Modelling and Optimisation of a Spring-Supported Diaphragm Capacitive MEMS Microphone

Abstract

Audio applications such as mobile communication and hearing aid devices demand a small size but high performance, stable and low cost microphone to reproduce a high quality sound. Capacitive microphone can be designed to fulfill such requirements with some trade-offs between sensitivity, operating frequency range, and noise level mainly due to the effect of device structure dimensions and viscous damping. Smaller microphone size and air gap will gradually decrease its sensitivity and increase the viscous damping. The aim of this research was to develop a mathematical model of a spring-supported diaphragm capacitive MEMS microphone as well as an approach to optimize a microphone's performance. Because of the complex shapes in this latest type of diaphragm design trend, analytical modelling has not been previously attempted. A novel diaphragm design is proposed that offers increased mechanical sensitivity of a capacitive microphone by reducing its diaphragm stiffness. A lumped element model of the spring-supported diaphragm microphone is developed to analyze the complex relations between the microphone performance factors and to find the optimum dimensions based on the design requirements. It is shown analytically that the spring dimensions of the spring-supported diaphragm do not have large effects on the microphone performance com pared to the diaphragm and backplate size, diaphragm thickness, and air-gap distance. A 1 mm 2 spring-supported diaphragm microphone is designed using several optimized performance parameters to give a -3 dB operating bandwidth of 10.2 kHz, a sensitivity of 4.67 mV/Pa (-46.5 dB ref. 1 V/Pa at 1 kHz using a bias voltage of 3 V), a pull-in voltage of 13 V, and a thermal noise of -22 dBA SPL.

Flexible Piezoelectric Acoustic Sensors and Machine Learning for Speech Processing

“…The condenser type microphones is widely commercialized acoustic sensor to detect sound signal by using the difference of capacitance between two conducting diaphragms . This capacitive sensors belong to the nonresonance type that exhibits the flat frequency response.…”

A MEMS-based shifted membrane electrodynamic microsensor for microphone applications

“…It is a transducer that converts the pressure input into electrical signal and is mostly used in communication, hearing-aid devices and vibration control systems (Ma and Man, 2002). Most microphone sensors are developed for audio applications, with frequency ranges from 20 Hz to 20 kHz and pressure level range from 20 μPa to 60 Pa. Sound pressure can be detected using many techniques such as piezoelectric (Horowitz et al., 2007), piezoresistive (Schellin and Hess, 1992), optic (Bilaniuk, 1997) and capacitive (Mohamad et al., 2010). The latter is considered to be the most common type among silicon microphone schemes because of its high sensitivity (∼mV/Pa), large bandwidth and low noise level (Ganji and Majlis, 2009; Huang et al., 2011).…”

A MEMS Condenser Microphone-Based Intracochlear Acoustic Receiver

“…Acoustic, mechanical, and electrical elements ( Fig. 2a) of a MEMS CMIC, such as the diaphragm, back plate, back cavity, and electrical capacity were represented by acoustic impedances with equivalent mass, stiffness and/or damping properties [30]- [33]. The relevant dimensions of the individual microphone elements, including the microtube size, had to be much smaller than the wavelength of the acoustic wave for such representations [34].…”