ZnSnO 기반 박막트랜지스터의 전기적 특성에 관한 연구

Abstract

Amorphous oxide semiconductors have been regarded as promising alternatives materials for conventional a-Si and poly-Si in thin film transistors. Oxide-TFTs have lots of advantages, such as low temperature processing, transparency and high field-effect mobility. Many oxide semiconductors have been researched for applications such as active-matrix liquid crystal displays (AMLCDs) and flexible displays. Also, the transparent characteristics of oxide-TFTs have been intensively studied to be used in alternative active-matrix back planes for next generation flat panel displays. In particular, zinc-tin oxide (ZnSnO) has several advantages when used as material for the channel layer of oxide TFTs. In previous study, ZnSnO thin films have shown to be promising for application as an alternative transparent conducting oxide material due to cost efficiency and good thermal stabilities under the low pressure. For the improved electrical performance of ZnSnO TFTs, understanding of the electrical characteristics of Zinc-tin oxide material must be developed prior to their integration into electronic devices. In particular, there should be the proper deposition conditions when the ZnSnO TFTs are fabricated. There are also some issues related to the stability and contact resistance of ZnSnO TFTs, therefore, the fabrication of highly stable ZnSnO TFTs and low contact resistance of ZnSnO TFTs should be investigated. The goal of this thesis is the fabrication TFT devices having the ZnSnO channel layer and the improvement of electrical characteristics of properly optimized ZnSnO TFTs. This thesis contains the first detailed electrical characterization study of ZnSnO TFTs, the improved electrical stability by Hf doping on zinc-tin oxide TFTs and the investigation of effective contact resistance of ZnSnO TFTs with various S/D electrode materials. The most important achievement contained herein is the optimization of fabrication process when ZnSnO is used as the channel layer of TFTs to get the improved electrical characteristics and stability. According to results, when zinc-tin oxide is used in TFTs as an active channel layer, the fabrication process could be optimized that annealing temperature of 400 ℃ for an hour and oxygen partial pressure of 10% is most proper to use in device. Also, based on that condition, the most issued problems in oxide TFTs, instability problem could be solved by doping 1.0 at.% of hafnium on ZnSnO channel layer. And the results showed that Hf doping could effectively enhance the stability of ZnSnO TFTs with optimized experimental conditions. And by comparing the contact resistance between ZnSnO channel layer and various S/D electrodes, the most proper electrode for ZnSnO TFTs could be selected as Mo which has the lowest work function forming ohmic contac with ZnSnO thin film. As a result of this thesis, the ZnSnO TFTs fabricated in optimized conditions having good electrical characteristics and stability could be highly considered as promising candidates for the next generation electronic devices.