Polarization Analysis and Humidity Dependence of Dielectric Properties of Aromatic and Semialicyclic Polyimides Measured at 10 GHz

High Resolution Image Download MS PowerPoint Slide In this study, dielectric constants ( D k ) and dissipation factors ( D f ) of 15 types of polyimides (PIs), including wholly aromatic, semialicyclic, partially fluorinated, and perfluorinated PIs, were measured in the transverse electric (TE 011 ) mode at a frequency of 10 GHz and analyzed based on their chemical structures and the dominant factors of dielectric polarization per unit volume ( P t ). The relationships among the dipolar orientational ( P d ) and electronic ( P e ) polarizations and dielectric properties ( D k and D f ) were quantitatively investigated. Although a systematic correlation between the structure and D f of PIs has not yet been established, we found that the D f of PIs is anisotropic and linearly proportional to P d in the in-plane direction, which can be estimated from the D k and in-plane refractive index ( n TE ) at 1310 nm. This could be related to the bidirectional relationship between the real ( D k ) and imaginary ( D f ) parts of the relative permittivity. Furthermore, the D k and D f of all PIs increased linearly with respect to the relative humidity (RH) of the measurement environment, and their slopes ( h Dk and h Df ), i.e., the RH sensitivities of D k and D f, showed a proportional relationship with a high correlation coefficient ( R 2 = 0.986). The weight fraction of polar imide and ester groups (Polar %) and the hydrophobicity of PIs, which are closely related to the fluorine content ( F %), are essential factors in determining the values of D k, D f, h Dk, and h Df . These relationships are crucial for developing low-dielectric PI materials exhibiting low D k and D f values, as well as reduced sensitivity to humidity.