Thus, filament formation is determined by the intrinsic ReRAM characteristics without any influence of the tunnel barrier. An additional filament can be formed along the partially formed filament for achieving set operation of the LRS because most of the electric field and current focus on the partially formed conductive filament path (Figure 5d). Consequently, the tunnel-barrier-integrated ReRAM can exhibit higher switching uniformity than a control sample without a tunnel barrier. Furthermore, the selected LRS and HRS and unselected LRS switching find more current uniformity were more reliable with the higher selectivity of the ReRAM, which has the multi-layer TiOy/TiOx, than with the lower selectivity of the ReRAM (Figure 6a,b,c).

We confirmed that resistive switching uniformity can be improved by a tunnel barrier of high selectivity. In the case of higher selectivity, the RDT value is higher and more effectively controls the current flow of the ReRAM for uniform small filament formation. The smaller filament formation with higher selectivity was confirmed by the lower reset current (IReset), as shown in Figure 6d. In general, IReset is related to filament size, and a larger filament requires a higher IReset. It is well known that the filament size is determined at the set operation, and

the filament size determines IReset [16, 17]. Thus, a higher selectivity of the ReRAM leads to a lower IReset with smaller filament formation by tunnel selleck chemical barrier controlled current flow. Figure 6 Switching current distributions (a, b, c) and relationship P-type ATPase between selectivity values and I Reset (d). (a, b, c) Switching current distributions with various tunnel barriers with various

selectivity values (selectivity of blue, red, and black are 66, 38, and 21, respectively). (d) Relationship between selectivity values and IReset. Finally, the reliability of non-volatile memory applications was evaluated. To measure endurance, we applied a 1-μs pulse width of +2 V/-2.2 V (Figure 7a). It exhibited high endurance of up to 108 cycles (Figure 7b). Furthermore, we confirmed that the selector-less ReRAM suppressed leakage current in AC pulse operation. In a real cross-point array, pulse operation characteristics are highly important. In addition, retention was measured at 85°C for more than 104 s without noticeable degradation (Figure 7c). Figure 7 Pulse conditions (a), endurance reliability (b), and retention (c) measurement. Conclusion The role of a multi-functional tunnel barrier was investigated. The main concern areas of selectivity and switching uniformity were significantly improved. This is attributed to the tunnel barrier acting as an internal resistor that controls electron transfer owing to its variable resistance. In addition, the effect of the tunnel barrier on selectivity and switching uniformity was stronger in a multi-layer TiOy/TiOx than in a single-layer TiOx owing to the greater suppression of the VLow current flow.