Electrical switching, loop hysteresis and charge oscillation in VO$_{\mathrm{\mathbf{2}}}$\textbf{ micro-channel devices}

Functional metal oxides are essential materials to realize novel electronic and optoelectronic devices with unique tunable characteristics. Vanadium dioxide (VO$_{\mathrm{2}})$ is of particular importance due to its well-known reversible metal-to-insulator phase transition which occurs at \textasciitilde 68\textdegree C temperature. In this work we investigated the electrical switching characteristics, loop hysteresis and negative differential resistance (NDR) of micro-channel devices using VO$_{\mathrm{2\thinspace }}$thin films deposited on sapphire ($c$-cut) substrates. The devices exhibited self-sustained charge oscillations with large amplitude modulation when connected to a DC power source and does not require any external capacitive or inductive components. We demonstrate that the device oscillation frequency can be systematically tuned by varying the optical power of a CW external laser source focused on the top of the VO$_{\mathrm{2}}$ micro-channels. This result is attributed to changes in electrical resistivity of the VO$_{\mathrm{2\thinspace }}$channel under illumination which in turn changes the NDR voltage width region and therefore the oscillation frequency.