selector devices*

A metal-to-insulator transition (MIT) occurs in NbO₂ at high temperature coincident with a subtle change in its crystal structure. Because a similar transition occurs when sufficient electrical current is driven directly through the material, NbO₂ is being considered for use as a selector in crossbar memory arrays. Theoretical studies presently disagree as to whether the bias-induced transition is simply the MIT triggered by Joule heating, or a distinct transition triggered by electric field effects. Using novel scanning transmission electron microscopy (STEM) techniques based on electron beam induced current (EBIC) imaging, we map current paths, potential, and temperature in functioning, thin-film NbO₂ devices. We observe the bias-induced switching process at various stages, including the high-resistance state, the intermediate negative differential resistance regime, and the low-resistance state both with and without thermal runaway.