Bistable Resistive Memory Switches fabricated by Floating Thin Films of Conjugated Polymers

The layer-by-layer (LBL) fabrication of conjugated polymer (CPs) thin films while preserving their microstructural features by solution processing is highly desired for compact and flexible electronic circuits. However, it is cumbersome and challenging owing to the unavoidable damage to the underlying layers. To circumvent this issue, the unidirectional floating-film transfer method (UFTM) was utilized for the LBL fabrication of oriented CP thin films on the orthogonal liquid surfaces. Further, resistive bistable memory switches were fabricated by sandwiching a layer of metal nanostructures between the LBL-fabricated oriented CP thin films. The resistive switching phenomena were realized by utilizing the applied bias-dependent charge trapping, holding, and recombination on the available states at vacuum-deposited aluminum nanostructures. The effect of CP backbone conformation on the vertical charge transport was also analyzed via a comparative study of three thiophene-based polymers namely RR-P3HT, PBTTT, and PTB-7. It was revealed that CPs with relatively fewer hydrophobic side chains was more favorable for the facile vertical charge transport due to its preferred face-on conformation on the hydrophilic liquid substrate used in UFTM. It was demonstrated that a non-volatile bistable resistive memory switch fabricated using UFTM-processed oriented thin films of PTB-7 exhibited a remarkably high on-off ratio of 1.5 × 10⁶ with high durability.