Performance and Stability of ZnO/ZnMgO Hetero-Metal–Insulator–Semiconductor Field-Effect Transistors

Abstract

We studied the structures of ZnO/ZnMgO heterostructure field-effect transistors (FETs) to achieve high performance and stability in these devices. Two types of heterostructure were examined. One consisted of a ZnO channel layer and a thin ZnMgO cap layer to form a hetero-metal–insulator–semiconductor (hetero-MIS) structure, and the other had formed a conventional MIS structure. Both Al2O3 and HfO2 were examined as high-k gate dielectrics. The results indicate that high-performance FETs can be obtained using a hetero-MIS structure and that the reduction in access resistance is crucial for further improvements in FET performance. In addition, both an increase in transconductance and a stable FET operation were realized for the hetero-MIS structure by replacing the Al2O3 gate dielectric with a HfO2 gate dielectric. Stable operation was verified from the observation of a markedly reduced hysteresis less than 0.1 V for HfO2, which was lower than that for Al2O3.