Micromachined Microphones with Diffraction-based Optical Interferometric Readout and Electrostatic Actuation
نویسندگان
چکیده
Micromachined microphones that use a diffraction-based optical method for integrated interferometric detection of diaphragm displacement are described. With optoelectronics integration, this approach yields highly sensitive microphones in mm-cube volumes. Furthermore, the electrical port of the device, which is freed by optical detection, is used for electrostatic actuation of the microphone diaphragm to adjust microphone characteristics via force feedback and to generate self characterization signals. This approach also changes the paradigm for the backplate and gap structure design enabling use of millimeter size diaphragms to achieve wide frequency response and low thermal mechanical noise levels characteristic of precision measurement microphones. Prototype optical microphone structures with polysilicon diaphragms have been fabricated using Sandia National Laboratories' silicon based SwIFTLite(TM) process. Measurements on these diaphragms show an A-weighted diaphragm displacement noise of 2.4-pm and flat electrostatic response up to 20-kHz. Straightforward design improvements lead to measurement microphones with 1.5-mm diameter diaphragms, 15-dBA internal noise, and 20-kHz bandwidth. Application of the detection method in a bioinspired directional microphone for hearing aids, and packaging development for half-inch calibration microphones are also discussed.
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