Realization of Short- and Long-Term Memories at Nanoscale and their Temporal Evolution in Two-Terminal Memristive Synapses

Abstract

Two-terminal memristors are recognized as potential ingredients to build electronic synapses for in in-memory computing applications with high density integration. However, the requirement of electro-forming process and instability in operational performances limit their prospects. Moreover, it remains a challenge to achieve both long- and short-term memories (LTM and STM) in a single device owing to the entirely different mechanisms governing the respective functionality. In this work, employing local probe techniques, it is demonstrated that a forming-free, two-terminal TiOx memristor can be realized as arrays of a large number of nanoscale synaptic devices. A real time visualization of the temporal evolution of LTM and STM is presented which, in support of various measurements, indicates a reversible soft breakdown in the active layer, leading to a high memory retention for LTM. The STM, on the other hand, is governed by the charge carrier trapping/detrapping at defect sites. The results not only demonstrate different synaptic features in a solid state memristor at nanoscale but also provide a fundamental understanding of their working mechanisms. This will be useful for future neuromorphic devices.