New Nonvolatile Memory Effect Showing Reproducible Large Resistance Ratio Employing Nano-gap Gold Junction
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0997-I04-08
New Nonvolatile Memory Effect Showing Reproducible Large Resistance Ratio Employing Nano-gap Gold Junction Yasuhisa Naitoh1,2, Masayo Horikawa1, and Tetsuo Shimizu1 1 Nanotechnology Research Institute, Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8562, Japan 2 Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, 4-1-8, Honcho, Kawaguchi City, Saitama, 332-0012, Japan ABSTRACT A large negative resistance is observed in the I-V characteristics of gold nanogap junction when high-bias voltages are applied. This phenomenon is characteristic behaviour on the nanometre scale; it only occurs for gap widths slightly under 13 nm. Furthermore, this junction exhibits a non-volatile resistance hysteresis when the bias voltage is reduced very rapidly from a high level to around 0 V, and when the bias voltage is reduced slowly. This non-volatile resistance change occurs as a result of changes in the gap width between the metal electrodes, brought about by the applied bias voltage. INTRODUCTION Recent research reports have described resistance switches using nanoscale spaces. Most switches of this type are composed of organic molecules possessing a switching effect sandwiched between two metal electrodes. Recently, there has been vigorous debate regarding whether the switching effects of these materials is due to the formation of metal filaments between the electrodes [1, 2]. In this study, the authors observed a reversible resistance switching effect in a structure composed of metal electrodes separated by about a 10 nm [3]. The structure of the device described here is relatively simple, requiring no molecules having complicated structures or special combinations of materials, but just simply consisting of Au electrodes on a SiO2-coated Si substrate. These devices are non-volatile with large on-off ratio and long retention time, and have the potential to be used for memory or storage devices without the need for any revolutionary technological advances. This report describes the resistance switching effect and the mechanisms of such a simple metal nanogap junction. EXPERIMENTAL DETAILS Sample preparation Figure 1 (a) shows a schematic diagram of the nanogap junction. The nanogap junction structure was constructed on a Si substrate coated with a 300-nm-thick thermally oxidized layer. The devices were fabricated by two cycles of photolithography and shadow evaporation. The width of the gap can be controlled by varying the evaporation conditions. In this study, the authors typically used nanogap structures with gap widths which are less than 10 nm. A range of thicknesses was created in the first step to allow control of the nanogap width. The details of fabrication procedure are described in elsewhere [4, 5]. The FESEM image of figure 1 (b) clearly
shows that the second metallic layer was created having an approximately 10-nm gap parallel to the edge of the underlying layer. Gaps that were shown by FESEM to have widths greater than 5 nm had
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