  Both analog and digital resistive switching are essential components in the
neuromorphic computing system. This work reports the influence of Cu ions for
the transformation of analog to digital resistive switching in ITO/NiO/Ag
memristor devices. The undoped and low-concentration Cu doping illustrates the
analog switching, whereas higher doping demonstrates the digital
characteristics. At higher bias voltage, the Schottky barrier is developed at
both ITO/NiO and NiO/Ag interfaces. The increasing and decreasing of current
conduction with the escalating number of cycles for both the polarity in
undoped and low doped is elucidated by the electrode-dominated mechanism in
terms of reduction and enhancement of Schottky barrier height at the interface,
respectively. The digital switching characteristic due to the formation and
rupturing of the vacancy filament at higher doped sample is induced due to the
boosting of vacancies above the critical amount using ion implantation. The
synergic effect of current conduction due to local Cu migration and oxygen
vacancies can be utilized as a learning and forgetting process for neuromorphic
applications.
