Roles Of Silver Oxide In The Bipolar Resistance Switching Devices With Silver Electrode And Direct Observation Of Local Resistance Switching In WO₃ Films

Electric-pulse-induced resistive switching (EPIR) phenomenon in metal/oxide/metal structure has recently attracted intensive attention due to its potential application in resistance random access memory (RRAM), a technique for the next generation nonvolatile memory.Three devices, Ag/WO_3-x/Pt (AWP), Ag/AgOx_/Pt (AOP), and Ag/AgO_x/WO-(3-x)/Pt (AOWP), were investigated to elucidate the influence of the silver oxide on the bipolar resistive switching behavior. The silver oxide films were obtained by depositing silver at oxygen atmosphere. We find that the resistive switching behavior was determined by the silver oxide layer. The three devices exhibit different I-V character, The AWP device exhibits a good linear Ohmic behavior with a resistance of ⁴0 . This is caused by the nonstoichiometry of the asdeposited WO_3-xfilm, where much oxygen vacancies exist resulting in a metalliclike transport property of the film. Bulk and interface resistive switching were observed in the AOP and AOWP devices, respectively. The I-V curves of the AOWP device exhibit not only a pronounced I-V hysteresis but also an obvious rectifying behavior. Comparing the I-V curves with the AWP and AOP devices, the rectifying property of the AOWP should be originated from the barrier at the AgO_x/WO_3-xinterface. We investigated the relationship between resistance and voltage or current, we found that there is a reasonable correspondence between resistance and voltage, whereas no clear relationship between resistance and current. Thus these results highlight that the bipolar resistance switching in present devices is induced by the electric field rather than the current. The micro-x-ray photoemission spectroscopy analysis demonstrated that the electrochemical redox reaction occurred in the AgO_x layer is responsible for the resistive switching behavior at silver/oxide interface. The resistance switching triggered by electric pulses was studied. The resistance of the AOWP device oscillates between the low resistance state (LRS) and the high resistance state (HRS) under the impact of alternative electric pulses of -1 V and +0.7 V (pulse width=1 s). The device shows more than 8000 cycles high-to-low resistance switching. The resistance switching ratio (R_OFF/R_ON) is about 20 and the retention property of the resistance state at the room temperature is at least 10000 s. Local resistance switching in WO₃films has been studied based on the conducting Atomic Force Microscope technique. Special attention was paid to the formation/reproducibility of local conduction regions on the metal-oxide interface for repeated setting-resetting operations and the effects of microscopic inhomogeneity. It is found that most of the conducting spot prefer to stay where they were once formed. However, only minority of them (³0%) are repeatable in resistance values for the writing-erasing cycling. According to the resistance switching behaviors, totally five kinds of locations can be classified, and they are inactive regions, weak transition regions, weak to stable transition regions, stable transition regions, and irregular transition regions. A further analysis shows the preferential locations of conduction spots at protuberant grains.