AVS 53rd International Symposium
    MEMS and NEMS Tuesday Sessions
       Session MN-TuM

Paper MN-TuM4
Characterization of APCVD and LPCVD Based Polycrystalline 3C-Silicon Carbide Resonators

Tuesday, November 14, 2006, 9:00 am, Room 2007

Session: Material Aspects of MEMS and NEMS
Presenter: W.C. Chang, Case Western Reserve University
Authors: W.C. Chang, Case Western Reserve University
C. Zorman, Case Western Reserve University
M. Mehregany, Case Western Reserve University
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Silicon Carbide is a promising material for RF MEMS due to its mechanical robustness, chemical inertness and high Young's Modulus-to-density ratio. While single crystalline SiC films are used for high quality devices, many MEMS devices do not require such high crystalline quality and therefore can use polycrystalline SiC films. Polycrystalline SiC can be grown at a lower temperature than single crystal films, (at or below 900°C by LPCVD), which makes the process more compatible with conventional MEMS processes. Furthermore, the deposition does not depend on a crystalline template, as it can be deposited on any substrate, whether single crystalline, polycrystalline or amorphous. This advantage enables polycrystalline SiC to be used in more complex micromechanical structures than single crystalline SiC. This paper demonstrates poly-SiC folded beam resonators fabricated by atmospheric pressure chemical vapor deposition (APCVD) and low pressure chemical vapor deposition (LPCVD). APCVD resonators were made from films grown at 1280°C using SiH@sub 4@ and C@sub 3@H@sub 8@ as precursors. SiO@sub 2@ and poly-Si were used for isolation and sacrificial layers, respectively. The LPCVD resonators were made from films deposited at 900°C using SiH@sub 2@Cl@sub 2@ and C@sub 2@H@sub 2@ as precursors. The resonator design used SiO@sub 2@ as an isolation and sacrificial layer. The devices were driven and measured by an Agilent 4395A network analyzer via a transimpedance amplifier under a reduced pressure of 30uTorr. The measured quality factors are about 22k and 10k for APCVD and LPCVD grown lateral resonators respectively. The quality factors of the poly-SiC flexural-mode resonators are the highest reported values by electrical measurement so far. To compare the intrinsic loss of the two folded beam resonators, XRD was used to compare the average grain size of poly SiC. The estimation for APCVD-grown poly SiC is 65nm and 43nm for LPCVD-grown poly SiC.