Micromachined piezoelectric polymer membrane acoustic sensor

This paper reports on a 2.3 mm x 2.3 mm polymer micro-electromechanical systems (MEMS) for air transducer applications. The MEMS, used as a receiver of ultrasonic signal, has a suspended membrane structure. A 2.7 mu m thick poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] 70/30 mol% copolymer was spun on a silicon dioxide/silicon substrate and then poled in-situ. The Si substrate was then etched from the backside by anisotropic chemical etching in KOH to produce a P(VDF-TrFE)/SiO 2 /Si suspended membrane structure. The displacement of the membrane was measured by means of a laser vibrometer. The maximum deflection at the center of the membrane was 0.9 mu m at 40.8 kHz under an input drive of 7 V. A commercial air transducer was used as the transmitter to emit ultrasound at 40.8 kHz. The MEMS acoustic transducer, which has similar resonance frequency, was used as the receiver. The temporal response of the MEMS and its sensitivity were measured. The result suggested that the MEMS has potential for monitoring ultrasound emission.