A Miniature Silicon Condenser Microphone Improved with a Flexure Hinge Diaphragm and a Large Back Volume
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A Miniature Silicon Condenser Microphone Improved with a Flexure Hinge Diaphragm and a Large Back Volume H. J. Kim, S. Q Lee, J. W. Lee, S. K. Lee, and K. H. Park Electronics and Telecommunications Research Institute, 161 Gajeong-dong, Yuseong-gu, Daejeon, 305-700, Korea, Republic of ABSTRACT We have developed a miniature silicon condenser microphone improved with a spring supported hinge diaphragm and a large back volume, which is designed in order to increase sensitivity of microphones. MEMS Technology has been successfully applied to miniature silicon capacitive microphones, and we fabricated the smallest condenser silicon microphone in the presented reports. We used the finite-element analysis (FEA) to evaluate mechanical and acoustic performances of the condenser microphone with a flexure hinge diaphragm. From the simulation results, we confirmed that the sensitivity of a flexure hinge diaphragm can be improved about 285 times higher than a flat diaphragm. The first and second modes occurred at 15,637Hz and 24,387Hz, respectively. The areas of the miniature condenser microphones with a hinge diaphragm are 1.5 mm x 1.5 mm. We measured the impedance characteristics and sensitivities of the fabricated condenser microphones. The sensitivities of microphones are around 12.87 µV/Pa (-60 dB ref. 12.5 mV/Pa) at 1 kHz under a low bias voltage of 1 V, and the frequency response is flat up to 13 kHz.
INTRODUCTION Today, MEMS technology has been successfully applied to miniature silicon capacitive microphones [1-3], a lot of research has been published in order to achieve high performance miniature silicon microphones. Most miniature microphones are adopted by diaphragm-based capacitive type, i.e., condenser microphones and electret microphones because they have the flat frequency response in broad bandwidth, high SNR (signal-to-noise ratio), high sensitivity, low power consumption, and large quantities of manufacture, as compared with other types of microphones as like piezoelectric or piezoresistive microphones [4-6]. A typical silicon condenser microphone consists of a diaphragm, a rigid backplate, an air gap, electrodes and a back volume. And the sensitivity of the condenser microphone is determined by the electrical field strength exerting across the capacitor gap, the deformation (deflection) of diaphragm and a large air damping of back volume. Thus, to obtain high sensitivity in broad bandwidth, the diaphragm has to be designed to be flexible more and the backchamber has to have larger volume. So far, an important number of corrugated diaphragms and large backchamber designs have been introduced in order to achieve higher sensitive condenser microphone [7-9]. This paper presents a miniature condenser microphone with a spring supported hinge diaphragm and a large back volume, which contributes to high sensitivity and flat frequency response, even though the small diaphragm diameters of 500 µm.
EXPERIMENT This paper presents a miniature silicon condenser microphone with a flexure hinge diaphragm and a
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