Photocurable low-dielectric polyimide via acrylate side-chain engineering for 3D-printed RF applications

초록

Photopolymer-based 3D printing techniques such as digital light processing (DLP) enable the fabrication of complex geometries with high resolution, offering potential for next-generation radio frequency (RF) components. However, many reported photocurable resins for RF applications still show limited dielectric performance at GHz frequencies. Polyimide (PI) is an attractive candidate due to its thermomechanical properties, yet some reported 3D-printable PI systems require organic solvents, suffer from significant volumetric shrinkage, and exhibit insufficient dielectric characteristics for high-frequency applications. Here, a side-chain engineering strategy is presented that incorporates photocurable acrylate groups into the PI backbone, enabling solvent-free formulations compatible with DLP processing while suppressing in-plane shrinkage to below 0.1%. Systematic control of side-chain density reduces polar group density and forms a crosslinked network with suppressed dipolar relaxation, simultaneously achieving low Dk and Df and thermomechanical properties. The optimized formulation (PI-IA15-R) exhibited a Dk of 2.42 and a Df of 0.0078 at 28 GHz (2.67 and 0.0088 at 80 GHz), along with a dielectric strength of 157.7 kV/mm. DLP-printed antenna substrates demonstrate stable RF performance with a simulated maximum realized gain of 9.08 dBi and radiation efficiency of 94%, bridging molecular design and functional mmWave device fabrication.

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