Peering inside a functioning Pt/TiO$_{2}$/Pt bipolar resistance switching device

Many transition-metal oxides exhibit electrical polarization-dependent resistance changes. Direct observation of the physical changes induced during this switching has been limited, due to challenges in observing subtle material changes occurring in a small volume. We use x-ray absorption spectromicroscopy and transmission electron microscopy (TEM) in order to determine the chemical and structural identity of the switching region in a functioning Pt/TiO$_{2}$/Pt device, fabricated on a thin transparent window. These transmission techniques allow probing of the physical properties of the switching layer between/during the application of an electrical bias. We directly observed the formation of a conductive channel following an electroforming process. The conductive channel is identified to be a nanoscale metallic suboxide (TiO$_{2-X})$, a phase generated within the TiO$_{2}$ matrix by the creation and ordering of oxygen vacancies. Besides shedding light on long-standing questions regarding the physical changes, we show how this work has informed new device engineering.