Packaging and Characterization of MEMS Optical Microphones

Abstract

Miniature microphones have numerous applications but often exhibit poor performance which can be attributed to the challenges associated with capacitive detection at small size scales. Optical detection methods are able to overcome some of these challenges although miniaturized integration of these optical systems has not yet been demonstrated. An optical interferometric detection scheme is presented and is implemented using micro-scale optoelectronic devices which are used primarily in fiber optic data transmission. Using basic diffraction theory, a model is developed and used to optimize the micro-optical system within a 1mm3 volume. Both omnidirectional and directional optical microphone designs are presented and a modular packaging architecture is assembled in order to test these devices. Results from the 2mm diameter omnidirectional optical microphone structure demonstrate a 26dBA noise floor. The biomimetic directional optical microphone, which has an equivalent port spacing of 1mm, demonstrates a noise floor of 34dBA. Additionally, these results demonstrate an array of two biomimetic directional optical microphones located on the same silicon chip and separated by less than 5mm. These results confirm the micro-optical detection method as an alternative to capacitive detection especially for miniaturized microphone applications and suggest that this method in its modular packaging architecture is competitive with industry leading measurement microphones.