Effects of oxygen and moisture on the I-V characteristics of TiO2 thin films

Current-voltage (I-V) characteristics well reveal the resistive switching performance of materials promising for the next-generation memory-resistance random access memory (ReRAM). It has been observed that the atmospheric environment can affect the resistive switching performance, but the origin of this effect is still under debate. Conductive Atomic Force Microscopy (c-AFM) is widely used to study the resistive switching performance because of its capability to realize the resistive switching at the nanoscale that is becoming attractive as the miniaturization of memory devices. This study therefore aims to understand the effects of oxygen and moisture on the I-V characteristics of the TiO2 thin film by performing c-AFM measurements in ambient air, synthetic air, and argon gas. It is found that the oxygen in the environment can reduce the set and the reset voltages for the resistive switching, and it can also reduce the resistance at the low resistance state (LRS). Where the moisture in the environment can increase the set and reset voltages, and increase the resistance at LRS. These effects of oxygen and moisture in the environment can be attributed to the modification of the effective electric field during the resistive switching processes, which have been further confirmed by Kelvin Probe Force Microscopy (KPFM) measurements. In addition, it is found that the local ionic dynamics of TiO2 during the resistive switching are strongly dependent of the environments by performing the FORC-IV (First Order Reversal Curve-Current-Voltage) measurements in the three gas environments. Results in this work can provide a new perspective on the effect of environments on the resistive switching of materials, that is, the modulation of the effective electric field due to the adsorption of oxygen and moisture under the c-AFM tip. Keywords: Resistive switching, Environmental control, c-AFM, KPFM, FORC-IV