Improvement on synaptic properties of WO x -based memristor by doping Ti into WO x

Abstract

Doping Ti into WO x is widely used to improve the performance of various WO x -based devices. However, Ti-doped WO x (Ti:WO x ) based memristors have not been investigated in depth, especially regarding their synaptic properties. In this report, Ti:WO x films are deposited by sputtering WTi alloy target in Ar + O2 atmosphere, in which the substrates are not heated, avoiding the precipitation of TiO2 phase. As-grown Ti:WO x films exhibit polymorphous crystallized structures, originating from the topological deformation of WO6 octahedron by replacing W with Ti. Furthermore, the memristor with the structure of W/Ti:WO x / indium-doped tin oxide demonstrates typical synaptic properties, including the controllable synapse weight update by adjusting the input pulse amplitude, interval, as well as the transformation from the paired-pulse facilitation to the paired-pulse depression. Moreover, the higher Ti–O band energy leads to smaller hysteresis loop areas of its current–voltage (I–V) curves, which may mean better synaptic performances, such as higher resolution. Additionally, contrary to other metal-oxide based memristors, our device conductance increases by applying positive voltage scans or a series of positive pulses on the metal electrode. Otherwise, it will decrease. With I–V fitting and the energy-band diagrams, we analyzed deep carrier transport processes, revealing a unique synaptic mechanism.