Methodology to characterize physical properties of electrode/dielectric interfaces using sub-micrometer-scale measurements

Charge generation and accumulation in dielectric polymers remain critical. An accumulation of charge may disturb the local electric field and potentially lead to insulation failure. It is essential to understand the physical mechanisms governing space charge behaviour in order to predict electric field distributions under stress and to enhance insulation reliability. One major challenge is the determination of structural and electrical properties of interfaces between the dielectric and the electrode (metal or semiconductor (SC)) at the sub-micrometer scale. It is essential to consider roughness or chemical/physical defects (trap states) at the interface, as well as charge transfer between two materials in contact, which can strongly influence charge generation processes at the interface. In this work, a new methodology to characterize and determine charge distribution at a semiconductor/low density polyethylene (SC/LDPE) interface using electrical modes derived from Atomic Force Microscopy (AFM) is proposed. Kelvin Probe Force Microscopy (KPFM) method is used to probe the surface potential on SC/LDPE interface cross-section. Charge density profiles are extracted from a method based on Poisson's equation using a double derivation of the surface potential distribution through KPFM data. A parametric study to optimize the determination of the charge density profile is performed to identify the best compromise between spatial resolution and noise. Also, the measured charge density and the method are validated using a Finite Element Method (FEM) model which reproduces the shape of experimental potential. By applying this method, results highlight the charge accumulation at the interface, with negative charges on SC side and positive charges in LDPE. Furthermore, this approach allows the physical interpretation of energy levels of each material.