Inkjet-printed transparent zinc oxide optoelectronic synapse with photoinduced artificial plasticity

The development of scalable and cost-effective fabrication strategies for artificial synapses is critical for next-generation neuromorphic systems aimed at overcoming the von Neumann bottleneck in data-intensive applications. In this context, inkjet printing offers an attractive fabrication route by combining scalability, low processing cost, and compatibility with solution-processable metal oxides. Using this strategy, a fully transparent optoelectronic synaptic device based on inkjet-printed ZnO thin films in a planar interdigitated ITO configuration is reported. Under 365 nm illumination, the device exhibits persistent photoconductivity and successfully emulates key synaptic functions, including excitatory postsynaptic current, paired-pulse facilitation, short- and long-term plasticity, and learning behavior. In particular, the proposed synapse achieves a paired-pulse facilitation index exceeding 220% at a low operating bias of 100 mV, together with forgetting times of up to 146 s and a 33% reduction in relearning pulses. These metrics compare favorably with previously reported sputtered ZnO-based optoelectronic devices, highlighting the potential of inkjet-printed ZnO as a transparent and scalable platform for artificial optoelectronic synapses.