Recent research reports have described resistance switches using nanoscale spaces. Most switches are composed of organic molecules possessing a switching effect sandwiched between two metal electrodes, which consist of a great variety of materials, for example, conductive organic wires, carbon nanotubes, or amorphous carbon. Also, K. Terabe et al. have reported atomic switches that employ solid-state electrochemical reactions between Pt electrodes and AgS or CuS. (Terabe et al., Nature, (2005) 433, 47-50.) This atomic switch technology will be the basis to realize non-volatile memory devices for the next generation.
In this study, we observed a reversible resistance switching effect in a structure composed of metal electrodes separated by about a 10 nm gap. (Y. Naitoh et al, Nanotechnology (2006) 17 5669.) The structure of the device shown 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. A large negative resistance is observed in the I-V characteristics of this junction when high-bias voltages are applied. This phenomenon is characteristic behaviour on the nanometre scale. 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. The high and low resistance conditions were performed by the rapid and slow reductions of applied bias voltages, respectively. The maximum resistance ratio between high and low resistance was over six orders of magnitude.
This study is the first to describe a reversible resistance switching effect occurring across a nanogap between metal electrodes. It has been shown that this effect is peculiar to gaps on the nanometre scale, dependent on the gap width, and that its mechanism is speculated by the reversible migration of gold atoms. The resistance switching ratio can be adjusted by controlling the applied voltage, where it can tolerate over 10,000 cycles. Due to the simplicity of the construction of this device, it appears that this device has great potential for future application in non-volatile memory and other information storage devices.
|