Performance and Modeling of a Fully Packaged Micromachined Optical Microphone

• Published in: Journal of microelectromechanical systems 2011-08, Vol.20 (4), p.828-833
• Main Authors: Kuntzman, M. L., Garcia, C. T., Onaran, A. G., Avenson, B., Kirk, Karen D., Hall, Neal A.
• Format: Article
• Language: English
• Subjects: Acoustic measurements; Acoustics; Audition; Biological and medical sciences; Diaphragms; Exact sciences and technology; Frequency response; Fundamental and applied biological sciences. Psychology; Fundamental areas of phenomenology (including applications); Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Interferometer; Mathematical models; Mechanical instruments, equipment and techniques; Microelectromechanical systems; microelectromechanical systems (MEMS); Micromechanical devices; Micromechanical devices and systems; Micromechanics; microphone; Microphones; Noise; Optical interferometry; Optical sensors; optical transducer; Packages; Perception; Physics; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Sensors; Transduction; acoustical devices for the generation and reproduction of sound
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2011.2148164

A microelectromechanical systems (MEMS) optical microphone that measures the interference of light resulting from its passage through a diffraction grating and reflection from a vibrating diaphragm is described ( JASA, v. 122, no. 4, 2007). In the present embodiment, both the diffractive optical element and the sensing diaphragm are micromachined on silicon. Additional system components include a semiconductor laser, photodiodes, and required readout electronics. Advantages of this optical detection technique have been demonstrated with both omnidirectional microphones and biologically inspired directional microphones. In efforts to commercialize this technology for hearing aids and other applications, a goal has been set to achieve a microphone contained in a small surface-mount package (occupying 2 × 2 mm × 1 mm volume), with ultralow noise (20 dBA) and a broad frequency response (20 Hz-20 kHz). Such a microphone would be consistent in size with the smallest MEMS microphones available today but would have noise performance characteristics of professional-audio microphones significantly larger in size and more expensive to produce. This paper will present several unique challenges in our effort to develop the first surface-mount packaged optical MEMS microphone. The package must accommodate both optical and acoustical design considerations. Dynamic models used for simulating frequency response and noise spectra of fully packaged microphones are presented and compared with measurements performed on prototypes.