Multi-Functional Bipolar Resistive Switching Originated from Self-Compliance Electroforming in Pt/WO3/Pt Memristive Devices
Authors: Tan Zheng-Hua , Yang Rui , Yin Xue-Bing , Guo Xin 
Published: February 2020

Memristive devices have great potential for the next generation of non-volatile memories due to their structural simplicity, high density, low cost, fast write-and-read access, and low-energy operation.1 In addition, memristive devices are also very promising for the neuromorphic computation as the basic building block with their ability to mimic synaptic plasticity such as short-term potentiation (STP), long-term potentiation (LTP), long-term depression (LTD), spike-timing-dependent plasticity and so on.2 The realization in one nano-device with both memory and neuromorphic properties will enable circuit fabrication using fewer elements with a smaller chip real estate.3 Generally, an electroforming process is necessary for the resistive switching (RS) performance,1where the soft breakdown happens with a compliance current (CC).
In this work, we report a multi-functional bipolar resistive switching (BRS) originated from self-compliance electroforming in Pt/WO3/Pt memristive devices by proper electrical operation, namely, an irregular multi-resistance storage with stable retention from polarity-reversible BRS and neuromorphic property from the other BRS resulting from Schottky-like barrier modulation. During the electroforming process, it was found that almost the same resistance value was obtained with different CC even in the case of no CC applied as shown in Figure 1(a) and (b). Subsequently, a proper positive voltage stimulus increased the resistance of memristive device as shown in Figure 1(c). Interestingly, the different resistance change could happen with the following applied negative voltage stimulus, resulting in different BRS. When the negative voltage was large enough, i. e., the curve 4 marked by blue as shown in Figure 1(c), the current would increase with a current jump and a counterclockwise BRS in the current-voltage curve occurred due to the filament generation and rupture. While the negative voltage was relatively small, i. e., the curve 4’ marked by red, the current decreased instead and a clockwise BRS happened, which should be ascribed to a carrier trapping and detrapping of the trap sites. These two kind of BRS were reversible with opposite voltage polarity. Thus, multi-resistance storage was realized which was irregular to the common reported one,4 where information could be safe due to its irregular operation. Again, after electroforming, if a relatively large voltage stimulus was applied, the resistance of memristive devices would increase to a higher level which was a low resistance state in the subsequent BRS as shown in Figure 1(d). A following negative voltage stimulus could reset the device while another positive stimulus could set such memristive device, which was similar with the reported BRS due to Schottky-like barrier modulation.2,3,5 Such a BRS exhibited a similar neuromorphic property, i. e., synaptic plasticity of continuous LTP with early-form LTP and late-form LTP, and LTD,2,6 which is the base of other forms of neuromorphic functions.
Figure 1. Electroforming resulting in almost the same resistance value with (a) different compliance current and (b) no compliance current applied. (c) The polarity-reversible BRS, and (d) another BRS resulting from Schottky-barrier like modulation following a relatively large voltage stimulus after electroforming.
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Figure 1