Development of porous COP-ceramic composites for application as low-relative-permittivity, low-dielectric-loss...

Rapid advancements in communication technologies, such as the onset of 5G systems and the anticipated arrival of 6G systems, have increased the demand for materials with low relative permittivity ([Formula: see text]) and dissipation factor (tanδ) to enable stable, low-power communication at higher frequencies. In this study, cycloolefin polymer (COP)-based composites containing an alumina (Al₂O₃) or aluminum nitride (AlN) filler were subjected to foaming by supercritical CO₂ to introduce porosity, then evaluated as candidates for low-[Formula: see text] , low-tanδ substrates. Their dielectric properties were evaluated over a large frequency range of up to ~ 120 GHz using the balanced-type circular disk resonator method. The results demonstrated that porosity effectively reduced [Formula: see text] and tanδ without compromising the thermal properties; in particular, the COP-AlN composites exhibited [Formula: see text] and tanδ values below 2.0 and 1 × 10^-3, respectively. Furthermore, the [Formula: see text] trend was consistent with effective medium theories, specifically the Maxwell-Garnett and Bruggeman models. Additional analyses of the thermal expansion and conductivities of the composites revealed enhanced compatibility with copper conductors, supporting the viability of these composites for next-generation communication devices.