Research On Thin Film Transistors With Hafnia/Hafnium Oxynitride Gate Dielectrics And Metal Oxide Semiconductors

Thin film transistors (TFTs), as the core components of liquid crystal display, play an important part in improving display quality and enlarging display domain of flat panel display devices. Traditional TFTs use hydrogenated amorphous silicon as active layer, which is not compatible with the need of modern display field. Hydrogenated amorphous silicon TFTs has low mobility (-1 cm2/V·s) and high price, in addition, sensitive to visible light. These drawbacks make it is urgent to develop new TFTs adapted to modern life. The thesis research on the way to improve TFT characteristic from three aspects, such as source/drain electrodes, active layer and dielectric, which were the main components of TFTs.Source/drain electrodes were the components for TFTs'current output, which connect active layer with outer circuits. And it is the key factor for TFTs work efficiently that the contacts between active layer and electrodes are ohm type and the contact resistivity is low enough. In addition, since TFTs'current flows to outer circuits through electrodes, the resistivity of electrodes it selves can not be too large. If adapting Hf-N thin films with low work function and low electrical resistivity as source/drain electrodes in ZnO TFTs, the active layer ZnO and Hf-N could form ohm type contact, so as to obtain low contact resistivity. ZnO TFTs were fabricated following the above route. ZnO TFTs obtain an output current of 1.95μA, field effect mobility of 1.56 cm2/V·s and on/off ratio of-4×102.Active layers in TFTs generate current channel by applying voltage on TFTs' gate electrode. Metal oxide semiconductors are transparent in visible spectrum and have high field effect mobility, which make them important for transparent electronics. The thesis proposed a method for fabrication of InGaZnO (IGZO) thin film by pulsed laser deposition. The bandgap of the deposited IGZO thin films were in the range of 3.50 eV-3.61 eV, and the optical transmission of the films were above 80% in visible spectrum. The resistivity of the films deposited at room temperature were in the range of 103-104Ω·cm, while the films deposited at 400℃were-10-2Ω·cm. The highest mobility of the IGZO thin films is 54 cm2/V·s. The IGZO TFTs with high-κ gate insulator exhibited saturated current of 0.14 mA, field effect mobility of 5.8 cm2/V·s and on/off ratio of 2×105.The electrical characteristic of gate insulator and interface quality between active layer and dielectric layer affected the threshold voltage, subthreshold swing and mobility of TFTs heavily. The thesis fabricated high-κHfOχNy, thin films by reactive radio frequency magnetron sputtering. The optical and electrical characteristics were investigated in detail. It is observed that N doped into HfO2 could increase the crystallization temperature and improve the interface quality when contacting with other films. The IGZO TFTs with HfOχNy/ HfO2/HfOχNy stack dielectric shows excellent electrical characteristics, such as field effect mobility of 10.2 cm2/V·s, on/off ratio of-106 and saturation current of 0.33 mA.