Temperature characteristics of electret silicon microphones

The electret condenser microphone (ECM) has become an important component for various consumer equipment systems because of its stable sensitivity and frequency characteristics and its success in achieving small size and high sensitivity. A previous report described the method to design a microphone with stable temperature characteristics. The quality of the silicon material for the diaphragm was pointed out as important for improving robustness. Recently, microphones using micro-electro-mechanical systems (MEMS) have been practically applied and widely used for mobile equipment, such as cellular phones. The major reason for adopting MEMS is that a re-flow soldering process can be used in production, in addition to having desirable features such as being small and thin. However, almost no electret types have been commercialized since a guaranteed 300°C heat resistance is required. This report presents a new trial electret silicone microphone that contains a SiO2 thin-film electret. The report also evaluates the heat resistance of a SiO2 electret, the temperature stability of a silicon diaphragm, and the temperature change in sensitivity and frequency characteristics compared with those of a conventional ECM and the microphone for measurement.