Acoustic analysis and fabrication of microelectromechanical system capacitive microphones

Abstract

This paper presents a microelectromechanical system (MEMS) capacitive microphone fabricated by using a combination of surface and bulk micromachining techniques equipped with favorable integrated complementary metal-oxide semiconductor capability. Through the proposed equivalent circuit model for the packaged microphone, optimal diaphragm diameter, diaphragm thickness, backplate height, air gap, front chamber volume, back chamber height, and acoustic hole fraction have been determined by analyzing and simulating the capacitive microphone. Consequently, this design model can optimize choice of materials, microphone size, and microphone performance. All parameters for the analysis have been experimentally measured for the microphone. To verify our analysis, the microphone sensitivity has been experimentally measured by pulse electroacoustics with the software SOUND CHECK in an anechoic box. The simulation and experimental results for sensitivity of the microphone follow each other within a range of 2 dB. Moreover, the measured specifications indicate that the packaged microphone has notably high sensitivity (−42±3 dB V/Pa at 1 kHz), low power consumption (<250 μA), high S/N ratio (>55), and low distortion (<0.5%).

A Review of MEMS Capacitive Microphones

“…Miao et al [67] suggested that it could be tuned by monitoring the process parameters during the fabrications of diaphragm, such as higher annealing temperature and lower base pressure. Some groups employed implantation method on the material, for example N 2 ion [36], boron ion [42,56,73], and phosphorous ion [27,88]. These ion implantation changes the stress gradient of the diaphragm due to the mismatch between the coefficients of thermal expansions (CTE) of each material.…”

“…The positively charged diaphragm (p-type semiconductor) and negatively charged backplate (n-type semiconductor) act as positive and negative terminals, respectively. Therefore, as can be seen from Table 1, most researchers employed Si and poly-Si as backplate material [39,43,47,67,88,95]. Few groups did opt for metals instead.…”

Design and characterization of high sensitive MEMS capacitive microphone with fungous coupled diaphragm structure

“…Lumped element modeling has traditionally been used for analysis of acoustic liners (Horowitz et al 2006;Her et al 2008). The acoustic properties of the microphone structure can be modeled using lumped element modeling (LEM), in which the distributed properties of the microphone are represented by set of lumped elements (Rossi 1988).…”

Implementation of the CMOS MEMS Condenser Microphone with Corrugated Metal Diaphragm and Silicon Back-Plate

“…Moreover, the equivalent circuit for the proposed MEMS microphone is shown in Figure 3 . The diaphragm, air gap, vent hole, back-plate, and back chamber are described by the complex damping, mass, compliance system, and assembled in an acoustical circuit [ 9 – 12 ]. This equivalent small signal circuit containing the acoustic, mechanical, and electrical component can well describe the behaviors of the MEMS microphone by PSPICE.…”