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This study investigates an improvement in memory characteristics through depositing an In2O3 layer as an oxygen ion reservoir in the switching layer (SL) of resistive random access memory (RRAM). The deposition of In2O3, denoted as Pt/HfO2/In2O3/TiN device, provides better memory characteristics including lower forming voltage (VF), set/reset voltage (VSET/VRESET), larger memory window, and higher resistances with higher uniformity at low resistance state (LRS) and high resistance state (HRS), compared to the devices without the In2O3 deposition, denoted as Pt/HfO2/TiN device. The conduction mechanisms, verified through fitting current–voltage (I - V) curves, are consistent with the results of a varied temperature I - V experiment. Finally, a physical model is proposed to explain our observations. [ABSTRACT FROM AUTHOR]

In this paper, vanadium oxide (VOx) was chosen for the resistive switching layer in a typical resistive random access memory (RRAM) structure. During negative forming bias, we found an initial selector property. This indicates the presence of metal–insulator-transition characteristics in the VOx layer even without an annealing process. In order to study this phenomenon, material analyses were conducted, with results indicating that there are V-O stretching bonds and an oxide/vanadium ratio of nearly 2.2 (${O}/{V} = {2.2}$). In addition, the experimental results of the dc sweeping test indicated that off-state current gradually decreased after each cycle, meaning that the selectivity characteristics in the VOx selector could be improved. Endurance performance of our experimental devices reached 108, sufficient for integration with RRAM devices in a 1S1R array. To further investigate this special phenomenon, current fitting analysis and simulation analyses were conducted. The results of the fitting analysis indicated that the conduction mechanism for off-state current was Schottky emission and the Schottky distance increased with increasing numbers of cycles. In other words, oxide ions migrate toward the filament at low negative voltage during dc sweeping, causing the formation of VOx. Furthermore, the results of thermal field simulation analysis indicated that there is a thermal concentration effect in and around the filament. Thus, oxide ions more easily migrate toward the vanadium filament when a stronger electrical field is present around the filament during dc sweeping cycles. Finally, stable vanadium selector characteristics are obtained and a conduction filament behavior model is proposed. [ABSTRACT FROM AUTHOR]

This letter introduces a method of using bipolarity bias voltages in the forming process to effectively reduce the forming voltage of a one-transistor and one-resistance random access memory device. A bipolar incremental-step-pulse programming process is applied, and a complete operation pulse for the forming process is described. This method reduces forming voltage without any cost to the device performance, and the device maintains good reliability. The likely physical mechanism of this bipolar operation is also presented based on the measured electrical characteristics. [ABSTRACT FROM PUBLISHER]