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A Concave-Patterned TiN/PECVD-Si3N4 /TiN Diaphragm MEMS Acoustic Sensor Based on a Polyimide Sacrificial Layer
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- Issue Date
- 2015-12
- Citation
- Journal of Micromechanics and Microengineering, v.25, no.12, pp.1-13
- ISSN
- 0960-1317
- Publisher
- Institute of Physics (IOP)
- Language
- English
- Type
- Journal Article
- Abstract
- 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.
- KSP Keywords
- Acoustic Sensor, Active area, Analytical model, Back-plate, Capacitance model, Capture module, Dynamic responses, Electric field method, FEM simulation, Front-End, Lumped parameters