Novel in-plane gap closing CMOS-MEMS microphone with no back-plate

The stacking of metal/tungsten layers as the sensing electrodes for CMOS-MEMS microphone without the back-plate has been proposed and demonstrated for the first time. The acoustic pressure will deform the spring-diaphragm structure and further cause the in-plane gap-closing between sensing electrodes. Thus, acoustic pressure and dynamic response of spring-suspension can be determined by the sensing capacitance changes. Such design has the following merits: (1) no back-plate is required, (2) bias voltage to pull diaphragm close to back-plate is not required, (3) in-use pull-in and process stiction between diaphragm and back-plate is also prevented, (4) easy integration with sensing circuits. The design was implemented using the standard TSMC CMOS process. Typical microphone with 200μm-diameter diaphragm and 48-pairs sensing electrodes has been realized. Measurements show the sensitivity of microphone is -64.78dBV/Pa at 1kHz.