Microtech2010 2010

High Fidelit Loud Microspeaker Based on PZT Bimorph Diaphragm

Y. Choe, S.J. Chen, E.S. Kim
University of Southern California, US

Keywords: microspeaker, PZT, bimorph, diaphragm

Abstract:

This paper describes a microspeaker (composed of a 8mm square mechanically-polished PZT bimorph diaphragm and bulk-micromachined silicon top cover) that shows flat diaphragm displacement from DC to 11 kHz. A bimorph diaphragm is formed by gluing two 127µm thick PZT sheets and attaching them to a micromachined silicon substrate. With patterned electrodes on both sides of the diaphragm, the PZT bimorph can generate stresses with opposite signs along the thickness direction. The microspeaker with an encapsulating cylindrical package of about 0.7 cc inside volume produces sound pressure level (SPL) of 118 ~ 125 dB between 1 and 10 kHz when measured 5 mm away from the diaphragm with 190Vpeak-to-peak driving signal. The measured SPL drops as the frequency is reduced below 1 kHz, due to increasing wavelength and thus reduced total acoustic intensity over the measurement area. The diaphragm was indeed measured (with a laser vibrometer) to produce uniform displacement from DC to 11 kHz, as shown in Fig. 1. With 190Vpeak-to-peak sinusoidal input, the displacement at the center of the diaphragm was measured to have 7.25µm displacement at the fundamental resonant frequency of 11.3 kHz.
 
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