Organic Thin-Film Memory
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Organic Thin-Film Memory
Yang Yang, Liping Ma, and Jianhua Wu Abstract Recently, organic nonvolatile memory devices have attracted considerable attention due to their low cost and high performance. This article reviews recent developments in organic nonvolatile memory and describes in detail an organic electrical bistable device (OBD) that has potential for applications. The OBD consists of a tri-layer of organics/metal nanoclusters/organics sandwiched between top and bottom electrodes. A sufficiently high applied bias causes the metal nanoparticle layer to become polarized, resulting in charge storage near the two metal/organic interfaces. This stored charge lowers the resistance of the device and leads to an electrical switching behavior. The ON and OFF states of an OBD differ in their conductivity by several orders of magnitude and show remarkable bistability—once either state is reached, the device tends to remain in that state for a prolonged period of time. More important, the conductivity states of an OBD can be precisely controlled by the application of a positive voltage pulse (to write) or a negative voltage pulse (to erase). Device performance tests show that the OBD is a promising candidate for high-density, low-cost electrically addressable data storage applications. Keywords: nonvolatile memory, OBD, organic electrical bistable devices, rewritable memory, thin films.
Brief Review of Recent Works on Organic Memory Organic memory devices are generally realized by interposing thin layers containing organic materials between two electrodes. One way to achieve this is by using an x–y addressable array format. The array is formed by the cross-points between the parallel bottom electrodes in the x direction and the parallel top electrodes in the y direction.1 This format may soon be realized in practical applications, but the data storage density it provides is limited by the cross-point area. Another method involves using probing heads to replace the top electrodes, where the active medium is deposited on top of a conducting substrate, which is used as the common electrode. Generally, scanning probe microscope (SPM) techniques are used for this kind of nanometer-scale memory,2 with the main advantage of using this technique being ultrahigh data storage density. One of the major drawbacks is that this technique holds little promise from a practical application point of view. In this article, we focus on x–y addressable organic memories.
MRS BULLETIN/NOVEMBER 2004
The advantages of organic memory devices include, but are not limited to, flexibility, easy processing, low cost, and largerarea fabrication by printing techniques. Another promising possibility is to stack several memory layers on top of each other to enhance the data storage density. Ferroelectric switching and conductance switching have been observed in organic memories. Ferroelectric polymers have a much lower permittivity and switching speed than inorganic ferroelectrics,3 which makes them less attractive. On the other hand, significant res
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