A NOVEL INTEGRATED SILICON CAPACITIVE MICROPHONE - FLOATING ELECTRODEELECTRET MICROPHONE (FEEM)

A novel principle ''electret'' microphone, i.e., floating electrode el ectret microphone, is proposed and implemented in this study. Single-c hip fabrication and corrugation technique are used in the design and f abrication of the microphone. The floating electrode is encapsulated b y highly insulated materials to ensure that there is no electric-leaka ge passage between the floating electrode and the electrodes of the mi crophone. Net-free electronic charges (not ''bonded'' charges as in tr aditional electret) in the floating electrode can excite the electric field, which is similar to that of the traditional electret, The float ing electrode can be easily charged by use of the ''hot'' electron tec hnique, available using the avalanche breakdown of the p(+)-n junction . Therefore, the electret microphone is rechargeable, which can greatl y increase the lifetime of the device. The preamplifier has been on-ch ip integrated in a junction-held-effect transistor (JFET) source-follo wer type with resistors by use of ion implantation. Electret charges a re bonded in a deep potential trap, thus, this microphone can operate at a high temperature las high as 300 degrees C) and has high stabilit y and reliability. Experiments show that the prototype has a 3-mV/Pa s ensitivity and a larger than 21-kHz frequency bandwidth in a 1 mm x 1- mm diaphragm area. Microphone performance can be further improved by o ptimized process and design. The fabrication is completely integrated- circuit (IC) compatible, hence, the microphone shows promise in integr ated acoustic systems.