Study Of Oxide Electronic Materials And Applications In Thin Film Transistors

The active matrix liquid crystal display (AMLCD) is mainly used in hydrogenated amorphous silicon thin film transistor (a-Si:H TFTs) as pixel switch panel. a-Si:H TFTs-LCD limits its further development in the liquid crystal display because of its opacity, low mobility and threshold voltage drift. Oxide electronics is a very diverse and active field, including materials such as dielectrics, ferroelectrics, magnetics, piezo-electrics, multiferroics, high-temperature superconductors, epitaxial oxides, memories, and sensors. Oxide thin-film transistors can be further subcategorized by specifying whether the structure of the TFT channel layer is amorphous, monocrystalline or polycrystalline. Amorphous oxide semiconductors (AOS) TFTs can replace the s a-Si:H TFTs due to its high mobility, high transmittance and low temperature compatible process. Amorphous materials are more readily and economically scaled to the exceedingly large dimensions required for active matrix liquid crystal display (AMLCD) high-volume manufacturing. We confine our attention to a specific class of amorphous channel layer materials-AOS TFTs. The main work of the dissertation are as follows:1. The effect of growth temperature and annealing on the physical properties of Zn3Sn2O7 (ZTO) thin films was investigated in this paper. The ZTO thin films were deposited on glass substrates by rf magnetron sputtering. It is found that the films are amorphous regardless of the growth temperature. The film grown at room temperature shows the highest mobility of 8.1 cm2·V-1·s-1 and the lowest carrier concentration of 2.0×1015cm-3. The highest carrier concentration of 1.6×1019 cm-3 is obtained at the growth temperature of 250℃. Annealing treatment of the ZTO thin films resulted in the increases of carrier concentration and mobility. By using a ZTO thin film as the channel and a Ta2O5 thin film as the insulating layer, we fabricated transparent ZTO thin film transistors with the field effect mobility of 24.76 cm2·V-1·s-1, the threshold voltage of 1.2 V. On this basis, using focused ion beam(FIB) technique, ZTO nanowire transistors were prepared.2. This work on the fabrication and characterization of transparent amorphous zinc tin oxide (a-ZTO) thin-film transistors using an 80nm thick ZTO film as an active layer on a 50nm thick Al2O3 gate dielectric film grown by atomic layer deposition. The Al2O3/a-ZTO thin-film transistors achieve low-voltage operation with a saturation mobility of 1 cm2·V-1·s-1, excellent subthreshold slope of 0.2 V/dec, a threshold voltage of 3.1 V, and on/off current ratio of 106 (W/L= 200μm/10μm) at 4 V. The contact resistance is found the same degree as the total resistance. The overall contact resistance of a-ZTO TFTs may be much more affected by the intrinsic property of the semiconductor, rather than the interface of electrode and channel Improve the quality of the amorphous semiconductor materials can reduce the contact resistance of TFT device, so as to improve the performance of electronic devices3. Study of nickel oxide (NiO) film as the active layer of p type thin film transistor. The influence of growth temperature and 02/Ar flow ratio on the structural and electrical properties of a-NiO thin films has been systematically investigated. Electrical measurements have indicated the decrease in resistivity at higher 02/Ar gas flow ratio. Pure Ar ambient with room temperature growth of NiO films shows the highest mobility of 1.07 cm2/V·s, and hole concentration of 2.78×1017 cm-2. Initial p-type NiO-based thin film transistors grown by magnetron sputtering demonstrated a mobility of 0.05 cm2·V-1·s-1, a threshold voltage of -3V, subthreshold swing of 2.6 V/dec, the current on-off ratio of 103, respectively.