High-Performance Top-Gate Thin-Film Transistor with an Ultra-Thin Channel Layer

Metal-oxide thin-film transistors (TFTs) have been implanted for a display panel, but further mobility improvement is required for future applications. In this study, excellent performance was observed for top-gate coplanar binary SnO2 TFTs, with a high field-effect mobility (mu(FE)) of 136 cm(2)/Vs, a large on-current/off-current (I-ON/I-OFF) of 1.5 x 10(8), and steep subthreshold slopes of 108 mV/dec. Here, mu(FE) represents the maximum among the top-gate TFTs made on an amorphous SiO2 substrate, with a maximum process temperature of <= 400 degrees C. In contrast to a bottom-gate device, a top-gate device is the standard structure for monolithic integrated circuits (ICs). Such a superb device integrity was achieved by using an ultra-thin SnO2 channel layer of 4.5 nm and an HfO2 gate dielectric with a 3 nm SiO2 interfacial layer between the SnO2 and HfO2. The inserted SiO2 layer is crucial for decreasing the charged defect scattering in the HfO2 and HfO2/SnO2 interfaces to increase the mobility. Such high mu(FE), large I-ON, and low I-OFF top-gate SnO2 devices with a coplanar structure are important for display, dynamic random-access memory, and monolithic three-dimensional ICs.