Abstract
New mobile devices need microphones with a small size, low noise level, reduced cost and high stability respect to variations of temperature and humidity. These characteristics can be obtained using Microelectromechanical Systems (MEMS) microphones, which are substituting for conventional electret condenser microphones (ECM). We present the design and modeling of a capacitive dual-backplate MEMS microphone with a novel circular diaphragm (600 µm diameter and 2.25 µm thickness) supported by fifteen polysilicon springs (2.25 µm thickness). These springs increase the effective area (86.85% of the total area), the linearity and sensitivity of the diaphragm. This design is based on the SUMMiT V fabrication process from Sandia National Laboratories. A lumped element model is obtained to predict the electrical and mechanical behavior of the microphone as a function of the diaphragm dimensions. In addition, models of the finite element method (FEM) are implemented to estimate the resonance frequencies, deflections, and stresses of the diaphragm. The results of the analytical models agree well with those of the FEM models. Applying a bias voltage of 3 V, the designed microphone has a bandwidth from 31 Hz to 27 kHz with 3 dB sensitivity variation, a sensitivity of 34.4 mV/Pa, a pull-in voltage of 6.17 V and a signal to noise ratio of 62 dBA. The results of the proposed microphone performance are suitable for mobile device applications.
Highlights
Microelectromechanical systems (MEMS) technology have allowed the development of microphones with characteristics such as a small size, low power consumption, reduced cost, high signal quality and good stability respect to variations of temperature and humidity [1,2]
Grixti et al [10] created a mathematical model of Microelectromechanical Systems (MEMS) microphone composed by a clamped square diaphragm (675 μm × 675 μm), which is based on the PolyMUMPs process
The novel design of a MEMS dual-backplate capacitive microphone supported by an array of fifteen polysilicon springs is presented
Summary
Microelectromechanical systems (MEMS) technology have allowed the development of microphones with characteristics such as a small size, low power consumption, reduced cost, high signal quality and good stability respect to variations of temperature and humidity [1,2]. Grixti et al [10] created a mathematical model of MEMS microphone composed by a clamped square diaphragm (675 μm × 675 μm), which is based on the PolyMUMPs process This microphone is supplied by a voltage of 6 V, achieving a sensitivity of 8.4 mV/Pa and a cut-off frequency of 10.5 kHz. Gharaei and Koohsorkhi [11] proposed an analytical model to design a MEMS microphone with a fungous-coupled diaphragm structure (460 μm diameter) that increased the diaphragm effective area, obtaining a parallel plates capacitor. Analytical and finite element method (FEM) models are developed to predict the electromechanical behavior of the proposed microphone
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