Reduced process temperature of vanadium dioxide films sputtered in reactive oxygen/hydrogen plasmas.

摘要

A significant factor limiting the wide spread use of thin VO{dollar}sb2{dollar} films is that they are currently processed at {dollar}sim{dollar}400{dollar}spcirc{dollar}C; above the softening temperatures of high transparency substrates, such as ZnS, ZnSe and polymer films. The latter are of interest for "smart" VO{dollar}sb2{dollar} window coatings.; The primary objective of this dissertation was to develop a process to synthesize VO{dollar}sb2{dollar} thin films at lower temperatures. The basic approach was to modify a process in which stable, amorphous, vanadium pentoxide {dollar}(alpha{dollar}-{dollar}rm Vsb2Osb5){dollar} films are obtained by sputtering the metal in an oxygen-reactive plasma. In the new two step process, hydrogen was introduced to reduce the {dollar}alpha{dollar}-{dollar}rm Vsb2Osb5{dollar} to {dollar}alpha{dollar}-VO{dollar}sb2.{dollar} The as-deposited {dollar}alpha{dollar}-VO{dollar}sb2{dollar} films were then crystallized in an inert gas at {dollar}sim{dollar}290{dollar}spcirc{dollar}C, the lowest yet reported. The quality of the films produced by this process was comparable to the best results produced by the previously reported, high temperature, film deposition processes.; A systematic study was conducted to determine the parameters of the two step process yielding the highest quality VO{dollar}sb2{dollar} films. The results showed that the best properties were obtained for films sputtered in reactive plasmas with a H2 pressure in the range of 0.5 to 3.0 mTorr and at deposition temperatures of 75 {dollar}sim{dollar} 250{dollar}spcirc{dollar}C. The as-deposited films were crystallized as VO{dollar}sb2{dollar} by annealing at 300{dollar}spcirc{dollar}C, either in flowing, or static N{dollar}sb2.{dollar} Films annealed in static N{dollar}sb2{dollar} were of comparable quality to those produced by high temperature processing. The role of H{dollar}sb2{dollar} in selecting the short range order of vanadium oxide was modeled as a heterogeneous catalytic reaction, initiated by the adsorption of reactants on the surface of the growing VO{dollar}sb{lcub}rm x{rcub}{dollar} film, and terminated by the desorption of product molecules. The control of the OH concentration through the formation and desorption of H{dollar}sb2{dollar}O was the decisive factor for the selection of the amorphous VO{dollar}sb2{dollar} phase.; In other experiments, as deposited {dollar}alpha{dollar}-VO{dollar}sb2{dollar} annealed in vacuum, crystallized to vanadium sesquioxide at 300{dollar}spcirc{dollar}C. This reduction of {dollar}sim{dollar}100{dollar}spcirc{dollar}C below existing processes, suggests that further studies be made of low temperature processed {dollar}rm Vsb2Osb3,{dollar} and other transition metal oxide films.