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 2.5 mm<TEX>${\times}$</TEX>2.5 mm, <TEX>$0.5{\mu}m$</TEX> thick low stress silicon nitride membrane, 2 mm<TEX>${\times}$</TEX>2 mm Au/Ni/Cr membrane electrode, and <TEX>$3{\mu}m$</TEX> thick Au/Sn layer. The backplate chip has 2 mm<TEX>${\times}$</TEX>2 mm, <TEX>$150{\mu}m$</TEX> thick single crystal silicon rigid backplate, 1.8 mm<TEX>${\times}$</TEX>1.8 mm backplate electrode, and air gap, which is fabricated by bulk micromachining and silicon deep reactive ion etching. Slots and <TEX>$50-60{\mu}m$</TEX> radius circular acoustic holes to reduce air damping are also formed in the backplate chip. The fabricated microphone sensitivity is <TEX>$39.8{\mu}V/Pa$</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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