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ABSTRACT

The present work focuses on the preparation and characterization of Silicon

Carbide (SiC) and Aluminum Nitride (AlN) films prepared by RF magnetron

sputtering for micro-electro-mechanical systems (MEMS) application using their

respective ceramic targets. SiC and AlN films were selected respectively as structural

and piezoelectric materials. Sputtered SiC films have been reported for application as

protective coatings but their application as structural material has not been

investigated in significant manner. In the present work, we aim to produce low stress

SiC films with high Youngs modulus (E) and Hardness (H) values for structural

material in MEMS. Such SiC films could also be useful for high frequency

resonating MEMS. The objective of the present work is to prepare SiC films by RF

sputtering, preferably without external substrate heating. This is considered

important, if the MEMS are to be realized on low-cost substrates such as glass. The

residual stress was measured using wafer curvature technique. The sputtering process

was optimized for obtaining a low stress SiC films. The structural and mechanical

properties of these films were investigated. For this purpose, characterizations tools

such as: XRD, Fourier Transform Infrared Spectroscopy (FTIR) and nano-

indentation techniques are used. The chemical inertness of low stress SiC films in

buffered hydrofluoric acid (BHF), KOH / tetra-methyl-ammonium hydroxide

(TMAH), was investigated and it was observed that the films were stable in these

solutions for prolonged exposure. To demonstrate the feasibility of sputter deposited

SiC films for MEMS, suspended microstructures such as cantilever beams,

diaphragms, and bridges were fabricated using Si bulk micromachining process.

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For the AlN films, the objective was defined to prepare c-axis oriented AlN films

without external substrate heating by RF magnetron sputtering. FTIR was used to

study the Al-N bonds in the films. The films were characterized by XRD and TEM

(transmission electron microscopy) to investigate the preferred orientation. AlN films

with preferred (002) orientation were prepared on a variety of substrates by RF

magnetron sputtering using ceramic target. The c-axis orientation in the films is

achieved without external substrate heating when sputtering was carried out in Ar-N2

(1:1) ambient.

For applications as piezoelectric material in MEMS and other acoustic devices,

these films are required to be deposited on metal electrode. Therefore we investigated

the effect of various metal films such as: Al, Cr, Au-Cr on preferred orientation of

AlN films. The quality of c-axis oriented AlN films prepared by this method was

investigated for a chosen set of sputtering parameters using techniques such as UV-

VIS spectroscopy, PL (photoluminescence) spectroscopy, and SIMS (secondary ion

mass spectroscopy). The electrical resistivity of AlN films was found in the range of

1011

-1012

-cm for moderate fields (~50 kV/cm). Such high resistivity of these films

is essential for the application of AlN as a piezoelectric material. A prototype film

bulk acoustic resonator (FBAR) device was fabricated to demonstrate that the films

are suitable for acoustic / piezoelectric MEMS.

The thesis concludes by suggesting the scope of further research in this area.