Synaptic behaviour of TiO x /HfO 2 RRAM enhanced by inserting ultrathin Al 2 O 3 layer for neuromorphic computing

Abstract The synaptic linearity of resistive random-access memory (RRAM) based on TiO x /HfO 2 improved by inserting an ultrathin Al 2 O 3 layer is investigated. A gradual bipolar switching with a positive set and a negative reset is observed for devices with an Al 2 O 3 layer after an electroforming process. The devices with a 1 nm Al 2 O 3 layer exhibit acceptable reliability with >400 cycles DC endurance with no decrement of the on/off ratio after 10 4 sec. A remarkable enhancement in the synaptic linearity of potentiation 2.15 and depression 1.52 is achieved in this device. The conduction mechanisms at different current regions of the optimized device are studied. The presence of the Al 2 O 3 layer is confirmed by x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy analyses. About 42% of the oxygen vacancy concentration calculated from the XPS spectra is responsible for the synaptic properties. This synaptic RRAM structure is suitable for upcoming neuromorphic computing devices.