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Author: search.filters.author.Atthi, NithiSubject: search.filters.subject.Contour cavity

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    Fabrication of MEMS-based capacitive silicon microphone structure with staircase contour cavity using multi-film thickness mask
    (2019-02-01)
    Jantawong, Jirawat
    ;
    Atthi, Nithi
    ;
    Leepattarapongpan, Chana
    ;
    Srisuwan, Awirut
    ;
    Jeamsaksiri, Wutthinan
    In this work, a silicon capacitive microphone structure with a three-dimensional staircase style contour cavity (S-CTC) is developed using a newly developed Multi Film Thickness photo lithography process. This newly developed Multi Film masking process overrides the conventional wisdom in which the staircase style cavity is formed using multiple exposures of mask and multiple etchings of silicon. With this newly developed photo lithographic technique, a Multi Film Thickness (MFT) mask is fabricated with varying chromium film thicknesses such as 0, 4, 14, and 114 nm thick. The mask was then evaluated to fabricate a microphone structure with a three-dimensional staircase style cavity. Once the mask was patterned onto a substrate, a single dry etching of silicon was carried out and a desired three-dimensional stair cavity pattern was achieved. Surprisingly, our results show that a capacitive sensor with an S-CTC structure has an increased absolute capacitance value by an average of 30% in comparison to a conventional box cavity (BC) structure. This may indeed improve SNR as we anticipated. The capacitance value changed from 2.2pf to 2.9pf for the same dimension of devices. This promising technology renders an opportunity to improve the next generation of ultra-low-pressure sensors for microphone applications.
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    Fabrication of Contour Cavity Using Multi-Exposure Lithography for MEMS Capacitive Microphone
    (2018-07-02)
    Jantawong, Jirawat
    ;
    Atthi, Nithi
    ;
    Leepattarapongpan, Chana
    ;
    Jeamsaksiri, Wutthinan
    ;
    Austin, Anu
    This paper presents a novel technique to optimize a capacitive pressure sensor with multi-exposure dose lithography. As part of achieving high signal to noise ratio (SNR) in microphone, a new design was implemented. The new design defies the conventional wisdom of parallel plate theory and implement a concept of contour cavity (backplate) to follows the diaphragm deflection. This 3-dimensional contour cavity (CC) is fabricated by multi-exposure dose lithography with single silicon etching process. The CC structure with different etched depth of 0.65, 1.15, and 1.57 micron were fabricated by multi-exposure dose of 92, 120, and 210 mJ/cm<sup>2</sup>on 5.0 micron thick photoresist and single step etching with CF<inf>4</inf>/O<inf>2</inf>plasma (Si/PR etch selectivity: 1.3). Due to this novel contour cavity design, polysilicon membrane with 0.8 micron thick and a diameter of 930 micron structure produces the capacitance value of 2.88 pF, which is 28.6% higher than that of conventional parallel plate capacitive sensor.