Abstract

This paper describes our first demonstration of the parylene-diaphragm piezoelectric acoustic transducer as a fully functional microspeaker and also characterization of its vibration amplitude and sound pressure output. The piezoelectric microspeaker is built on a 1.5 μm thick parylene diaphragm (5,000*5000 μm2 square diaphragm micromachined in a silicon substrate) with electrodes and piezoelectric ZnO film. The parylene (a polymer material) has very low elastic modulus (about 50 to 100 times smaller than conventional diaphragm materials such as silicon nitride, stainless steel, etc), and is an outstanding material for a speaker application. The speaker is shown to produce a maximum sound-pressure level of 91 dB SPL into 2 cm3 acoustic coupler at a resonant frequency of 9.5 kHz. The vibration amplitude at that frequency is measured to be 1.8 μm with a laser doppler meter. Proper packaging of the microspeaker improves the sound output by preventing the cancellation of the sound output from the backside that has 180 degree out of phase.

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