Study On SnO₂and NiO Thin-film Transistors

Recently, thin film transistors (TFTs) based on wide bandgap oxide semiconductor havebeen extensively investigated because of their high electron mobility and low processingtemperature, making them compatible with flexible substrates and opening the potential forlow production cost. In this thesis dissertation, we mainly study the preparation of metaloxide thin film transistors, the n type SnO2thin film transistors by spray pyrolysis and p-typeNiO thin film transistors by Rf magnetron sputtering, in order to achieve the preparation ofcomplementary circuit of the device.SnO2is the intrinsic n-type wide band gap semiconductor material and the directbandgap at room temperature is about3.6~4.3eV. And SnO2are widely used in many fieldsbecause of a high transmittance in the visible light region, stable chemical and physicalproperties. SnO2thin films were deposited on SiO2/Si substrates by a simple and low-costspray pyrolysis technique with stannic chloride (SnCl4:5H2O) as precursors. We analyzed theimpact of different annealing temperature treatment on the crystal structure of the samplequality, optical transmittance, optical band gap properties, and electrical properties. Based onthe optimized sputtering parameters, SnO2-TFTs with different annealing temperature,spraying time and nozzle-to-substrate distance were fabricated on SiO2/Si substrates using topcontact configuration with bottom gate. It was found that the TFT exhibited a good electricalperformance when the annealing temperature was450℃, nozzle-to-substrate distance was5cm, and spraying time was5min. Previous studies have suggested that SnO2films depositedby physical vapor deposition contain native defect such as oxygen vacancies and thus highresidual electrons. The carrier concentration is too high to be not suitable for the channel layer.In this thesis, SnO2thin films were deposited by a low-cost spray pyrolysis technique. Carrier concentration is suitable for the transistor device. The SnO2-TFTs exhibit excellent saturationand pinch-off characteristics with the mobility of about0.37cm2V-1s-1, current on-off ratio of106, a threshold voltage of-2V and a subthreshold voltage swings of2V/dec. The current isless than the drain current by more than six orders of magnitude, which guarantees that thedevice performance would not be affected by the leakage. The influence of visible lightirradiation on the electrical performance of the device was also investigated. The results showthat output characteristic is hardly affected, indicating the potential application for transparentelectronics.NiO is a direct wide band-gap semiconductor materials, and the band gap is between3.6~4.0eV at room temperature. NiO thin films were deposited on SiO2/Si substrates by RFmagnetron sputtering technique. We analyzed the impact of different sputtering power, gasratio of Ar/O2and pressure on the crystal structure of the sample quality, optical transmittance,optical band gap properties, and electrical properties. TFTs with NiO channel layer depositedthrough RF sputtering were fabricated using metal shadow mask. Output characteristicsindicated that the TFTs follow p-type standard field-effect transistor characteristics.