Coexistence of bi-stable memory and mono-stable threshold resistance switching phenomena in amorphous NbO _x films

Both bi-stable memory and mono-stable threshold switching are observed in amorphous NbO _x films. In addition, the transition between memory and threshold switching can be induced by changing external electrical stress. Raman spectroscopy and transmission electron microscope data show that the NbO _x film is self-assembled into a layered structure consisting of a top metal-rich region and a bottom oxygen-rich region. The volume ratio of the two regions depends on the film thickness. Our experimental results suggest that different characteristics of conducting filaments in the two regions result in thickness dependence of switching types and the transition between memory and threshold switching.