Crystal with Metal-Insulator Transition by Plasma Processing Technique and Its Application to Switching Devices

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In this project, we deposited vanadium dioxide (V0_2) films on Al_2O_3 substrates with metal-insulator transition (MIT) by using inductively coupled plasma (ICP)-assisted sputtering technique. In addition, we tried to fabricate a new switching device utilizing VO_2 film with MIT.First, we found that by selecting oxygen flow rate proper value compared to flow rate of Ar gas we can deposit stoichiometric film with MIT. Films under adequate conditions revealed MIT with three orders change in resistivity at temperature around 340 K. It was shown that this MIT is caused by crystalline structural transition from monoclinic phase to tetragonal phase through XRD analyses.Next, we fabricated a device of VO_2 with two terminal metal electrodes. We observed current jump phenomena by applying voltage to this device. We call this electric field-induced metal-insulator transition. When we decreased gap length between the two electrodes, threshold voltage that can trigger the electric field-induced MIT decreased. Thus we can control resistance change in this device by changing electrodes gap length.Finally, we fabricated two kinds of planar type devices with dimensions of the electrode gap of 5 μm and the electrode of 1500 μm and 10 μm /10 μm (electrodes gap /electrode width). In these devices, we observed fast resistance change phenomena within 200 ns. Low threshold voltage of 2 V was achieved in the former device, while large resistance ratio was achieved in the latter.Switching phenomena revealed in this project offer great interests not only in applications of VO_2 based planar device to functional electronic devices such as switching and memory devices but also in discussion on physical mechanism of switching phenomenon in oxide material with strong correlation.