Design and fabrication of an integrated programmable floating-gate microphone

An integrated, programmable floating-gate capacitive microphone has been designed and fabricated. The conducting floating-gate is electrically insulated and is "programmed" by injecting electrons into it using Fowler-Nordheim tunneling through a thin silicon dioxide film, thus capable of simulating an electret and generating a permanent electric field. A current-driving buffer based on metal-oxide-semiconductor field-effect transistors is integrated to reduce the capacitive loading of the microphone. The fabrication process is MOS compatible and promises the potential of integrating a variety of signal processing electronic circuits.