Fig. 3 (a) PPF function under a pair of positive pulses (5.5 V, 10 ms). (b) short-term plasticity after removing the operating pulse.
Pair-pulse facilitation (PPF) is an important short-term synaptic function involved in several neuronal tasks, such as reinforcement learning and information filtering [7]. Fig. 3a shows the experimental demonstration of PPF function in the proposed Pt/HZO/TiN device. When a pair of pulses (5.5 V, 10 ms) was applied to the device, the response current gradually increased during the positive bias, and the maximum response current of the second pulse was clearly larger than the first one. But the current at the beginning of the second pulse is obviously smaller than that at the ending of the first pulse, which means a decay during the pulse interval. Fig. 3b further shows the short-term plasticity of the self-rectifying device. After removing the operation pulse (5.5 V, 10 ms), the device state can be maintained for about 7 ms, monitoring by the 3 V bias voltage. Thus, the short-term plasticity can also also be realized in Pt/HZO/TiN device.