Figure 2. Multilevel non-volatile resistive switching behavior and reliable potentiation/ depression.

(a) The device can be set by increasing the compliance current and it can be reset with negative voltage sweeps of increased amplitudes to different resistance levels. The red curve shows the IV characteristic without compliance current, and the blue curves indicate switching at different compliances. (b) Retention tests of 8 different levels at 150 °C (>10⁴ s), confirming nonvolatile behavior and indicating the device is suitable for multi-level memory. (c) A typical analog switching cycle in which the conductance can be gradually increased with 26 positive pulses (100 ns, 0.75 to 1 V, 10 mV step) (potentiation), and gradually decreased with 13 negative pulses (100 ns, −1.05 to −1.17 V, 10 mV step) (depression). (d) 2²⁰ potentiation/depression epochs, each consists of 39 pulses, have been achieved, suggesting that the device is also promising as electronic synapse for neuromorphic computing.