Design and Fabrication of Silicon Nanowire-based MEMS Microphones

This paper presents a design and fabrication process flow of silicon nanowire (SiNW)-based micro-electro- mechanical system (MEMS) microphones. A MEMS microphone has many advantages such as high sensitivity, small package size, and low cost compared with an electret condenser microphone (ECM). However, the capacitive MEMS microphone, which is one of the most common type, has limitations in miniaturization and stiction issues between membrane and backplate. In this paper, a new design of SiNW-based MEMS microphone is presented, and a prototype of the microphone is fabricated to demonstrate the microphone fabrication process. The giant piezoresistive (GPZR) effects of SiNW and its very small size can be beneficial to the sensor miniaturization. In addition, stiction issues between membrane and backplate are prevented since backplate is unnecessary for the SiNW-based MEMS microphones. The presented fabrication process is much simpler than the fabrication process of the capacitive MEMS microphone in that only four mask layers are used. Furthermore, fabrication methods that require high cost such as using thin silicon-on-insulator (SOI) wafers or e-beam lithography process are unnecessary.