Role of high-k gate insulators for oxide thin film transistors

Abstract In conventional TFTs, SiO 2 or SiN x have been used as gate insulators. But they could not induce the high on-current due to their low-capacitance. Since they have low-capacitance that originated from low dielectric constant, on-current of TFTs with low-k insulated are limited by low-capacitance. We have investigated high- k materials, such as HfO 2 , ZrO 2 and modified structures for the use of gate insulators in oxide thin film transistors. ZrO 2 and HfO 2 are the most attractive materials with their superior properties, such as high breakdown field intensity (~ 15 MV/cm), high dielectric constant (~ 25), and the capability of room-temperature process. Since they have high-capacitance due to high dielectric constant, it can be easily expected to result in high on-current. In this work, we demonstrated the comparison of oxide thin film transistors with HfO 2 , ZrO 2 and SiO 2 and the roles of gate insulators are analyzed. In the result, oxide thin film transistors with SiO 2 , HfO 2 and ZrO 2 have on-currents of ~100 μA, ~500 μA, and ~3 mA, respectively. Especially oxide thin film transistor with ZrO 2 has larger on-current than oxide thin film transistor with HfO 2 . The result means that ZrO 2 is more suitable than HfO 2 for the gate-dielectric material which can be fabricated at room temperature.