ZrS2 symmetrical-ambipolar FETs with near-midgap TiN film for both top-gate electrode and Schottky-barrier contact

ZrS2 amibipolar MISFETs are obtained in operations with both electrons and holes. A layered polycrystalline ZrS2 thin film was formed by sputtering and sulfur-vapor annealing on a whole surface of a 2.4 cm × 2.4 cm SiO2/Si substrate. The ZrS2 FETs have Al2O3 gate insulator and TiN film for both the top-gate electrode and Schottky-barrier contact, which show symmetrical Id-Vgs curves with a Voff of 0.4 V contributed by the TiN film with midgap work function to the sputtered ZrS2 film. Notably, ambipolar FET operations because of both electrons and holes were successfully observed with an on/off current ratio of 250. This is an important step to realize n/p-type unipolar ZrS2 FETs.