Nanoscale Conductivity Mapping: Live Imaging of Dielectric Breakdown with STEM EBIC

Dielectric breakdown (DB) is central to the failure and function of modern and next-generation computing components. Despite its importance in microelectronics, the specific mechanisms leading to DB are poorly understood. Electrical testing provides little spatial information about the small-scale effects that precede breakdown. High resolution imaging techniques, such as transmission electron microscopy (TEM), have the requisite resolution but are almost exclusively used to study the post-mortem effects of catastrophic DB. In this study we present techniques to directly visualize DB in nanoscale devices with scanning TEM electron beam-induced current (STEM EBIC) imaging. STEM EBIC imaging maps local conductivity and electric field with high contrast. In HfO2-based resistive memory (RRAM) devices, a data bit is stored as a conductive path formed via controlled, reversible DB. With STEM EBIC we image Ti/HfO2/Pt devices capable of switching repeatedly in situ. Distinct regions of soft and hard dielectric breakdown are observed at different phases of RRAM cycling. These results suggest a model where DB occurs on a progressive continuum between hard and soft breakdown.