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 Ion/Ioff 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.