kHz. [Copyright &y& Elsevier]