Study On Solution-Processed Dielectric And Channel Layer For The Oxide Thin-Film Transistor

Amorphous oxide semiconductor thin film transistors (AOS-TFTs) is expected to substitute the conventional silicon based device for novel display technoloty due to their high mobility, high transparency in visible region and uniformity in large area. Many research work for preparing the oxide channel layers and dielectric layers are focused on vacuum technoloty such as sputtering, chemical vapor deposition, pulsed laser deposition and atomic layer deposition. But more and more attentions are paid to solution process for its simplicity, easy to control the chemical content, being apt for mass production and low cost. In this work, solution processed alumina dielectric layers and a-IZO channel layers are investigated. The main research contents and results are as follows:To overcome the low reactivity and unstability, the [Al(C4H9O)3] as precusor is used to prepare the alumina thin films by spin coating method. For comparison, poly 4-vinylphenol (PVP) is also prepared as dielectric layers. The MIM (aluminum dielectric layer-aluminum) measurement reveals that the leakage current density of the alumina layers is much better than that of the PVP layer, only 3×10-A/cm2 at 1 MV/cm, showing the excellent insulator property.Thin-film transistors with indium zinc oxide as the channel layer and alumina or PVP as dielectric layer were prepared. The device performance shows that solution processed alumina layer meet the requirement of oxide TFTs, indicating the possibility to be used as dielectric layers. The influence of different thickness of alumina layer and annealing temperature on the performance of the TFTs were investigated. When annealed at 450℃ for 140 nm thick alumina layer, The TFTs with optimized performance of threshold voltage of 2.2 V, current on/off ratio of 105, and saturation mobility of 1.4 cm2V-1S-1 is obtained.Amorphous IZO channel layers prepared by spin coating show good surface smoothness. The average transmission in visible light region is over 85%. The effect of In/Zn ratio in the solution, different annealing temperature and molybdenum doping on the TFTs performance were investigated. a-IZMO-TFTs with mobility of 1.75 cm2/Vs, current on/off ratio of 104, threshold voltage of-0.89 V and subthreshold value of 2.5 V/dec is obtained, confirmed the possibility for a-IZMO as the channel layers.Tungsten doped indium oxide thin films are prepared by pulsed plasma deposition. The optimized property with resistivity of 2.75 x 10-4 ohm-cm, carrier mobility of 53 cm2V-1s-1, and transmission of larger than 80% in visible region is obtained. The IWO thin films can be used as transparent electrodes for totally transparent oxide-TFTs.