Progress in silicon microphones

Recently, several advances have been made in the design, technology, and performance of silicon microphones. New or significantly modified transducers are: (1) condenser microphones consisting of a single chip processed with sacrificial‐layer technology to form the electrode‐air gap system; (2) condenser microphones with small parasitic capacitance to decrease the load on the sensor output; (3) optical‐waveguide microphones utilizing novel waveguide designs and operating with intensity modulation, which, to date, has not been used in acoustic silicon sensors. Also, attention has been given to various types of ultrasonic silicon microphones for airborne sound. Of importance in all implementations is the equivalent noise level, which is, in some microphone‐preamplifier systems, sufficiently low for certain applications, but still higher than for conventional microphones. The present state of the art with respect to transducer design and performance will be discussed.