Characterization of High Temperature Polymer Thin Films for Power Conditioning Capacitors

摘要

Capacitor dielectrics that can operate above 150 deg C are needed for power electronics in military propulsion and weapons systems. This report characterized and compares two high temperature polymer film capacitor candidates, poly(ether imide) (PEI) and poly(ether ether ketone) (PEEK), with poly(phenylene sulfide) (PPS) and biaxially oriented polypropylene (BOPP), which offer limited performance at high temperature. Breakdown strength at room temperature was about 320 MV/m for PEEK, 500 MV/m for PPS and PEI, and 720 MV/m for BOPP. At 150 deg C, breakdown strength for PEI decreased about 16% and about 13% for PEEK, while PPS remained unchanged. BOPP's maximum test temperature was 100 deg C, at which breakdown strength decreased by about 11%. Dielectric loss measurements suggest PPS has greater electrical conductivity at 200 deg C than PEEK or PEI, and PEI has a lower loss than PEEK at temperatures above 150 deg C and frequencies higher than 1 kHz. The low E-field conductivity for PPS was 6.90x10(-14) S/m at 165 deg C and 1.72x10(-11) S/m at 200 deg C; the manufacturer listed room temperature conductivity as 2x10(-16) S/m. The effect of conductivity on the temperature rise of the capacitors was analyzed. More measurements are needed to determine the conductivity of PEEK and PEI. Based on the measured data for breakdown strength and dielectric properties, PEI appears to be the better candidate.