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

Abstract

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 (TE011) 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.