Investigation of Indium Tungsten Oxide Thin Film Fabricated by RF Sputtering System and Their Applications

Abstract

In this thesis indium tungsten oxide (IWO) is deposited by RF magnetron sputtering The IWO film properties are discussed in detail under different processing ambiences Afterwards the deposited IWO thin films were used as channel layer for UV photodetectors and thin film transistors (TFTs) Analyses were then carried out and discussion on the device characteristics was contained First the RF sputtering system was manipulated to grow films under various gas partial pressures Film properties were investigated thoroughly in terms of three aspects which were optical structural and surface/depth element analyses The optical analysis results showed that the transmittance in the visible light region were 80% and the energy bandgap was about 3 13-3 39 eV in correspondence In structural analysis the X-ray diffraction analysis (XRD) revealed that while the oxygen flow ratio of the film increased the crystalline phase and the peak intensities became apparent After annealing processes the peak intensities were much more obvious than the as-deposited IWO thin films The diagram generated by atomic force spectroscopy (AFM) showed the RMS values of IWO thin films are reduced after annealing processes and it indicated that annealing could improve the surface roughness In material element analysis the X-ray photoelectron spectroscopy (XPS) results suggested that the oxygen flow ratio rising from 2% to 10% the 6% IWO thin films had the least oxygen vacancies Second the IWO thin films were applied to UV photodetectors By adjusting oxygen flow ratio and annealing temperature the investigation was made to compare the effects toward IWO devices As the oxygen flow ratio increased the dark current was effectively suppressed At the oxygen flow ratio of 10% the dark current was 5 88*10-12 A the on-off current ratio was 4 56*10^4 the photoresponsivity was 1 9*10^(-2) A/W and the rejection ratio was 2 68*10^4 With post-annealing treatment the electron carriers in the IWO thin film were significantly rising causing the devices to excessive current and degrading the device performances Third IWO TFTs with silica (SiO2) as the gate dielectric layer were realized With the adjustments on oxygen partial pressures as well as annealing temperature the best parameters were utilized The transfer characteristics of optimized IWO TFTs at the room temperature make the results in a field effect mobility of 0 23 cm^2/V?s threshold voltage of 0 4 V subthreshold swing of 0 45 V/decade and on-off current ratio of 2 8 × 10^4 With post-annealing procedures the electron carriers in the IWO thin film were significantly increasing for 4 orders leading the devices to excessive current and degrading the overall device performances Therefore the IWO devices did not make improvement after annealing treatment At the last thin film transistors were operated under light illumination for examining performance The rejection ratio of IWO phototransistor was about 6 06*10^3 at the bias voltage of -2 V

Date of Award	2018 Jul 9
Original language	English
Supervisor	Shoou-Jinn Chang (Supervisor)