Study on deformation of a microphone membrane using multiple-wavelength interferometry

Abstract

Determination of deformation of a microphone membrane under electrical loads (varying voltage) is of fundamental importance for the design and fabrication of a microphone. This paper reports a technique for measuring the deformation of a thin membrane (2 μm) in a silicon-based condenser microphone. A typical condenser microphone consists of two parts: a compliant membrane and a perforated rigid backplate. Interference patterns under various interference filters with wavelengths of 700, 589 and 532 nm are recorded through a microscope by a CCD sensor. A simple algorithm for recording both integral and fractional fringes using different wavelengths is presented. From the fringe pattern deformation of the membrane in the sub-micron range is obtained. The proposed method enhances the lateral resolution and improves measurement accuracy. © 2001 Elsevier Science B.V. All rights reserved.