Silicon-Micromachined Piezoelectric Bimorph Acoustic Transducer

Description The idea of using a bimorph structure for a micromachined piezoelectric acoustic transducer on parylene diaphragm has been invented and tested. Both the sensitivity and signal-to-noise ratio of the bimorph, parylene-diaphragm microphone have been demonstrated to be much higher than those of a conventional uni-morph piezoelectric microphone made on a silicon nitride diaphragm. Among various parylene materials, we find parylene-D to be the best choice for supporting the bimorph diaphragm because it can withstand high processing temperature and also is mechanically flexible. The micromachined piezoelectric bimorph microphone consists of two transverse-expander piezoelectric thin films secured together face to face in such a manner that mechanical bending of the element under acoustic pressure will cause it to develop a corresponding voltage between two outer electrodes. Since parylene-D has high thermal stability, it allows us to sputter-deposit (at 250 ºC) another ZnO layer on the backside of the wafer to form a face-to-face piezoelectric bimorph structure.

Applications Microphone, acoustic pressure sensor, microspeaker, acoustic transducers MEMS piezoelectric sensors and actuators (numerous arbitrarily shaped structures on silicon substrate) High performance and low cost parts in Audio system, communication system, multimedia system, hearing aid system High sensitive and biomedical compatible acoustic and ultrasonic transducers Main Advantages General advantages as a micromachined piezoelectric microphone Size miniaturization with extremely small weight Little power consumption and no polarization voltage needed Potentially low cost due to the batch processing and possibility of integrating microphones and circuits on a single chip Unique advantages of piezoelectric bimorph structure (Compared with a conventional uni-morph microphone) Easier control of the neutral plane position than a uni-morph structure and effective conversion of mechanical strain into electrical voltage and vice versa Simple structure containing only piezoelectric film, electrodes and very flexible parylene (does not introduce any significant stiffness in the diaphragm, nor residual stress); With larger sensitivity and signal/noise ratio and higher fundamental resonant frequency, it has inherently higher figure of merit than a uni-morph device. Conformal deposition allowing various diaphragm shapes

Type of Offer: Licensing

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