Memory Effect in Organic Diodes Containing Self-assembled Gold Nanoparticles
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Memory Effect in Organic Diodes Containing Self-assembled Gold Nanoparticles Hai Ping Wang1, SÈbastien Pigeon2, Ricardo Izquierdo3, and Richard Martel1 1 Regroupement QuÈbÈcois sur les MatÈriaux de Pointe et dÈpartement de Chimie, UniversitÈ de MontrÈal, C.P. 6128 Succursale Centre-ville, MontrÈal, H3T 1J4, Canada 2 OLA Display Corp, 1000 St-Antoine Ouest, suite 106, MontrÈal, H3C 3R7, Canada 3 DÈpartement d'informatique, UniversitÈ du QuÈbec ‡ MontrÈal, Case postale 8888, Succursale Centre-ville, MontrÈal, H3C 3P8, Canada ABSTRACT Electrical bistability is reported in metal-organic-metal diodes. The device consists of two Al electrodes separated by an organic layer that contains embedded Au nanoparticles (NPs) supported by parylene nanopillars. This paper presents results with two different organic materials: 2-amino-4, 5-imidazoledicarbonitrile (AIDCN) and aluminum tris(8hydroxyquinoline) (Alq3). Electrical characterization of the diodes shows bistability with two well-defined states with high (OFF) and low (ON) resistances. The ON/OFF ratio is 104 and current-voltage (I-V) curves show a negative differential resistance (NDR). The diodes can be programmed in either the ON or the OFF state and maintained it for at least 8 months in air without any evidence of degradation. This conspicuous memory effect is rationalized in terms of charge storage mediated by the oxidation/reduction of the NPs. The fabrication method is general and provides a good control on both the size-uniformity and the position of the Au NPs embedded in the organic materials. The diode characteristics with different NP density are also addressed.
INTRODUCTION There is a growing interest over the past few years in developing organic non-volatile memory devices. Different organic materials and device architectures have been explored for this purpose. A good example is the memory diode based on a three-layer organic/metal/organic structure embedded between two electrodes [1-6]. The device reliably switches at a threshold voltage (Vth) between the OFF and the ON conductive states and retain its programmed states even when the bias voltage is turned off. The organic bistable devices (OBD) made with different organic materials, such as 2-amino-4, 5-imidazoledicarbonitrile (AIDCN) [1-3], aluminum tris(8-hydroxyquinoline) (Alq3)[4,5] and pentacene [6], have shown strong bistable effects. The parameters that control the Vth and the ON/OFF ratio are however hard to tackle because they mostly depend on the detailed structure of the intermediate metal layer and, in some cases, on the presence of impurities in the organic layer. The OBD metal layer is in fact composed of nanoparticles (NPs) that are prepared by directly depositing a thin metal layer on top of an organic layer. The metal deposition process is simple, but it has important limitations and offers little control on the size distribution of the NPs. Our group recently reported on a new method to achieve good controls on the NPs size distribution, concentration and position inside the
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