Electrical bistable device with high switching voltage is developed. The device structure is Al electrode layer/ metal dispersed layer/ organic material layer/ Au electrode layer, whose thickness is 60/30/80/60nm, respectively. The organic material is a type of bisquinomethane, 2, 5-bis {(3’, 5’-di(tert-butyl)-4’-oxocyclohexa-2’, 5’-dienylidene)-(4"-methoxyphenyl) methyl} thiophene (DODMT). The metal dispersed layer is formed by co-evaporation of DODMT and Al. With this structure, the switching voltage around 18V is attained. The device works even without the metal dispersed layer, in that case, with switching voltage of around 5V. The origin of bistability is estimated to be tunneling charge injection caused by charge accumulation at the Au/organic interface and subsequent enhancement of electrical field. Charge accumulation has also been observed in the metal dispersed layer. It would retard charge injection from Al electrode to DODMT layer, and consequently, to the Au/organic interface, and make the switching voltage high.
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.
Crystallization kinetics of Ge2Sb2Te5 phase-change recording films were studied through the isothermal annealing test, the static laser annealing test, and the static/dynamic observation by transmission electron micrographs. It has been considered that the crystallization of recorded mark at erasing process dominated by the crystal growth, where the crystalline nuclei had already produced during recording process of the mark.
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