Reactive sputtering of substoichiometric Ta₂O_x for resistive memory applications

A major class of resistive memory devices is based on transition metal oxides, where mobile oxygen vacancies allow these devices to exhibit multiple resistance states. Ta₂O₅ based devices in particular have recently demonstrated impressive endurance and forming-free results. Deposition of substoichiometric Ta₂O_x (x < 5) films is a critical process in order to produce the required oxygen vacancies in these devices. This paper describes a physical vapor deposition (PVD) reactive sputtering process to deposit substoichiometric Ta₂O_x films. The desired film stoichiometry is achieved by feedback control of the oxygen partial pressure in the PVD chamber. A calibration procedure based on Rutherford backscattering spectroscopy is described for locating the optimum oxygen partial pressure.