Temperature-induced metal-to-insulator transition in epitaxially grown NbO₂ films

Transition metal oxides demonstrating metal-to-insulator transitions (MIT), such as VO₂ and NbO₂, are widely studied materials for use as selector elements in resistive random-access memory (RRAM). The MIT transition temperature (T_MIT) of VO₂ is close to room temperature (~340 K). NbO₂, on the other hand, has a much higher transition temperature (T_MIT = 1081 K), which complicates the direct observation of the MIT in thin films and has not been reported in an epitaxial film, so far. In this presentation, we will demonstrate temperature dependent electrical resistivity of epitaxially grown NbO₂ thin films revealing the actual mechanism of MIT in NbO₂. High-quality epitaxial films were grown using pulsed laser deposition and structural characterization was performed using x-ray diffraction and atomic force microscopy. The resistivity of the as-grown films was measured from room temperature to 1100 K under a controlled environment using the four-probe resistivity measurement technique. Also, we will examine the effect of epitaxial strain to MIT of NbO₂ was demonstrated by varying thickness of the films from 12 to 45 nm