Silicon subminiature microphones with organic piezoelectric layers-fabrication and acoustical behavior

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Abstract
A silicon subminiature microphone, based on the piezoelectric effect of organic films such as aromatic polyurea, PVDF, and PVDF/TrFE, is proposed. The acoustical sensor is fabricated using a slightly modified integrated circuit technology process and a standard micromechanical fabrication procedure. The main production steps of this hybrid sensor are given, including the fabrication of the mechanical part of the sensor, the deposition or spin coating of the films, and the poling of the polymer layers. Measurements of the transverse piezoelectric charge constant d/sub 31/ yield values up to <or=20 pC/N for the PVDF films. Furthermore, the acoustical behavior was determined. The maximum measured sensitivity to airborne sound of the aromatic polyurea microphones is approximately 126 mu V/Pa, whereas typical sensitivities are between 4 and 30 mu V/Pa.