Enhanced Long-Term Memory (LTM) of BTO-/ZQDs-Based Optoelectronic Synapse

Abstract

This work investigates the enhancement of long-term memory (LTM) in optical synaptic photodetectors based on ferroelectric barium titanate (BTO) and ZnO quantum dots (ZQDs). The low-cost, solution-processed spin-coating technique is employed to fabricate the photodetectors, with successive deposition of BTO, ZQD, and Ag interdigitated metal–semiconductor–metal (MSM) electrodes on a quartz substrate. The ZQDs film was grown over the preannealed BTO layer (at $700~^{\circ }$ C). The complete BTO/ZQDs bilayer structure was finally annealed at $450~^{\circ }$ C. The variation in annealing temperatures introduces interface states between BTO and ZQDs, where the electrostatic potential arises from BTO. The self-polarization nature of BTO played a crucial role in enhancing photocharge carrier generation and suppressing charge recombination. The fabricated photodetector demonstrated a higher excitatory postsynaptic current (EPSC) under UV illumination and a significantly slower decay rate of photocurrent after UV exposure compared to a ZQDs-based device (without BTO). This slower decay indicates an improvement in LTM retention time (from 6.57 s for the device without BTO to 96.81 s for the BTO/ZQDs-based device) for 90% threshold, and it approaches ~3000 s for 30% threshold. This work presents the fabrication, characterization, and performance analysis of BTO/ZQDs/Ag-MSM photodetectors, emphasizing their potential for EPSC enhancement and LTM applications in neuromorphic computing. Also, the photosensitivity and responsivity of the BTO/ZQDs-based device are ~39 and 11.8 times higher than those of the ZQDs-based device, respectively.