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학술지 A Concave-Patterned TiN/PECVD-Si3N4 /TiN Diaphragm MEMS Acoustic Sensor Based on a Polyimide Sacrificial Layer
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저자
이재우, 전주현, 제창한, 김이경, 이성규, 양우석, 이정선, 이상국
발행일
201512
출처
Journal of Micromechanics and Microengineering, v.25 no.12, pp.1-13
ISSN
0960-1317
출판사
Institute of Physics (IOP)
DOI
https://dx.doi.org/10.1088/0960-1317/25/12/125022
협약과제
15ZB1500, 환경 및 사용자 적응형 MEMS 마이크로폰 솔루션 개발, 양우석
초록
In this paper, we present a concave-patterned TiN/PECVD-Si3N4 /TiN diaphragm micro-electro-mechanical system (MEMS) acoustic sensor based on a polyimide sacrificial layer. The use of the spin-coated polyimide eliminates the additional Al pad process of conventional device fabrication due to simple O2 ashing to release the sacrificial layer, simplifying the photolithography process. Also, to adjust the acoustic sensor for a bottom-ported package, its diaphragm was implemented to be placed over the back-plate. The TiN/PECVD-Si3N4/TiN multi-layer diaphragm was formed with the stress controllability of PECVD-Si3N4 from -162 MPa to +109 MPa. Furthermore, a parallel-plate capacitance model on the basis of an approximately linearized electric field method (ALEM) is proposed to evaluate the capacitance of two plates. The modelled capacitance showed less than 3.7% error in FEM simulation, demonstrating the validity of the proposed model. At a zero-bias voltage, the effective intrinsic and parasitic capacitances in the active area were 1.656 pF and 0.388 pF, respectively. Moreover, with a pull-in analytical model by using ALEM, the effective tensile stress for the diaphragm was extracted to +31.5 MPa, where the pull-in voltage was 10.7 V. In succession, the dynamic response for the open-circuit sensitivity was modelled with an equivalent circuit model based on lumped parameters. The measured open-circuit sensitivity of -45.1 dBV Pa-1 at 1 kHz with a bias of 9.6 V was only slightly different from the modelled sensitivity of -45.0 dBV Pa-1. Thus, these results demonstrate that the proposed sensor is suitable for a front-end voice capture module.
키워드
acoustic sensor, ALEM, MEMS, polyimide sacrificial layer
KSP 제안 키워드
Acoustic Sensor, Active area, Analytical model, Back-plate, Capacitance model, Capture module, Dynamic responses, Electric field method, FEM simulation, Front-End, Lumped parameters