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UBC Theses and Dissertations

The importance of Joule heating on the voltage-triggered insulator-to-metal transition in VO₂ Spitzig, Alyson


The large change in resistivity in the material VO₂ has attracted considerable attention since it was first discovered in 1959. Recently, the ability to trigger the insulator-to-metal transition (IMT) with a strong electric field has been observed, but there has been debate about whether the transition is due to field-effects. We apply a voltage bias across a VO₂ thin film via a conductive atomic force microscope (CAFM) tip and measure the resultant current. We observe the IMT as a jump in the measured current in the IV curves. We fit the IV curves to the Poole-Frenkel (PF) conduction mechanism in the insulating state, immediately preceding the IMT. The PF conduction mechanism describes the thermal excitation of electrons into the conduction band in insulators, facilitated by strong electric fields. The PF mechanism is temperature dependent, and we use the temperature dependence to calculate the local temperature of the film before the transition. We directly compare the local electric field and local temperature of the film immediately preceding the IMT. We determine that the transition is not solely due to the applied electric field, but rather that the tip has locally warmed the film close to its IMT temperature through Joule heating.

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