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The miniaturization of electronic devices and power systems for capacitive energy storage under harsh environments requires scalable high-quality ultrathin high-temperature dielectric films. To meet the need, ultrasonic spray-coating (USC) can be used. Novel polyimides with a dipolar group, CF3 (F-PI), and all-organic composites with trace organic semiconductor can serve as models. These scalable high-quality ultrathin films (≈2.6 and ≈5.2 µm) are successfully fabricated via USC. The high quality of the films is evaluated from the micro-millimeter scale to the sub-millimeter and above. The high glass transition temperature Tg (≈340 °C) and concurrent large bandgap Eg (≈3.53 eV) induced by weak conjugation from considerable interchain distance (≈6.2 Å) enable F-PI to be an excellent matrix delivering a discharge energy density with 90% discharge efficiency Uη90 of 2.85 J cm-3 at 200 °C. Further, the incorporation of a trace organic semiconductor leads to a record Uη90 of ≈4.39 J cm-3 at 200 °C due to the markedly enhanced breakdown strength caused by deep charge traps of ≈2 eV. Also, a USC-fabricated multilayer F-PI foil capacitor with ≈85 nF (six layers) has good performance at 150 °C. These results confirm that USC is an excellent technology to fabricate high-quality ultrathin dielectric films and capacitors.
Ren et al. (Mon,) studied this question.