Probabilistic insight to possibility of new metal filament nucleation during repeated cycling of conducting bridge memory

Abstract

The question of whether resistance switching in conducting bridge random access memory (CBRAM) devices occurs through a single filament which repeatedly undergoes nucleation and rupture or through different filaments for different cycles is difficult to ascertain using conventional electrical tests on metal–insulator–metal (MIM) capacitor structures. In order to profile the spatial location of the conductive filament during multiple switching cycles, we make use of the Ni–HfO2–Si based metal–insulator–semiconductor (MIS) stack with a transistor test structure so that the lateral location of the filament along the source to drain can be probed electrically by considering the weighted ratio of source and drain currents measured. Our analysis reveals that filaments can evolve in spatially uncorrelated locations and switching is not always caused by the same filament over and over again. A simple statistical model is also provided to justify the inferences of the electrical study. The probability of a new filament nucleating elsewhere in the dielectric is a strong function of the oxide barrier thickness as well as the curvature radii of the previously ruptured metal filament edges.