The nature of column boundaries in micro-structured silicon oxide nanolayers
Columnar microstructures are critical for obtaining good resistance switching properties in SiO x resistive random access memory (ReRAM) devices. In this work, the formation and structure of columnar boundaries are studied in sputtered SiO x layers. Using TEM measurements, we analyze SiO x layers in Me–SiO x –Mo heterostructures, where Me = Ti or Au/Ti. We show that the SiO x layers are templated by the Mo surface roughness, leading to the formation of columnar boundaries protruding from troughs at the SiO x /Mo interface. Electron energy-loss spectroscopy measurements show that these boundaries are best characterized as voids, which in turn facilitate Ti, Mo, and Au incorporation from the electrodes into SiO x . Density functional theory calculations of a simple model of the SiO 2 grain boundary and column boundary show that O interstitials preferentially reside at the boundaries rather than in the SiO 2 bulk. The results elucidate the nature of the SiO x microstructure and the complex interactions between the metal electrodes and the switching oxide, each of which is critically important for further materials engineering and the optimization of ReRAM devices.