Charge-Trapping-Enhanced Resistive Switching and Charge Storage in Silk Fibroin-TiO₂ Composite Memristors

Silk fibroin (SF) is a promising bio-compatible material for transient and bio-integrated memory devices; however, its relatively high leakage current and limited resistance state stability remain critical issues. In this study, Ag/SF-TiO₂/Pt bio-memristors were fabricated using SF-TiO₂ composite films with TiO₂ nanoparticle concentrations of 0, 0.25, 0.5, and 1.0 wt%. SEM analysis showed that TiO₂ incorporation increased particle aggregation while maintaining continuous film morphology. Optical analyses revealed that TiO₂ nanoparticles reduced the apparent optical gap, enhanced sub-bandgap absorption, and suppressed photoluminescence intensity, indicating the formation of defect- and trap-related states. Electrical measurements demonstrated that TiO₂ incorporation effectively reduced leakage current and stabilized the high-resistance state. The devices exhibited stable bipolar resistive switching within ±1 V, with enhanced I_on/I_off ratios of approximately 10⁴-10⁵ after TiO₂ addition. Endurance and retention measurements confirmed reliable switching over 100 cycles and stable resistance states up to 10⁴ s. Capacitance analysis further revealed resistance state-dependent charge storage behavior, with higher capacitance in the low-resistance state due to conductive filament formation and TiO₂-assisted interfacial polarization. These results indicate that TiO₂ nanoparticles effectively modulate charge trapping, leakage suppression, and memory stability in SF-based bio-memristors.