Institute of Materials in Electrical Engineering and Information Technology II (IWE2), RWTH Aachen University, 52056 Aachen, Germany.
Nanoscale. 2017 Oct 5;9(38):14414-14422. doi: 10.1039/c7nr04896c.
Current-voltage characteristics of oxide-based resistive switching memories often show a pronounced asymmetry with respect to the voltage polarity in the high resistive state (HRS), where the HRS after the RESET is more conducting than the one before the SET. Here, we report that most of this HRS asymmetry is a volatile effect as the HRS obtained from a read operation differs from the one taken from the switching cycle at identical polarity and voltages. Transitions between the relaxed and the volatile excited states can be achieved via voltage sweeps, which are named subloops. The excited states are stable over time as long as a voltage is applied to the device and have a higher conductance than the stable relaxed state. Experimental data on the time and voltage dependence of the excitation and decay are presented for Ta/TaO/Pt and Ta/ZrO/Pt devices. The effect is not limited to one oxide or electrode material but is observed with different magnitudes (up to 10× current change) in several oxide systems. These observations describe an additional state variable of the memristive system that is controlled in a highly polarity dependent manner.
基于氧化物的电阻式随机存取存储器的电流-电压特性通常表现出对高阻状态（HRS）中电压极性的显著不对称性，其中重置后的 HRS 比置位前的 HRS 更具导电性。在这里，我们报告说，这种 HRS 不对称性大部分是一种易失性效应，因为从读取操作获得的 HRS 与在相同极性和电压下从开关周期获得的 HRS 不同。通过电压扫描（称为子循环）可以实现弛豫态和易失态激发态之间的转换。只要向器件施加电压，激发态就会保持稳定，并且具有比稳定弛豫态更高的电导率。给出了 Ta/TaO/Pt 和 Ta/ZrO/Pt 器件上激励和衰减的时间和电压依赖性的实验数据。该效应不仅限于一种氧化物或电极材料，而是在几种氧化物系统中以不同的幅度（高达 10 倍电流变化）观察到。这些观察结果描述了忆阻系统的另一个状态变量，该变量以高度依赖极性的方式进行控制。
