Characteristics of Organic Memory Using Metal Oxide Nano-Clusters
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Characteristics of Organic Memory Using Metal Oxide Nano-Clusters You-Wei Cheng1, Tzu-Yueh Chang1,2, and Po-Tsung Lee1,2 1 Department of Photonics & Display Institute, National Chiao Tung University, 1001 University Road, Hsinchu 300, Taiwan 2 Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, 1001 University Road, Hsinchu 300, Taiwan ABSTRACT In this report, electrical properties of an organic memory device with a tri-layer structure, MoO3 nano-clusters layer sandwiched between Alq3 thin films, are investigated. The device using this kind of structure exhibits a large ON/OFF current density ratio over 104, long retention time over 1hr, and an electrically programmable character. The formation of the bistable resistance switching of the device originates from a charge trapping effect of the MoO3 nano-clusters layer. Moreover, the current density-voltage (J-V) characteristics of the device are quite different from those of organic bistable devices (OBDs) using MoO3 nano-particles. No negative differential resistance is observed in the J-V curve of the device. This may be due to the distinct surface morphology of the MoO3 layer on the Alq3 thin film. INTRODUCTION In past decades, conjugated organic materials have been widely applied in organic electronic and optoelectronic devices such as organic thin film transistors, organic light emitting diodes, organic photovoltaic cells, etc. One of candidates for next generation memory devices, an organic memory device, is emerging because of greater scope for better scalability, low-cost fabrication, mass production capability, and mechanical flexibility. Many published results have paid attention to organic memories with nano-structured materials [1-7] (e.g., nano-cluster/organic-metal composite layers [1-3], nano-composites of polymer-gold nano-particles [4-6]) inside an organic layer(s) as charge trapping centers. Because of distinct properties of the nano-structured materials, organic resistance switching memories with high density, large ON/OFF ratio, and other superior performances can be obtained in the near future. Molybdenum trioxide (MoO3) has been extensively applied in organic optoelectronics (e.g., as a doping layer to raise conductivity [8]). Such wide applications are attributed to the characteristics of the MoO3 thin film: high work function, high conductivity for holes, and high transparency. In this report, electrical characteristics of an OBD with an Alq3/MoO3 nano-clusters /Alq3 tri-layer structure are studied. The OBD shows a large ON/OFF current density ratio over 104, long retention time over 1hr, and a rewritable/reerasable feature. The resistance switching mechanism of the OBD resulted from a charge trapping effect of the MoO3 nano-clusters layer. Moreover, no negative differential resistance (NDR) showed in the J-V curves of OBDs using MoO3 nano-particles [7] is observed in the J-V curve of the OBD. This may ascribe to the different surface morphology of the MoO3 layer on the Alq3 thin film
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