Parylene Micromachined Piezoelectric Acoustic Transducers on Silicon Substrate
Description A new type of micromachined acoustic transducers, parylene micromachined piezoelectric acoustic transducers, has been developed and tested for use as microphones and microspeakers. The parylene diaphragms have about 100 times lower stiffness than silicon nitride, and considerably increase the sensitivity at audio range comparing with that of conventional device made by silicon nitride diaphragm. Also, the parylene diaphragm is almost free from the residual stress problem that considerably reduces the transducer sensitivity. Parylene micromachined piezoelectric acoustic transducers can be successfully fabricated with 1.5 µm thick flat or dome-shaped parylene diaphragms with electrodes and a piezoelectric ZnO film (5,000 µm2 flat square diaphragm and 2,000 µm in radius dome shaped diaphragm with a circular clamped boundary).
Parylene piezoelectric dome-shaped diaphragms have a number of advantages: the releasing of residual stress in the diaphragm through volumetric shrinkage or expansion produces a flexural vibration effectively from an in-plane strain (produced by a piezoelectric film sitting on a dome diaphragm), it also increases the figure of merit (the product of the fundamental resonant frequency squared and the DC response) based on the structural stiffness of dome. These advantages help the design to generate ultrasonic sound effectively.
Applications Computer Audio Industries Desktop dictation, videoconferencing, auto pc, headset speaker phone, directional array microphone Communication Industries Cellular Phone, Portable communication systems Hearing Aid Hearing aid, Directional hearing aid, Noise canceling, … Consumer Electronics Camcorder, Walkman, CD, MD, … Main Advantages Size miniaturization with extremely small weight Little power consumption Potentially low cost due to batch processing Excellent sensitivity as microphone and microspeaker High reliability, biocompatiblility Variety of structure Effectively releasing residual stress Effectively producing flexural vibration Large figure of merit (high amplitude and high frequency)
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