Effect of stoichiometry on the resistive switching characteristics of STO resistive memory

Abstract

Herein, SrTiO₃ (STO) resistive memories with write-once-read-many-times (WORM) function were fabricated. The STO resistive switching (RS) layers were deposited at a sputtering power in the range of 40–120 W and oxygen flow rate in the range of 0–3 sccm. Without the addition of oxygen, the deposited STO films were non-stoichiometric, and the Sr/Ti ratios were all higher than unity. The ON/OFF current ratio of the STO memory deposited at 40 W was 10⁶. When the power increased from 40 W to 120 W, a decrease in the Sr/Ti ratio was obtained. The stoichiometry of the STO film was closer to unity. Moreover, the memory showed a higher ON/OFF current ratio of 5 × 10⁶. Oxygen was further introduced during the sputtering process to adjust the STO stoichiometry. The Sr/Ti ratio decreased from 1.54 to 1.04 when STO was deposited at an oxygen flow rate of 1 sccm. The stoichiometric STO RS layer resulted in a significantly higher ON/OFF current ratio of 2 × 10⁸. The STO film became nonstoichiometric, where the Sr/Ti ratio was lower than unity when the oxygen flow rate further increased to 3 sccm. The data storage capability of the STO memory was investigated. Moreover, stability tests were performed at 85 °C to study the lifetime of the device. Temperature-dependent measurement was performed to verify the validity of the filamentary mechanism. Also, the carrier conduction mechanism and energy band diagram were studied and illustrated.