Universally Correlating the High-Frequency Dielectric Properties with Structural Parameters of Polyimides with Diversified Functional Groups
Chia-Lo Chung, Yi-An Tsai, Yu Liu, Yu-Che Chen, Chi‐cheng Chiu, Wen‐Chang Chen, Yan‐Cheng Lin
Abstract
High Resolution Image Download MS PowerPoint Slide With the increasing demand for high-frequency signal transmission and chip miniaturization, conventional insulating materials face significant limitations. Among various low-loss materials, polyimide (PI) stands out for its excellent processability, stability, and diverse chemical structure. In this study, 54 PIs incorporating various functional groups, including ether, ester, fluorine, amide, and sulfone, were analyzed for their effects on the dielectric constant ( D k ) and dissipation factor ( D f ). A combination of theoretical simulation and experimental methods is adopted to investigate the dielectric behavior of PIs. Density functional theory (DFT) was employed to calculate the polarizability, while molecular dynamics (MD) simulations were used to evaluate realistic chain conformations and volumetric properties. The PI film’s refractive index is measured for calculating its electronic polarizability (α e ). The analysis further distinguishes between electronic and dipolar contributions to the DFT-calculated total polarizability (α t ). It examines their correlations to the D k and D f values across different frequencies, demonstrating the complementarity between the semitheoretical (α e ) and theoretical (α t ) methods. Based on local chain stiffness, a correction factor for the fraction of free volume (FFV) derived from MD simulations is proposed to enhance the predictive relationship between volumetric polarizabilities ( N α t or N α e ) and dielectric properties. Results show that at higher frequencies, the semitheoretical ( N α e ) and theoretical ( N α t ) regressions exhibit a better correlation, indicating that this FFV-modified regression parameter is more suitable for predicting dielectric properties in high-frequency systems. The combination of DFT and MD calculations can generate theoretical parameters for correlating the PI’s D k and D f values at high frequencies; the corresponding parameters are the ratio or product between volumetric total polarizability and free volume fraction, respectively. This study offers a comprehensive approach, combining structural modeling and frequency-dependent experimental validation to provide a predictive and practical framework for designing low-dielectric polymers for advanced electronic and communication applications.