HfO2 based MIS type RRAM as an Electronic Synapse

We demonstrate the potential of MIS (metal-insulator-semiconductor) type RRAM as an electronic synapse. The fabricated RRAM stack, $\mathrm{n^{+}-Si/HfO_{2}/Ti/Al}$ shows pertinent switching only when formed in inversion regime. This can be attributed to role played by an oxide interfacial layer (IL) formed at the HfO2/Si interface and oxygen scavenging layer of Ti metal over the HfO2 layer and the variation in density of oxygen vacancies at the respective interfaces, in filament formation and rupture mechanism. The multiple resistive states are attained by the controlled sweeping to emulate the synaptic behavior. Here with the help of physical model we tried to explain switching of a MIS RRAM and demonstrate the learning of a synapse using STDP which shows the change in device conductance as a temporal function of spiking order. We experimentally corroborate that proposed MIS type RRAM manifests bio-synaptic behavior akin to MIM stack and shows feasibility to be deployed as an artificial synapse for neuromorphic applications.