In this letter, the unique reproducible nonpolar resistive switching behavior is reported in the Cu-doped ZrO ₂ memory devices. The devices are with the sandwiched structure of Cu/ZrO ₂ :Cu/Pt. The switching between high resistance state (OFF-state) and low resistance state (ON-state) does not depend on the polarity of the applied voltage bias and can be achieved under both voltage sweeping and voltage pulse. The ratio between the high and low resistance is on the order of 10 ⁶ . Set and Reset operation in voltage pulse mode can be as fast as 50 and 100 ns, respectively. No data loss is found upon continuous readout for more than 10 ⁴ s. Multilevel storage is considered feasible due to the dependence of ON-state resistance on Set compliance current. The switching mechanism is believed to be related with the formation and rupture of conducting filamentary paths.

The $\mathrm{Au}∕\mathrm{Cr}∕{\mathrm{Zr}}^{+}$ -implanted-$\mathrm{Zr}{\mathrm{O}}_2∕n^{+}\text{-}\mathrm{Si}$ sandwiched structure exhibits reversible bipolar resistive switching behavior under dc sweeping voltage. The resistance ratio $\left(R_{\text{ratio}}\right)$ of high resistive state and low resistive state is as large as five orders of magnitude with $0.5\mathrm{V}$ readout bias. ${\mathrm{Zr}}^{+}$ -implanted-$\mathrm{Zr}{\mathrm{O}}_2$ films exhibit good retention characteristics and high device yield. The impact of implanted ${\mathrm{Zr}}^{+}$ ions on resistive switching performances is investigated. Resistive switching of the fabricated structures is explained by trap-controlled space charge limited current conduction.

We use convincing experimental evidences to demonstrate that the nonpolar resistive switching phenomenon observed in $\text{Cu}/{\text{ZrO}}_2:\text{Cu}/\text{Pt}$ memory devices conforms to a filament formation and annihilation mechanism. Temperature-dependent switching characteristics show that a metallic filamentary channel is responsible for the low resistance state (ON state). Further analysis reveals that the physical origin of this metallic filament is the nanoscale Cu conductive bridge. On this basis, we propose that the set process (switching from OFF state to ON state) and the reset process (switching from ON to OFF state) stem from the electrochemical reactions in the filament, in which a thermal effect is greatly involved.

Resistive switching characteristics of ZrO2 films containing gold nanocrystals (nc-Au) are investigated for nonvolatile memory applications. The sandwiched top electrode/ZrO2 (with nc-Au embedded)/n+ Si structure exhibits two stable resistance states (high-resistance state and low-resistance state). By applying proper voltage bias, resistive switching from one state to the other state can be achieved. This resistive switching behavior is reproducible and the ratio between the high and low resistances can be as high as two orders. The intentionally introduced nc-Au in ZrO2 films can improve the device yield greatly. ZrO2 films with gold nanocrystals embedded are promising to be used in the nonvolatile resistive switching memory devices.

The resistive random access memory (ReRAM) device with three distinguishable resistance states is fabricated by doping Cu into a portion of the ${\text{ZrO}}_2$ oxide layer of the $\text{Ti}/{\text{ZrO}}_2/n^{+}\text{-}\text{Si}$ structure. The temperature-dependent measurement results demonstrate that filaments due to ionic trap-controlled space charge limited current conduction and metallic bridge are formed at different voltages. The formation and rupture of these different conducting filamentary paths in parallel are suggested to be responsible for the multilevel switching with the large resistance ratio, which can be used to establish a reliable multilevel ReRAM solution with variation tolerance.