Fabrication And Properties Of Si-doped ZnO-based Thin-film Transistor With Dual-active-layer Structure

With the fast development of information technology, more requirements have been given to improve display technology. The active matrix liquid crystal displays(AMLCD) and active matrix organic light emitting diode display(AMOLED), as the representative of flat-panel display technology, has been also developing rapidly and occupying the mainstream of flat-panel display market. Thin film transistor is a key device as the switch and driving device of AMLCD and AMOLED, Zn O thin film transistor(Zn O-TFT) is considered to be the most promising next generation TFT technology, due to its high mobility, simple preparation technology and transparency in the visible range. But the electrical properties and stability of the Zn O-TFT need to be continually improved to satisfy an application requriements in the flat display technology. So it is very significant to investigate the doped, active layer structure and stability of Zn O-based TFT for promoting its developments and applications.In this work, the TFTs with Zn O and Si-doped Zn O(SZO) film as a single active layer structure and the TFT with SZO/Zn O acted as dual-active-layer(SZO/Zn O-TFT) were fabricated by magnetron sputtering method. Their electrical properties and stabilities were researched in detail. The main contents and results are as follows:(1) The effects of substrate temperature and silicon content on optical transmittance of SZO film and electrical properties of the SZO-TFT were investigated. The results indicate that, the optical transmittances of all the SZO films deposited at the substrate temperature from 100 ℃ to 250 ℃ are higher than 85% in the visible light region. Among these samples, the SZO-TFT for the substrate temperature of 150 ℃ shows the best comprehensive performance. The optical band gap of the SZO film increases with increasing Si content, and resulting in better optical transmittance in the visible light range. Appropriate si-doped content in the Zn O films can effectively reduce the off-state leakage of the SZO-TFT, and increase the on/off current ratio by more than two orders of magnitude, but the carrier mobility and the saturated leakage current decreases.(2) The electrical properties of Zn O-TFT, SZO-TFT and SZO/Zn O-TFT were investigated by comparesion. The results indicate that the SZO/Zn O dual-active-layer architecture used in the Zn O-based TFT could increase on/off current ratio by about two orders of magnitude with no reduction in carrier mobility, and thus optimize the performance of the device.(3) The effects of positive gate-bias and drain-bias stability of the Zn O-TFT, SZO-TFT and SZO/Zn O-TFT were investigated. The results indicate that the stability of the SZO/Zn O-TFT with dual-active-layer under the positive gate-bias and drain-bias stresses is improved obviously, which is attributed to the electronic barrier formed at SZO/Zn O interface and the reduce of oxygen vacancy in SZO film.(4) The air-stability of the Zn O-TFT and SZO/Zn O-TFT were investigated. The results indicate that, compared with the Zn O-TFT, the stability of the SZO/Zn O-TFT with dual-active-layer in the air environment is improved obviously. This is because the SZO film with more dense structure can prevent oxygen and water vapor into the Zn O film at the bottom of the channel layer, and thus suppress the back-channel effect.