The fabrication and characterisation of metal oxide thin films for microelectronic and optical applications
Creators: name: Field, Matthew
Publisher: name: RMIT University
Year: 2024

description: Metal oxide thin films are the subject of considerable research due to their novel optical and electrical properties which make them suitable for use in many applications. These applications include gas sensors, solar cell arrays, anti dazzling rear view mirrors, smart windows, gate dielectrics, semiconductors and many more. The possibilities for new metal oxide based materials is forever growing with the introduction of novel deposition methods which allow precise control of the deposition parameters and the ability to dope in order to tailor properties. The conditions used for the deposition of these coatings has an influence on the microstructure which in turn plays an important role in determining physical properties, such as the optical transmission and electrical conductivity. In addition, for many metal oxide materials the structure-property relationship is not well understood. The aim of this thesis was two-fold. Firstly, to deposit some metal oxide thin film coatings using several physical vapour deposition techniques and characterise their microstructure and physical properties. Secondly, to make a comparison between films deposited using different techniques to determine how the properties of a film depend on the conditions under which they are formed. <br><br>To achieve these aims, tungsten oxide, zinc oxide doped with aluminium (also known as aluminium zinc oxide - AZO) and hafnium oxide coatings were deposited and the microstructure and physical properties were investigated. For tungsten oxide deposition, films were deposited using pulsed magnetron sputtering and pulsed cathodic arc. It was found that films deposited using magnetron sputtering were highly disordered. In contrast, those deposited with cathodic arc were a highly ordered and exhibited a tetragonal phase, usually only observed at high temperatures. <br><br>In the case of AZO, films were deposited using pulsed cathodic arc, pulsed magnetron sputtering and high power impulse magnetron sputtering (HIPIMS). The pulsed cathodic arc films were found to have both good transmittance in the visible region and the best resistivity of all of the samples. <br><br>It was found that magnetron and HIPIMS produced films that exhibited non-uniform properties across their surface due to in situ oxygen bombardment during deposition. This undesirable effect was eliminated by incorporating a novel magnetic filter into the deposition setup which acted to improve both the crystallinity and the resistivity. This thesis also performed the first comprehensive investigation of hafnium oxide films prepared using a filtered cathodic vacuum arc. Samples deposited at high substrate biases were found to damage readily which made them electrically leaky. Samples deposited at room temperature were found to have a disordered microstructure and had a good electrical breakdown. At elevated temperatures the crystallinity of the samples increased, resulting in a microstructure containing large monoclinic crystals. However, it was also found that the electrical breakdown worsened at elevated temperatures, in agreement with other researchers who also find that hafnium oxide films with disordered microstructure have the best electrical characteristics.<br><br>Ab initio calculations of the near edge structure found in x-ray and electron loss edges were found to be a powerful way of distinguishing between the phases of tungsten oxide.