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Dissertation/Thesis Abstract

SiC Thin-Films on Insulating substrates for Robust MEMS Applications
by Cheng, Lin, Ph.D., University of Cincinnati, 2003, 168; 10857159
Abstract (Summary)

MEMS applications require that large area of uniform SiC films is formed on insulating substrates or sacrificial layers. For electrically controlled MEMS devices, in-situ N2-doped 3C-SiC thin-films have been grown by low-pressure chemical vapor deposition (LPCVD) on low-stress, amorphous Si3 N4/p-Si(111) substrate using the single organosilane precursor trimethylsilane [(CH3)3 SiH]. The effects of N2 flow rate and growth temperature on the electrical properties of SiC films were investigated by Hall Effect measurements. The electron carrier concentration is between 1017~1018 /cm3. The lowest resistivities at 400 K and 300 K are 1.12x10-2 and 1.18x10-1 Ω•cm, respectively. The corresponding sheet resistances are 75.02 and 790.36 Ω/square. The SiC film structure was studied by X-ray diffraction (XRD). The 3C-SiC films oriented in the <111> direction with a 2&thetas; peak at 35.5° and line widths between 0.18°~0.25° were obtained. The SiC-Si3N 4 interface is very smooth and free of voids. To pattern the SiC films into the desired structural shapes, selective etching is required. The inductively coupled plasma (ICP) etching of 3C-SiC films was then examined in both NF 3/Ar and Cl2/Ar mixtures. Two different mask materials (ITO and Shipley 1818 photo-resist) were compared. The effects of RF power, DC bias, ICP power and gas flow ratio on etch rates have been discussed. Furthermore, a novel fiber-optic temperature sensor, which is rugged, compact, stable, and can be easily fabricated, has been developed by using the SiC thin-film grown on sapphire substrate. The film thickness was optimized to 2~3 μm, while the optimal 3MS flow rate ranged from 35~40 sccm to produce an optically flat SiC film. The sensors were operated at temperature from 22°C to 540°C. The shifts in resonance minima versus temperature from the reflection spectra fit a linear function, giving a relative temperature sensitivity of 1.9x10-5/°C. The capability of providing a ±3 °C accuracy was discovered at 532°C in a wide-open ambient, through a 14-days operating life.

Indexing (document details)
Advisor: Steckl, Andrew J.
School: University of Cincinnati
Department: Electrical Engineering
School Location: United States -- Ohio
Source: DAI-B 79/10(E), Dissertation Abstracts International
Subjects: Electrical engineering
Keywords: Fabry-perot interferometer, Icp etching, Lpcvd, Mems, Sic on insulating substrate
Publication Number: 10857159
ISBN: 978-0-438-02275-1
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