Effects of Nb doping on switching-voltage stability of zinc oxide thin films

Nb-doped ZnO (NbxZn1-xO, NZO) thin films with various Nb additions (x = 0, 0.2, 0.5, and 0.8 at. %) were deposited on Pt/TiO2/SiO2/Si substrates by radio frequency magnetron sputtering. The Nb doping concentration was found to affect the microstructure, the number of oxygen vacancies, and work function of the Pt/NZO/Pt structures. Among the various devices, the film with 0.5 at. % Nb addition showed a better switching-voltage stability [i.e., the optimal coefficient of variation (Cv) for reset (7.02%) and set (2.73%) operations, respectively], a high endurance (∼1000 cycles), and lower reset (0.57 V) and set (1.83 V) voltages due to a larger number of oxygen vacancies and a lower work function. In general, the results show that the present NZO thin films are promising candidates for stable and low power-consumption resistive random access memory applications.