Design and modeling of a frog-shape MEMS capacitive microphone using SOI technology

Abstract

In this paper, a novel micro electro mechanical systems (MEMS) capacitive microphone is designed and modeled using SOI technology. We present static linear spring constant analysis of the supported plate by frog arms. Then, we develop equations to determine pull-in voltage, resonance frequency and open circuit sensitivity based on calculation of spring constant for the proposed microphone. The mechanical model of the structure is extracted and the mathematical equations for a description of microphone behavior is obtained. This structure is presented to improve the sensitivity with the minimized microphone size. In this structure, due to the uniform deflection of the diaphragm and using the low-K structure, the supply voltage is decreased. The perforated diaphragm of this microphone is supported by frog-shape arms on its two sides. These arms around of diaphragm decrease the stiffness and air damping of the microphone. The behavior of this microphone is also analyzed by the finite element method (FEM). The structure has a diaphragm thickness of 5 µm, a diaphragm size of 0.3 mm × 0.3 mm, and an air gap of 1 µm. The Proposed microphone is simulated with Intellisuite software. According to the results, the new microphone has a sensitivity of 2.248 mV/Pa and pull-in voltage of 9.5 V. For validation of modeling, a comparison between calculated and simulated pull-in voltage, open circuit sensitivity and the resonance frequency are presented. The results show that the analytical equations for description of microphone behavior have a good agreement with simulation results. The proposed MEMS capacitive microphone is one of the best structures in performance, despite its small dimensions.