Jonathan J. Bernstein
The Charles Stark Draper Lab., MS 37, 555 Technology Square, Cambridge, MA 02139
Draper Laboratory has fabricated and tested several generations of micromachined silicon microphones. These monolithic microphones include on-chip JFET buffer amplifiers, providing a complete microphone plus electronics on a single silicon chip. Recent test data will be presented showing sensitivities as high as 40 mV/Pa (-48 dB re: 1 V/(mu)Bar), with routine sensitivity of 15 mV/Pa (-57 dB re: 1 V/(mu)Bar) and bandwidth of 70 Hz to 20 kHz. The particular constraints resulting from use as a hearing aid microphone are the available bias voltage (one volt at end of battery life) and the small package volume. An analysis of the theoretical attainable sensitivity of a micromachined microphone will be presented. This analysis shows that useful sensitivities (15 mV/Pa) can be attained with a 1-V bias in a small (15 mm[sup 3]) internal package volume. [Work supported by Noise Cancellation Technologies, Inc.]