Performance and stability of ZnO/ZnMgO hetero-metal-insulator-semiconductor field-effect transistors

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 Al(2)O(3) and HfO(2) 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 Al(2)O(3) gate dielectric with a HfO(2) gate dielectric. Stable operation was verified from the observation of a markedly reduced hysteresis less than 0.1 V for HfO(2), which was lower than that for Al(2)O(3).