The Fabrication And Charateristics Of Vertical-Type ZnO Thin Film Transistor

Metal oxide thin film transistors (Oxide TFT) have many advantages such as, wide band gap, high uniformity, high stability, and high mobility of carriers compared with conventional silicon and organic semiconductor TFT, and Znic Oxide (ZnO) has attracted significant attention in the field of Oxide TFT because of its nontoxicity, low temperature fabrication process, high optical transparency in the visible range and abundance in nature resourece. In this paper, we first fabricated and analysis the feature of the ZnO thin film, and then fabricated the Schottky diode and vertical-type Ag/ZnO/Al/ZnO/Ag thin film transistor using ZnO as the active layer. The results are listed as follows:ZnO thin film was deposited on the quartz glass using Zn target (99.99%) by RF magnetron sputtering. The sputtering ZnO active layer was carried out in a mixed atmosphere of Ar and O2(99.99%) in the glow discharge progress. Using scanning electron microscope (SEM) and X-ray diffraction (XRD) to analysis ZnO thin films that deposited at different substrate temperature. Then we got the process parameters for a well C-axis orienation and the surface is clean and smooth.In the same conditions of depositing ZnO thin film, a Al/ZnO/Ag Schottky barrier diode detctor was designed and fabricated on the quartz glass substrate. The characteristics of dark-and 365 nm photo-current of the Schottky UV photodetector was investigated. The metal eletrode was fabricated by DC sputtering. We get the height of barrier which formed between Ag and ZnO is 0.53 eV, and the ideality factor is about 12.6. The space charge density is 3.13 x 1016 cm-3 and the barrier height is 0.6 eV that calculated by C-V curves. The obtained barrier height has a slight difference calculated by different theories, within the acceptable range. Good rectification coefficient 104) indicate that there is a good Schottky behavior between Ag and ZnO. The results which the device with 365 nm monochromatic light illumination indicate the diode has a strong aborption of ultraviolet light. The sensitive of the diode arrived at 0.335A/W. With the positive bias of 2 V and 3 V, photogenerated current arrived at 0.99 mA and 3.28mA respectively, suggest that Al/ZnO/Ag UV photodetector has a significantly light response characteristics.Finally, we have designed and fabricated vertical-type Ag/ZnO/Al/ZnO/Ag thin film transistor with ZnO as an active layer on glass substrate. The device has a short channel length and a fast switching speed. By illuminating its specific energy band structure, explain the tunneling mechannism. Compared with the conventional devices, the prepared one can obtain a high working current (-9.15×10-3 A) in a low driving voltage (-3 V) and the threshold voltage is only 1.35 V. We also calculate the transfer characteristics, transconductance, output resistance, the voltage amplification factor, and the carrier mobility and the ratio of Ion/Ioff. The results shows a little Ioy/Ioff(103). The carrier mobility of the active layer is 0.33cm2V-1s-1. While the device has a small output resistance and the voltage amplification factor.