Side-chain modification to boost the dielectric constant of polymers: toward high-k material synthesis and application in low-voltage operating printed electronics†

Polymers with high dielectric constants (k) are favorable for various electronic applications, including high-energy-density capacitors and low-voltage-operating organic thin-film transistors (OTFTs). However, conventional high-k polymer-based materials face difficulties in these electronic applications in general environments owing to their crystalline state or phase separation/imbalance caused by inorganic fillers. In this study, we propose a method to increase the k values of amorphous intrinsic polymers through side-chain modifications. The value of k depends on the polarizability of the material, which is directly related to the dipole characteristics that can be aligned under an electric field. As polymers have carbon-based covalent bonds, these characteristics are not noticeable. Therefore, we introduced two side-chain groups that can create strong dipole arrangements under electric fields, observing high k values (>6) when the dipole moment of the monomer was high. The insulating features of the new polymers are comparable to those of poly(methyl methacrylate), despite their high k values. The new polymers were successfully applied as gate dielectrics for OTFTs operating at 3 V and in integrated logic devices. The devices had excellent field-effect mobility (≈1.90 cm² V⁻¹ s⁻¹) and operational stability under a bias stress test.