Realizing Bidirectional Threshold Switching in Ag/Ta2O5/Pt Diffusive Devices for Selector Applications

Abstract

Memristor crossbar arrays have great potential in brain inspired computing and the next generation high-density memories. The sneak current issue, however, seriously degrades their performance with increasing array size. Selectors with volatile threshold switching (TS) behavior have become important components of the arrays to suppress this issue. Ag/Ta2O5/Pt diffusive devices have promising TS characteristics as selectors, including high ON/OFF ratio and low OFF current. However, their unidirectional TS excludes their application in arrays consisting of bipolar memristors. Bipolar memristors require voltage biases of different polarities to enable the device programming, thus selectors with bidirectional TS are essential for them. In this study, we realize reproducible bidirectional TS behavior on Ag/Ta2O5/Pt diffusive devices. The ON/OFF ratio and the OFF current of the device are ∼107 A and ∼ 10−12 A, respectively. The switching voltage is ∼ 0.35 V and the hold voltage is ∼ 0.125 V. The TS behavior can be also optimized by choosing suitable compliance current during a voltage sweep. Simulations of nanoparticles diffusion are also carried out to study the mechanism of this bidirectional TS process. The simulations show that this behavior can be attributed to the outer diffusion of Ag nanoparticles from an Ag electrode and their accumulation near the Pt electrode under the voltage sweep, which can serve as an additional counter active electrode. This work illustrates that Ag/Ta2O5/Pt diffusive devices are promising candidates for selector applications in bipolar memristor crossbar arrays.