Low-temperature (150 °C) processed metal-semiconductor field-effect transistor with a hydrogenated In–Ga–Zn–O stacked channel

Abstract

We developed low-temperature (150 °C) processed top-gate and coplanar metal-semiconductor field-effect transistors (MES-FETs) with a stacked In–Ga–Zn–O (IGZO) channel consisting of a hydrogenated IGZO (IGZO:H) on conventional IGZO (IGZO). The IGZO and IGZO:H films were prepared by Ar + O2 and Ar + O2 + H2 sputtering, respectively. By applying an IGZO:H on IGZO (IGZO:H/IGZO) stacked channel, the on-current of the MES-FET significantly increased while maintaining a low off-current. An on–off current ratio of 4.2 × 108, a turn-on voltage of −5.9 V and a subthreshold swing of 155 mV decade−1 were achieved by the IGZO:H/IGZO = 25/25 nm stacked channel. The carrier concentration of the IGZO:H/IGZO stacked film dramatically increased to 1.4 × 1019 cm−3 by stacking the IGZO:H (4.4 × 1017 cm−3) film on the IGZO (7.6 × 1017 cm−3) film. It was suggested that diffused hydrogens from IGZO:H to IGZO enhanced carrier concentration in the IGZO near the IGZO:H/IGZO interface, which acts as a pseudo two dimensional electron gas. Moreover, a potential barrier was formed at the IGZO:H/IGZO interface, which could have helped to maintain the low off-current of the MES-FETs. Therefore, the IGZO:H/IGZO stacked channel plays an important role in improving the performance of the MES-FETs.