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D7.1.1

Polymer electrical bistable device and memory cells Jianyong Ouyang, Chih-Wei Chu, Ankita Prakash, and Yang Yang Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095, U.S.A. ABSTRACT Electrical bistable states with the conductivity different by more than four orders in magnitude were observed in a polymer film sandwiched between two metal electrodes. This polymer film was composed of gold nanoparticles, 8-hydroxyquinoline and polystyrene, and was formed by a solution process. The film can be programmed between the two electrical states by an electric field. The as-prepared device, which was in a low conductivity state, exhibited an abrupt increase of current when the device was scanned up to 2.8 volt (V). The high conductivity state can be returned to the low conductivity state at a voltage of –1.8 V in the reverse direction. The device has a good stability in both the states. The transitions are nonvolatile, and the transition from the low to the high conductivity state takes place in nanoseconds, so that the device can be used as a low-cost, high-density, high-speed, and nonvolatile memory. The switching mechanism was studied by investigating the current-voltage characteristics, the temperature dependence of the current, the surface potential atomic force microscopy and the energy levels of the materials. The electronic transition is attributed to the electric-field induced charge transfer between the gold nanoparticles and 8-hydroxyquinoline molecules. INTRODUCTION Organic semiconductor devices such as light-emitting diodes [1,2], photovoltaic cells [3], and transistors [4] have aroused considerable interests because of the unique advantages provided by organic materials and devices. These advantages include low fabrication cost, high mechanical flexibility, and versatility of the chemical structure. However, electronic memory using organic materials is still in the exploration stage. Though three-terminal transistors, using ferroelectric polymers [5], and two-terminal bistable devices, which exploit charge transfer between metal atoms and organic compounds [6 ,7], exhibit interesting performance, they are far from practical applications in memories. A new electronic bistable device with a triple-layer structure, two organic layers and a middle discontinuous metal layer, sandwiched between two metal electrodes exhibits promising performance and can be used as nonvolatile memory [8-10]. However, the fabrication of this device is through thermal evaporation in high vacuum, and stringent conditions are required to control the morphology of the middle, discontinuous metal layer. Möller et al reported a memory device using conducting polymers, but this device can be written only once and can not be used as nonvolatile memory [11]. A two-terminal electronic bistable device, which can be fabricated through solution processing and can be written/erased many times, should be the target for organic memory. Recently, we successfully demonstrate an electronic bistable devic