Leakage current as a probe into the mechanics of carrier transport in insulating composite polymers

Abstract

Amorphous composite polymers are widely used as insulators in microelectronics due to their high dielectric strength, mechanical robustness, and thermal stability. However, organic–inorganic composite systems suffer from undesirable performance and accelerated degradation due to leakage current (JTot). Unfortunately, the underlying mechanism of JTot and its components (e.g., ionic and electronic constituents) are inadequately understood, particularly in extreme use conditions (e.g., high humidity and temperature). In this study, we use numerical simulation and experimental JTot data (in amorphous epoxy polymer with silica fillers) to (i) unify the electrostatic model for JTot in composite polymers, (ii) illustrate that the early part of JTot (i.e., external current) is primarily due to the image charge associated with ion transport/ localization (Jion) near the metallic contacts, (iii) demonstrate that the accumulated counter-ions reduce the barrier for electronic charge injection (by band bending) and facilitate electronic injection from the metals (Jelec), and (iv) provide an algorithm for the in situ ion transport characterization of composite insulators by exploiting Jion. This work provides new insights regarding the leakage current mechanism and how it can be used as a probe into the complex transport mechanisms of the composite material.