Thermally Robust Zirconia Nanorod/Polyimide Hybrid Films as a Highly Flexible Dielectric Material

In this study, a strategy for the fabrication of zirconia-polyimide (ZrO2-PI) nanohybrid films with high permittivity (high-k), thermal stability, and excellent mechanical properties has been developed. A colloidal suspension of ZrO2 nanorods was prepared using the facile microwave-hydrothermal treatment approach. The ZrO2-PI nanohybrid film was fabricated by casting an aqueous solution containing water-soluble poly(amic acid) ammonium salt (PAS) and water-dispersible ZrO2 nanorods followed by thermal imidization. Atomic force microscopy and scanning electron microscopy images indicated that the ZrO2 nanorods were uniformly dispersed in the PI matrix. Because of the high permittivity of the ZrO2 nanorods and good compatibility between polyimide and ZrO2 as well as the nanosize of ZrO2, the permittivity increased to 5.1 as the ZrO2 concentration reached 10% at 10 Hz, while the dielectric loss was as low as 0.05 at 10 Hz. The prepared ZrO2-PI nanohybrid films had excellent heat resistance with quite low coefficients of thermal expansion (CTE), as low as 16.3 ppm/K. The ZrO2-PI nanohybrid films have excellent thermal stability and good mechanical flexibility. Moreover, no distinct changes were observed for the PAS solution over a storage time of 3 months, after which the nanohybrid film could still be successfully synthesized by thermal imidization. In addition, the water uptake of the ZrO2-PI nanohybrid film was approximately 2.5% under 60% relative humidity. The high stability of the PAS precursor, good flexibility, enhanced permittivity, and low CTE behavior of the ZrO2-PI nanohybrid films could make this strategy attractive for the ecofriendly design of dielectric polymer nanohybrids as well as for the fabrication of nanohybrid films with potential applications in high charge-storage capacitors and organic field-effect transistors (OFETs) in the flexible electronics industry.