Design of Perforated Membrane for Low-Noise Capacitive MEMS Accelerometers

A method is presented for designing a thick membrane with several thousand perforations suitable for low-noise capacitive micro-electro-mechanical systems (MEMS) accelerometers. Although a membrane with two-step perforations shows good noise density performance, it is difficult to simulate mechanical noise using the conventional method because there are too many perforations, which makes the structure of the membrane complicated. The proposed method is based on the assumption that the number of perforations is infinite and that there are symmetric planes between the perforations. This assumption greatly reduces computational complexity because the simulation model is simplified in the region around a perforation. We fabricated MEMS resonators with a two-step perforated membrane and evaluated the accuracy of the simulation results. The measured Q values of the fabricated resonators were in good agreement with the calculated results. Using this design method, we optimized the structure of a membrane with two-step perforations and fabricated a capacitive MEMS accelerometer. It showed excellent low-noise density (less than 15 ng/Hz(1/2)).