Electrical characteristics and stability of novel MgxZn1-xO (0 ≤ x ≤ 0.06) thin film transistors

Thin Film Transistor (TFT) is emerging for large area electronics and systems. TFT applications include displays, photovoltaics, sensors, smart labels, lighting, integrated logic devices, and embedded power sources. However, the conventional amorphous silicon (a-Si) TFTs, which have dominated display technologies as switch devices in control circuitry, are facing severe challenges due to its low electron mobility (≦1 cm2/V-s) and opacity. The advanced display systems demand the new TFT technology with low power consumption, high resolution, large area, and fast refresh rate. There has been increasing interest in the use of oxide-based TFTs as electronic back-plane switching devices for the next generation of large area flat-panel display applications. Zinc oxide (ZnO) has been receiving considerable attention as a promising oxide semiconductor for TFT technology for the future displays due to its higher electron mobility (~10-50 cm2/V-s), transparency in visible light region, and superior radiation hardness over the a-Si TFTs. To implement ZnO TFTs into novel display systems, stability of ZnO TFTs is the most critical issue and has to be examined. The aim of this dissertation research is to study and enhance electrical characteristics and stability of ZnO TFTs using the ternary MgxZn1-xO (0 ≤ x ≤ 0.06) as the TFT channel layer. The MgxZn1-xO (MZO) is grown by Metal Organic Chemical Vapor Deposition (MOCVD) through in-situ alloying of MgO and ZnO. Mg composition in the MgxZn1-xO is controlled below 6% (x ≤ 0.06) to avoid alloying disorder induced degradation. In the ternary compound MgxZn1-xO, the incorporation of Mg into ZnO along with stronger Mg-O bonding effectively suppresses the oxygen vacancy related defects and improves the electrical characteristics of ZnO-based TFTs. The lower subthreshod slope and higher field effect mobility are obtained in MZO TFTs. In addition, MZO TFTs technology exhibits superior thermal stability. Under a negative bias stress (NBS) testing, MZO TFTs show smaller negative shift of threshold voltages than that of the ZnO counterpart, owing to less ionization and migration of oxygen vacancies. The new MZO TFTs technology presents a great impact on the future classes of low cost and large area electronic applications, such as display systems, sensor arrays, and solar energy conversion.Ph. D.Includes bibliographical referencesby Chieh-Jen K