Light-stimulated long-term potentiation behavior enhanced in a HfO2/InGaZnO photonic synapse

•Investigation of the HfO2/InGaZnO photonic synapse device.•Enhanced long-term-memory functionality by HfO2 passivation.•Realization of 1024 multi-level states and 3-bit non-volatile memory capacity.•High activation energy for recombination of ionized oxygen vacancies, enabling long-term potentiation induction. Photonic-based neuromorphic systems offer numerous advantages, including low crosstalk, high bandwidth, and low power consumption, making them an ideal choice for ultrafast neuromorphic systems. Although these neuromorphic systems promote the utilization of amorphous oxide semiconductors (AOSs) for promising photonic synapses, precise control of their unique persistent photoconductivity to mimic synaptic plasticity using an external light stimulus has rarely been studied. This study investigates the significant enhancement of the long-term potentiation (LTP) behavior in an InGaZnO (IGZO) photonic synapse through facile HfO2 passivation. In HfO2/IGZO synapses, the HfO2 layer is crucial in enhancing the LTP characteristics. The improvement in the persistent photocurrent behavior of the HfO2/IGZO synapse was attributed to the higher activation energy required for the neutralization of ionized oxygen vacancies, facilitating the LTP behavior. The LTP was dynamically modulated depending on external light pulse conditions. A large number of multilevel states (1024 states) were enabled by consecutive light simulations. Furthermore, HfO2/IGZO synapses exhibit different learning capacities depending on the external stimuli configuration. These findings demonstrate our ability to manipulate synaptic functionality in AOS-based artificial photonic synapses, paving the way for multifunctional photonic synapse circuitry. This advancement holds the potential for realizing an artificial vision system in the future. [Display omitted]