Electric-field-driven phase transition in vanadium dioxide

We report on local probe measurements of current-voltage and electrostatic force-voltage characteristics of electric-field-induced insulator to metal transition in VO${}_2$ thin film. In conducting AFM mode, switching from the insulating to metallic state occurs for electric-field threshold $\mathcal{E}\sim 6.5\times {10}^7{\mathrm{Vm}}^{-1}$ at $300$K. Upon lifting the tip above the sample surface, we find that the transition can also be observed through a change in electrostatic force and in tunneling current. In this noncontact regime, the transition is characterized by random telegraphic noise. These results show that electric field alone is sufficient to induce the transition; however, the electronic current provides a positive feedback effect that amplifies the phenomena.

Figure 1

(a) Temperature dependence of the in-plane resistance of the VO${}_2$ thin film deposed on doped silicon; (b) I(V) curves measured at 300 K, 330 K, and I(V)/10 measured at 360 K. Inset, AFM topography of the sample. (c) Zoom on the current jumps, indicated as a dashed box on (b).

Figure 2

(a) Tuning fork frequency shift $\Delta$$f$ vs. tip-sample voltage difference $V$ for the tip located at 35 nm above the surface. It shows the characteristic quadratic dependence of the electrostatic force with voltage. Small steps appear at high voltage, $\sim 7$ V, as shown in the inset with the parabolic background removed. They are the consequence of electric-field-induced IMT.

Figure 3

(a) Tuning fork frequency shift vs. time. From bottom to top, the first two curves are taken at two different places on the VO${}_2$ sample at 300 K; the third curve shows a time trace at 370 K in the metallic state and, finally, the upper curve is a time trace on a simple Pt thin film at 300 K. (b) Histograms of all time traces [using the same color code as (a)]. Curves are normalized to set their maximum to 100 counts for each histogram. Inset in (b), two-states fluctuator model discussed in text.

Figure 4

EFM time traces for different electrical-field values at 300 K. (a) The tip/sample distance is set to 35 nm and voltage is changed from 8 to 0 V. (c) The tip/sample voltage is set to 8 V and the tip/sample distance is varied from 30 to 130 nm. Panels (b) and (d) show the histograms of each time traces presented in panels (a) and (c), respectively. Non-Gaussian noise is only found for tip/sample distance below 90 nm and tip/sample voltage above 4 V.

Figure 5

I(V) curve in the tunnel regime.