Electrical Switching Properties of Planar Thin-Film Metal-Insulator-VO2-Metal Capacitors

The metal-insulator phase transition (MIT) of the VO2 in planar thin-film metal-insulator-VO2-metal capacitor structures allows realizing unique non-linear electrical switching properties and opens an exciting area of research. The MIT of VO2 is accompanied by an enormous reduction in electrical resistance and optical transmittance in the infrared spectral range, especially in the telecommunications window, and thus represents a promising material for hybrid optoelectronic integrated circuits [1,2]. In this work, we fabricate Au-SiO2-VO2-Ir planar thin-film capacitors on silicon. We show that VO2 can be epitaxially grown on Ir thin films on (001) silicon substrates, thus offering the possibility to integrate these capacitors and VO2-based devices into silicon technology. The Ir layer forms the backside capacitor plate of the Au-SiO2-VO2-Ir capacitor structure, the counter top electrode consists of a thin optically transparent Au film. Details on the growth of the epitaxial Ir layer on (001) silicon using a yttria-stabilized zirconia buffer layer can be found here [3,4,5].
The fabricated Au-SiO2-VO2-Ir capacitors with an area of about 3x3 mm2 were electrically investigated by temperature sweeps and I-V characteristics. A voltage dependent electrical leakage current with a pronounced hysteresis reveals unambiguously an electrically controllable capacitor response based on the MIT of the VO2 thin film. In this context, we also prove that ohmic heating effects can be ruled out. In the frequency range between 1 Hz and 1 MHz, measurements of the phase shift at different temperatures and bias voltages were performed on the capacitors. We show that VO2-based planar thin-film capacitors exhibit useful nonlinear electrical properties in DC and AC circuits and that they have potential applications in tunable nonlinear electronics, smart sensor technologies with memory effects compatible with silicon technology.
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