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Low temperature fabricated condenser microphone with stress released membrane

Authors Zhu, Ruiqing
Issue Date 2007
Summary This thesis will focus on a condenser microphone on single Si wafer. Due to the demand of the whole market of low cost, high performance and IC integrated MEMS microphone, our goal is to create a high sensitivity acoustic-mechanically functional microphone by only using low temperature fabrication process. The temperature of the whole fabrication process is below 300°C, which makes the whole process can be integrated with CMOS circuits and is low cost without using any high temperature process equipment. Using CR-106 R to reduce the parasitic capacitance and the stress released structure of the membrane sealed by parylene to obtain high sensitivity of acoustic signal makes better performance of the microphone than previous designs. Diaphragm of with stress-released structure made of Ti is designed and membrane with 300μm is studied. Different designs of membranes are simulated to see how the diaphragm responds as part of a mechanical part. By using different sized acoustic holes with different holes spacing, along with different membrane thicknesses, and a geometrical study can be performed. In the geometrical study was a static analysis of different membrane thicknesses in motion under pressure by using the finite element model (FEM) software COVENTORTM. The behavior of the parylene sealed membrane is discussed and the mechanical and acoustic effect of this parylene layer is shown from summarization of the FEM analysis results. In this study, the diaphragm is deposited and patterned by using lift off process. The structure of the backplate with acoustic holes was patterned by copper electro-plating with thick photoresist mold. The gap between two plates is released by remove of sacrificial layer of AZ 6800. The KOH etch protection layer is Ge and SEM pictures of the backside etch holes will be shown. Dielectric constant testing by using mercury probe is discussed in Chapter 4. Testing set up is described then. The C-V testing and the acoustic testing results are compared with the simulation results. The conclusion and the suggested future work are discussed in the last chapter. Appendix of process flow and recipe of different kinds of photoresist and simulation programs are summarized for reference.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007
Language English
Format Thesis
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