Abstract
This paper presents a novel MEMS condenser microphone with rigid backplate to enhance acoustic characteristics. The MEMS condenser microphone consists of membrane and backplate chips which are bonded together by gold-tin(Au/Sn) eutectic solder bonding. The membrane chip has <TEX>$2.5mm{\times}2.5mm$</TEX>, 0.5<TEX>${\mu}m$</TEX> thick low stress silicon nitride membrane, <TEX>$2mm{\times}2mm$</TEX> Au/Ni/Cr membrane electrode, and 3<TEX>${\mu}m$</TEX> thick Au/Sn layer. The backplate chip has <TEX>$2mm{\times}2mm$</TEX>, 150<TEX>${\mu}m$</TEX> thick single crystal silicon rigid backplate, <TEX>$1.8mm{\times}1.8mm$</TEX> backplate electrode, and air gap, which is fabricated by bulk micromachining and silicon deep reactive ion etching. Slots and <TEX>$50{\sim}60{\mu}m$</TEX> radius circular acoustic holes to reduce air damping are also formed in the backplate chip. The fabricated microphone sensitivity is 39.8 <TEX>${\mu}V/Pa$</TEX>(-88 dB re. 1 V/Pa) at 1 kHz and 28 V polarization voltage. The microphone shows flat frequency response within 1 dB between 20 Hz and 5 kHz.
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