Electronic Theses and Dissertations

1991

Dissertation

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Physics, Condensed Matter.

CC BY-NC-ND 4.0

Abstract

Thin films of barium titanium silicate $(\rm Ba\sb2Si\sb2TiO\sb8)$ are grown on crystalline (100) Si at substrate temperatures raging from 750 to 955$\sp\circ$C by the radio-frequency triode sputtering technique. The chemical composition, microstructure, physical properties, and growth conditions of the deposited films are investigated by dc and high-frequency dielectric measurements, wavelength dispersive and energy dispersive x-ray spectrometries, x-ray diffraction spectrometry, and optical and scanning electron microscopies. The results of the x-ray diffraction analysis show that the $\rm Ba\sb2Si\sb2TiO\sb8$ films deposited at the optimum condition of substrate temperature of 845$\sp\circ$C, 4 cm source-substance distance, 50 W rf power, and 1.2 $\times$ 10$\sp{-3}$ torr pressure of Ar, are highly c-axis oriented. The as-deposited films are smooth, glossy, polycrystalline films, exhibiting a bulk resistivity range of 10$\sp6\ \Omega\cdot$cm, and an isotropic surface resistivity of 1.5 $\times$ 10$\sp3\ \Omega\cdot$cm. The relative dielectric constant is 0.05, and the dielectric loss is lower than 1.0, in the frequency band 9 $\sim$ 1000 MHz. The high-frequency impedance of BST films, which is typical for piezoelectric materials, gives a minimum impedance frequency of 9.0 MHz and a series resonant frequency of 9.5 MHz. Optical and SEM observations show that the film texture is dependent on the substrate conditions. The non-liquid-like grain coalescence of the $\rm Ba\sb2Si\sb2TiO\sb8$ grains is characteristic of a strong film-substrate interaction. The grain growth kinetics obtained from "short-time" sputtering gives an initial lateral grain growth rate of 770 nm/min at 845$\sp\circ$C, which decreases with the grain size. The initial film growth rate in the direction of thickness, measured from SEM micrographs, is 1.95 nm/min, and decreases with sputtering time. The activation free energy for grain growth is 359 $\pm$ 30 KJ/mol for the initial stage, decreasing to 148 $\pm$ 20 KJ/mol for the final stage. The variation of the grain growth rate and the activation energy with grain size is the result of a combined nucleation and growth mechanism in the initial stage of the film growth, and a coalescence-dominated growth mechanism at longer sputtering time and at higher temperature. Film orientation is sensitive to the supersaturation adjacent to the film surface, which depends on the source-substrate distance and substrate temperature. The effect of the substrate temperature on the orientation of the film is investigated over a wide temperature range using (100) and (111) Si substrates. Several orientations for the BST films, including an amorphous state, are obtained with increasing substrate temperature. This is discussed in relation to the atomic plane density and the energetics for the deposition process.Dept. of Mechanical, Automotive, and Materials Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1992 .L595. Source: Dissertation Abstracts International, Volume: 54-05, Section: B, page: 2572. Thesis (Ph.D.)--University of Windsor (Canada), 1991.

COinS