title: Towards a sub 15-dBA optical micromachined microphone.
abstract: Micromachined microphones with grating-based optical-interferometric readout have been demonstrated previously. These microphones are similar in construction to bottom-inlet capacitive microelectromechanical-system (MEMS) microphones, with the exception that optoelectronic emitters and detectors are placed inside the microphone's front or back cavity. A potential advantage of optical microphones in designing for low noise level is the use of highly-perforated microphone backplates to enable low-damping and low thermal-mechanical noise levels. This work presents an experimental study of a microphone diaphragm and backplate designed for optical readout and low thermal-mechanical noise. The backplate is 1 mm × 1 mm and is fabricated in a 2-μm-thick epitaxial silicon layer of a silicon-on-insulator wafer and contains a diffraction grating with 4-μm pitch etched at the center. The presented system has a measured thermal-mechanical noise level equal to 22.6 dBA. Through measurement of the electrostatic frequency response and measured noise spectra, a device model for the microphone system is verified. The model is in-turn used to identify design paths towards MEMS microphones with sub 15-dBA noise floors.
authors.affiliation: Microelectronics Research Center and Department of Electrical and Computer Engineering, The University of Texas at Austin, 10100 Burnet Road Building 160, Austin, Texas 78758.
authors.forename: Donghwan
authors.initials: D
authors.lastname: Kim
authors.affiliation: Microelectronics Research Center and Department of Electrical and Computer Engineering, The University of Texas at Austin, 10100 Burnet Road Building 160, Austin, Texas 78758.
authors.forename: Neal A
authors.initials: NA
authors.lastname: Hall
mesh_terms: D003198:Computer Simulation; D004867:Equipment Design; D007368:Interferometry; D008855:Microscopy, Electron, Scanning; D008962:Models, Theoretical; D009622:Noise; D061088:Photoacoustic Techniques / Q000295:instrumentation*; D017655:Silicon Compounds; D055672:Static Electricity; D014160:Transducers, Pressure
chemical_list: D017655:Silicon Compounds; C032734:silicon nitride