A novel MEMS capacitive microphone using spring-type diaphragm

In this paper, we present a new design of diaphragm that supported by frog arms for MEMS capacitive microphone structure. The proposed diaphragm reduces the air damping and diaphragm stiffness to improve the microphone sensitivity. The behaviour of the microphones with clamped and supported diaphragm by frog arms are analysed and simulated using finite element method (FEM). The structure has a perforated aluminium diaphragm with a thickness of 3 mu m, a diaphragm size of 0.5mmx0.5mm, and an air gap of 1 mu m. According to the results, the mechanical sensitivity of the new microphone is 9.893nm/Pa and pull-in voltage is 2.25V whereas the clamped one with same diaphragm size has a mechanical sensitivity of 0.309nm/Pa and pull-in voltage of 44.6V. By introducing the frog arms around the diaphragm, the mechanical sensitivity increased 32 times. The results also yield a capacitance sensitivity of 0.15fF/Pa for clamped microphone and 27.45fF/Pa for supported one with frog arms. The pull-in voltage of the supported microphone by frog arms has decreased about 95% compared with clamped one.