A surface micromachined MEMS capacitive microphone with back-plate supporting pillars

Abstract

We present a new surface micromachined MEMS capacitive microphone with improved frequency response and high sensitivity. The proposed MEMS microphone has a top back-plate with a bottom sensing membrane and the back-plate is supported by supporting pillars which are anchored to the bottom of the deep back chamber. The back-plate supporting pillars increase the stiffness of the back-plate and prevent deformation. A present surface micromachined MEMS capacitive microphone is fabricated using fully CMOS compatible processes. It has a thin metal membrane of 500 μm diameter, a sensing air gap of 2.5 μm and seven back-plate supporting pillars. A 100 μm deep back chamber is formed by xenon difluoride dry etching of silicon substrate. As a result, the proposed microphone shows a flat frequency response and high open-circuit sensitivity. It shows a measured zero-bias capacitance of 1.0 pF and a pull-in voltage of 11.0 V, and an open-circuit sensitivity of 10.37 mV/Pa on a DC bias of 6.0 V.