Silicon Microphone

A microphone is a device that converts sound into an electrical signal. Broadcasting stations employ high-performance microphones that can pick up sounds ranging from faint to loud, without any sound distortion. However, the precision-made structure of conventional microphones constructed of plastic and metal parts makes them sensitive to heat, moisture, and physical shock. For this reason, we are working on a high-performance microphone that can be employed in any environment. In particular, our research involves a silicon microphone fabricated through semiconductor technology. The silicon microphones constructed in the past for broadcasting can be operated in severe environments with high temperatures, high humidity, acidity, etc., and via broadcasting, they have helped to open our ears to the diverse world of sound.

Silicon microphone structure

The central part of the silicon microphone (microphone element) consists of a thin diaphragm (2 µm to 3 µm thick), facing a backplate with a small gap between them (Figure 1). Movement of the diaphragm by sound pressure changes the capacitance between the diaphragm and the backplate. The operating voltage (42 V for broadcasting use) is applied between the backplate and diaphragm, and the output voltage changes as a result of the change in capacitance.

Characteristics and applications

The entire body of the microphone is formed from single crystalline silicon, which has an extremely high tensile strength; the device is durable and highly resistant to heat and moisture, and it has superior acoustic characteristics. It has proved to be a powerful tool that can operate under harsh conditions where conventional microphones could not be used at their full capacity. For instance, the microphone can pick up sound very close to a cooking pot (Figure 2) or sounds made by a hummingbird in flight in a hot, humid tropical rainforest.