Describing the analog resistance change of HfOx-based neuromorphic synapses using a compact series trap-assisted tunneling and Ohmic conduction model

Changes in the resistance of Ti/HfOx synapses are known to be governed by a thin-oxide barrier associated with the oxidation/reduction of a Hf-rich conducting filament (CF). However, experimental characterization of the CF is challenging. Critical physical properties and processes, such as the barrier location, time-dependent thickness during analog pulsing, and the temperature-effect on current, need to be better established. In this work, a compact model based on Trap-Assisted-Tunneling and Ohmic transport is utilized to analyze the analog switching of HfOx synapses. The model agrees well with the experimentally observed current–voltage relation and its temperature dependence. The extracted barrier heights during analog pulsing are consistent with a barrier situated near the reset anode; the electrode is opposite to the Ti oxygen-reservoir layer. A Finite Element Analysis simulation, which incorporates oxygen-vacancy migration, independently supports this conclusion. The model further permits extraction of the barrier thickness in relation to the analog pulses.