Fabrication And Characteristics Analysis Of Thin Film Transistors With Tunneling Effect

As the core part of the thin-film transistors liquid crystal display (TFT-LCD) and active-matrix organic electroluminescent display, the research of thin-film transistors is the major investment and core technology of TFT-LCD and AM-OLED. Wherein the thin-film technology for TFT-LCD has been relatively mature and yield is relatively high. However, it isn’t for the thin-film technology of OLED due to the driven mode. The driven mode for OLED is current mode which is different from LCD. Then the requirement for the current and switching ratio is higher. We focus on the structure of the thin film transistors; thin film transistors with tunneling effect are prepared. The structure of transistor is vertical structure. The channel of thin film transistor is reduced mostly. The characteristics of transistors are developed.Firstly. ZnO thin film was prepared by magnetron sputtering Zn target and reacting with oxygen on the glass substrate. The thin film structure was analyzed by X-ray diffraction at different temperatures. Process parameters with good C-axis orientation and flat surface were confirmed.Then, thin film transistors with tunneling effect were prepared, and zinc oxide is semiconductor layer. The structure of transistors was a sandwich structure of Ag/ZnO/Al/ZnO/Ag. Ag and Al layers as the electrodes were prepared by DC magnetron and ZnO were prepared by magnetron sputtering. Schottky contacts were formed between Ag and ZnO; and ohmic contact between Al and ZnO. The zinc oxide transistors which prepared at different times and temperatures were tested by semiconductor tester. The operating current was up to degrade of mA. The transistor prepared at 200℃ was best. The increase of sputtering time can promote the formation of Schottky barrier at the cost of increase of channel length. The driven voltage increased and the current reduced. The height of Schottky barrier is 0.68eV and 0.56eV which is calculated by capacitance-voltage and current-voltage. respectively. And the carrier concentration is about 3.231×1015cm-3.Finally, the characteristics of thin film transistors were analyzed by basic electrical characteristics. The parameters which represent the characteristics of thin film transistors were calculated such as transistor transconductance, output resistance and voltage amplification factor and so on. It can be obtained that the carrier mobility is about 0.1509cm2/Vs. The threshold voltage is about 0.5V which is smaller than horizontal structure. The working mechanism of tunneling effect thin film transistors was analyzed by using the carrier transport mechanism of metal-semiconductor contact. The result showed that the carriers of thin film transistor are electrons. The electrons meet the Fowler-Nordheim tunneling effect theory and injected into the semiconductor layer from the Ag electrode.