Charge Injection at Metal-Polymer Interfaces a First-Principles Study

Abstract

The long term insulating behavior of polymers critically depend on the polymer-metal interfaces. Injection of charged particles (electrons/holes), from the electrodes (metals) to the dielectric at these interfaces are precursors to dielectric aging which culminates in breakdown of the dielectric. The probability of this charge injection is decided by the energy difference between the fermi level of the electrode and the edges of valence and conduction bands of the dielectric. For a given polymer-metal interface, this primarily alignment depends on the dipole moments created by various features at the interface. Here, using calculations based on density functional theory (DFT), we look closely at some common interface features developed during physical vapor deposition of Al and Au on poly-propylene (PP), poly-styrene (PS), and Polyethylene Terephthalate (PET), surfaces and their effects on the charge injection behavior. On comparing our results with the experimental values, we see that adding defects on the interface bring the computed values of charge injection barriers closer to the experimental values, suggesting the presence of various defects at the interface. We also observe that by controlling the concentration of interface defects, we can align the fermi-level of the metal in the middle of the bandgap of the dielectric which potentially minimizes charge injection and impede the process of aging and breakdown.