All 3D-Printed Cu-PLA Composite Crossbar Memristor Array by Fused Filament Fabrication: Opportunities and Challenges

This study demonstrates the fabrication of all 3D-printed crossbar memristor arrays using material extrusion-based fused filament fabrication. The fused deposition is done using a copper-polycaprolactone filament (Cu-PCL) for electrodes and copper-polylactic acid (Cu-PLA) for an active layer. The memristor demonstrated bipolar switching, with a set and reset voltages of ∼16 and −8 V, respectively, and an on/off ratio of ∼100. The double logarithmic I–V plots showed ohmic behavior of the low-resistance state and nonlinear behavior for the high-resistance state with two different slopes ∼2.2 and 4.3, attributed to space-charge-limited current and trap-charge-limited conduction. Retention tests confirm the stability of the device over long periods. Statistical analysis of many such devices confirmed the reproducibility. Studies using bronze-PLA, carbon fiber PLA, and carbon fiber-acrylonitrile butadiene styrene have not shown any memristive behavior. The long-term potentiation and depression behavior of the Cu-PLA memristor device demonstrated synaptic learning, with nonlinearity factors of 21.27 and 47.62, respectively. The filament formation and the mechanism of resistive switching are studied employing Black’s equation, where a critical current of 50 μA for electromigration of copper through PLA matrix and a mean-time failure of 1.7 s for filament formation is observed. The study finds the electromigration of copper ions through surface diffusion, filling the voids at the interface of the PLA polymer. Migration of these ions through the defect and voids in the polymer matrix toward the next neighbor sequentially connects all the intermediate copper particles, forming a conductive filament.