Heterojunction oxide thin-film transistors

Metal oxide (MO) semiconductors are an important class of materials for a large range of (opto)electronic applications, including as active channel material in thinfilm transistors (TFTs) for display technologies. Research effort in this field focuses on the improvement of device characteristics, with one of the main figures of merit being the electron mobility, as well as the stability against bias stress. While TFTs with a single layer MO as the channel material are limited by the inherent bulk properties of that MO, using heterojunctions (HJs) of bilayer or multilayer stacks instead offers ways to overcome those limitations. For example, interface effects such as the formation of a two-dimensional electron gas, can enhance the mobility beyond that of the single material components of the HJ. On the other hand, the combination of two layers with distinct functionalities (e.g. high mobility of material 1 with high stability and low off-currents for material 2) gives rise to well-balanced overall device characteristics that would not be achievable with either MO by itself. This chapter gives an overview of the materials, mechanisms and improvements involved with heterojunction metal oxide TFTs