Fabrication, characterisation and modelling of electronic devices based on amorphous metal-oxide and carbonaceous materials
Creators: name: Tran, Hiep Le Ngoc
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400908
subject: Microelectronics

description: This thesis describes the deposition, characterisation and device applications of amorphous zinc tin oxide (a-ZTO) and carbon-based materials using energetic deposition techniques. The study aimed to explore the suitability of this growth method in producing highquality carbon and a-ZTO films for device applications. Technology Computer Aided Design (TCAD) simulations were also conducted in tandem with experiments to identify critical parameters affecting device behaviour and to provide guidance for improved device performance.<br><br> Firstly, electrical carbon contacts to n-type 6H-SiC were energetically deposited from a filtered cathodic vacuum arc (FCVA) at room temperature and elevated temperature with low and high biases. Lower energy (&lt; 100 eV) in the carbon flux resulted in resistive amorphous carbon contacts. As the deposition energy and sp2 bonding (graphitic) fraction were increased, an oriented graphitic microstructure developed and rectifying electrical characteristics emerged. TCAD simulations revealed the effects of interfacial layers and contact work functions on the device performance and suggested that the rectification ratios of C/6H-SiC Schottky diodes could be increased by improving the lateral homogeneity of the junctions and/or by controlling the thickness of interfacial layers.<br><br> Secondly, thin films of amorphous zinc tin oxide (a-ZTO) were energetically deposited using high power impulse magnetron sputtering (HiPIMS). HiPIMS and DC magnetron sputtering modes were enabled to co-deposit an a-ZTO layer with Zn:Sn ratio that varied laterally across a 4-inch diameter sapphire substrate. Electrical, structural and optical properties of the films were investigated as a function of composition. The as-deposited films were found to be amorphous, transparent and highly resistive with little variation in the Zn:Sn ratios. Annealing in the presence of hydrogen yielded improved film conductivity and measured carrier concentrations of ~ 1017 cm-3 . Hall mobilities of up to 13 cm2 /V.s were also measured in the ntype films. These findings suggest that HiPIMS can produce dense, high quality a-ZTO suitable for device applications.<br><br> As a transparent amorphous conducting oxide with high transparency and good electron mobility, a-ZTO has proven applications in interconnects and thin film transistors. In this thesis, the potential for this material in ‘next-generation’ signal processing devices is discussed. Specifically, the ability of the material to support resistive switching and memristive phenomena was investigated in lateral memristors on HiPIMS a-ZTO. The transport mechanisms and conductance of Ag/a-ZTO memristors were found to depend on prior activity and on the imposed current limit, mimicking biology synaptic plasticity. After microscopy, the switching mechanism was attributed to nanoscale filaments formed between the electrodes. These filaments were subject to Rayleigh instability and exhibited relaxation times determined by their effective radii.