Atomic layer deposition coated polymer films with enhanced high-temperature dielectric strength suitable for film capacitors

Although polymer film capacitors are widely used in power electronic systems, their high-temperature performance deterioration severely limits their further application. This work shows conclusively that ultrathin alumina coating by atomic layer deposition (ALD) can significantly improve the thermal stability and capacitance stability of polypropylene (PP) films at temperatures above 140 ˚C. We demonstrate for the first time the ALD coating enhancement on breakdown strength (>600 V/μm) and elastic modulus of both crystalline PP and amorphous polyetherimide (PEI) at higher temperatures. The discharged energy density of ALD alumina-coated PP and PEI films reached 4.1 J/cm3 at 140 ℃, 2.6 J/cm3 at 150 ˚C, respectively, which is much higher than uncoated films. The finite element simulation also manifests the consistency in dielectric strength enhancement that may be attributed to the increased elastic modulus due to the alumina coating. This new perspective provides an effective pathway to obtain ultrathin surface coating for dielectric polymer films with enhanced dielectric strength, elastic modulus, and thermal stability promising higher temperature application.