High mobility InGaZnO thin film transistor using narrow-bandgap titanium-oxide semiconductor as channel capping layer

Metal-oxide InGaZnO thin-film transistors (IGZO TFTs) have received substantial attention as potential substitutes for amorphous Si and/or polycrystalline Si in active-matrix liquid-crystal displays, active-matrix organic light emitted diodes (AMOLEDs), and three-dimensional (3D) display applications [1]-[2]. It is well known that the multi-alloy IGZO channel plays an important role in device characteristics such as subthreshold swing (SS) and field-effect mobility (μ_FE). Although the high-K gate dielectrics to lower operating voltage and threshold voltage (V_T) of TFT devices have demonstrated [3]-[5], these critical issues on transfer characteristics still need to be overcome. The large SS and low μ_FE prevent them from being applied in fast-switching and high-resolution displays. In this paper, we demonstrate high mobility IGZO TFT with titanium oxide (TiO_x) channel capping layer. Large μ_fe of 66 cm²/Vs and low SS of 79 mV/dec were achieved using narrow-bandgap TiO_x (E_g~ 3.1eV) [6] with optimized 5-nm thickness. The similar bandgap and conduction band offset to those of IGZO are favorable to obtain a low resistance ohmic contact between amorphous IGZO and Al contact metals.