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 (µ_FE) of 136 cm²/Vs, a large on-current/off-current (I_ON/I_OFF) of 1.5 × 10⁸, and steep subthreshold slopes of 108 mV/dec. Here, µ_FE represents the maximum among the top-gate TFTs made on an amorphous SiO₂ substrate, with a maximum process temperature of ≤ 400^◦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 µ_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.