Index of content:
Volume 118, Issue 5, November 2005
- TRANSDUCTION 
118(2005); http://dx.doi.org/10.1121/1.2062429View Description Hide Description
Micromachined microphones with diffraction-based optical displacement detection are introduced. The approach enables interferometric displacement detection sensitivity in a system that can be optoelectronically integrated with a multichip module into volumes without beamsplitters, focusing optics, or critical alignment problems. Prototype devices fabricated using Sandia National Laboratories’ silicon based SwIFT-Lite™ process are presented and characterized in detail. Integrated electrostatic actuation capabilities of the microphone diaphragm are used to perform dynamic characterization in vacuum and air environments to study the acoustic impedances in an equivalent circuit model of the device. The characterization results are used to predict the thermal mechanical noise spectrum, which is in excellent agreement with measurements performed in an anechoic test chamber. An A weighted displacement noise of measured from individual prototype diaphragms demonstrates the potential for achieving precision measurement quality microphone performance from elements in size. The high sensitivity to size ratio coupled with the ability to fabricate elements with precisely matched properties on the same silicon chip may make the approach ideal for realizing high fidelity miniature microphone arrays (sub- aperture) employing recently developed signal processing algorithms for sound source separation and localization in the audio frequency range.