A Novel MEMS Capacitive Microphone with Semiconstrained Diaphragm Supported with Center and Peripheral Backplate Protrusions

Abstract

Audio applications such as mobile phones, hearing aids, true wireless stereo earphones, and Internet of Things devices demand small size, high performance, and reduced cost. Microelectromechanical system (MEMS) capacitive microphones fulfill these requirements with improved reliability and specifications related to sensitivity, signal-to-noise ratio (SNR), distortion, and dynamic range when compared to their electret condenser microphone counterparts. We present the design and modeling of a semiconstrained polysilicon diaphragm with flexible springs that are simply supported under bias voltage with a center and eight peripheral protrusions extending from the backplate. The flexible springs attached to the diaphragm reduce the residual film stress effect more effectively compared to constrained diaphragms. The center and peripheral protrusions from the backplate further increase the effective area, linearity, and sensitivity of the diaphragm when the diaphragm engages with these protrusions under an applied bias voltage. Finite element modeling approaches have been implemented to estimate deflection, compliance, and resonance. We report an 85% increase in the effective area of the diaphragm in this configuration with respect to a constrained diaphragm and a 48% increase with respect to a simply supported diaphragm without the center protrusion. Under the applied bias, the effective area further increases by an additional 15% as compared to the unbiased diaphragm effective area. A lumped element model has been also developed to predict the mechanical and electrical behavior of the microphone. With an applied bias, the microphone has a sensitivity of −38 dB (ref. 1 V/Pa at 1 kHz) and an SNR of 67 dBA measured in a 3.25 mm ´ 1.9 mm ´ 0.9 mm package including an analog ASIC.

Ultra-sensitive graphene membranes for microphone applications

“…The mechanical sensitivity, defined as the membrane's displacement amplitude per unit sound pressure, scales inversely with the thickness and stress of the sensing membrane. 2 Complex fabrication techniques involving corrugated membranes 4,5 or not-fully supported membranes [6][7][8] have been implemented to reduce residual fabrication stress and boost sensitivity of thin MEMS membranes.…”

A Behavioral Non-Linear Modeling Implementation for MEMS Capacitive Microphones

“…The perforated unit cell model for the back plate is used to derive a curve fitting polynomial to account for the fringing field capacitance [12]. A hexagonal symmetry is utilized along with the assumption that no bending occurs within the unit cell.…”

Ultra-sensitive graphene membranes for microphone applications

“…The mechanical sensitivity, defined as the membrane's displacement amplitude per unit sound pressure, scales inversely with the thickness and stress of the sensing membrane. 2 Complex fabrication techniques involving corrugated membranes 4,5 or not-fully supported membranes [6][7][8] have been implemented to reduce residual fabrication stress and boost sensitivity of thin MEMS membranes.…”