Mechanism of soft and hard breakdown in hexagonal boron nitride 2D dielectrics

In this study, we investigate the physical mechanism of soft and hard dielectric breakdown using conductive atomic force microscope (CAFM) as a nanoscale spectroscopy tool on blanket hexagonal boron nitride (h-BN) films with thickness of ~ 4 nm grown on Cu substrate. The soft breakdown regime involves vacancies/defects (boron and/or nitrogen) rich percolation path formation while the hard breakdown regime shows nano-pore formation that involves removal of h-BN layers and formation of a metallic contact due to CAFM tip adhesion with the Cu substrate. Reduction of Weibull slope for successive soft breakdown events due to multiple ramp voltage tests at each location confirms the validity of the percolation model. We observe a concavity in the breakdown voltage distribution that can be explained by the thickness variations in h-BN layers. The clustering model is shown to be good candidate to describe the breakdown voltage distributions.