Fabrication and Evaluation of Electret Condenser Microphone using Poled Ferroelectric Ceramics

Abstract

PZT ceramics can emit a high electric field externally if surface charges are removed. For this study, the PZT surface charges were removed by heating. Then the electret microphones laminated with electrodes, insulation films, and a PZT element (disk) were prepared. Several contact conditions between laminated layers were examined to elucidate their influence on the microphones' sensitivity. The fabricated samples showed the same level of output (ΔVout) as a commercial electret microphone (sensitivity: 5.6 mV·Pa-1 [-45dB]), although the vibration amplitude of the fabricated samples was much smaller than that of the commercial microphone. The output measurement of laminating films under several conditions revealed that the interface gap between the layers had an important role in increasing the output. That of the fabricated samples, however, was degraded because of insufficient removal of surface charges and/or poor insulation properties. Furthermore, the output was temporarily decreased during heating between 50 and 180°C, but recovered after cooling to room temperature. Such behavior is explainable according to the pyroelectricity of PZT.