*Memristor - An Emerging Device for Post-Moore's Computing and Applications*

account of the reduced oxygen vacancy concentration at the other end [47]. It states that both the interfaces cannot switch simultaneously. One needs to switch OFF when the other is ON. The mechanism of CRS is explained in terms of the distribution of defect within the insulating i.e. switching layer. After the applied electrical bias (positive or negative), the movement of defects towards certain electrode is observed. Depending upon the accumulation of defects at one or opposite interface, the SET and RESET states occur giving current levels under +ve and/or -ve bias conditions. With the help of either current compliance condition or sudden stop of bias at current peaks, only the SET state is obtained and one can limit the RESET state to takes place giving rise to bipolar switching [48]. Compared to other resistive switching devices, CRS provides slow and steady SET operation at one interface rather than an abrupt transition in current level. At the same time, RESET operation occurring at other interface eliminates the need of positive feedback [49]. It is known that an individual VCM device can exhibit CRS operation. For VCM devices with symmetric stack and similar top and bottom metal electrodes shows CRS phenomenon (**Table 4**).


### **Table 4.** *Comparison for complementary type RS devices.*
