Electrical bistable behaviors of organic materials in a single-layer structure

Abstract

The electrical bistable behavior of two organic materials, 2-amino-4, 5-imidazole-dicarbonitrile (AIDCN) and 2-(4-Diphenylamino-benzylidene)-malononitrile (DBMN) were investigated. Samples were prepared in a single layer structure, namely Al electrode/ organic material layer/ Al electrode. The Al electrodes and the AIDCN layer were formed with vacuum evaporation, and the DBMN layer was formed with spin coating. The specimens were initially electrical insulators (off-state) at low applied voltage. Beyond a critical value of voltage, the current suddenly increased by several orders. They remained in the low impedance state (on-state) even when the voltage was lowered below the critical value. The results of the surface observations with an atomic force microscope and the structure analysis with X-ray diffraction indicated that the AIDCN layer was composed of multi-crystalline grains, whereas the DBMN layer was amorphous. The on-state current was proportional to the square of the applied voltage, which suggested it was limited by space charge in the organic layer. The on/off transition behaviors and the surface morphology suggested that the transition of AIDCN would be due to tunneling charge injection caused by the charge accumulation at the interface between the organic layer and the metal electrode. The transition of DBMN would be the one between the states of almost equal energy levels, such as a change of polarization direction.