Switching effect in Cu:TCNQ charge transfer-complex thin films by vacuum codeposition

We demonstrate the operation of an organic switching device using a uniform poly-crystalline Cu:7, 7, 8, 8-Tetracyanoquinodimethane (TCNQ) charge transfer (CT)-complex thin film that is prepared by vacuum vapor codeposition. Characteristic CT-absorption at λ=600–1200 nm was observed in the complex film in the UV-visible spectrum and the cyano stretching peak in the IR spectrum shifted to a higher (more than 29 ${\mathrm{cm}}^{\text{−1}})$ wave number than that of a pristine TCNQ film, suggesting the formation of a CT-complex in the evaporated thin film. Reproducible electrical switching characteristics were observed in the indium tin ${\mathrm{oxide/Al/(Al}}_2{\mathrm{O}}_3)\mathrm{/Cu:TCNQ/Al}$ structure. The device exhibited a clear threshold from low impedance to high impedance at an applied voltage of 10.0±2.0 V and a reverse phenomenon at a negative bias of −9.5±2.0 V. In this study, we demonstrate that a thin ${\mathrm{Al}}_2{\mathrm{O}}_3$ layer between the aluminum (Al) anode and Cu:TCNQ layers creates reproducible switching.