Controlling the temperature coefficient of dielectric constant of polyphenylene oxide-based composites

Abstract

The temperature coefficient of dielectric constant (τε) is a crucial parameter for assessing the performance stability of microwave devices operating under varying temperature conditions. In this study, polyphenylene oxide (PPO) resin was utilized as the matrix and six types of ceramics with distinct temperature coefficients of dielectric constant were employed as fillers. Six PPO-based composites were fabricated through twin-screw extrusion combined with hot pressing route. The dielectric properties of the ceramics and their influence on the dielectric properties of the composites, particularly the τε, were systematically investigated. The results revealed that all six types of composites exhibited dense structures and uniform filler distribution, with a relative density exceeding 98.0 % and a water absorption below 0.1 %. The dielectric constant and its temperature coefficient of the fillers had a more pronounced effect on the dielectric properties of the composites, compared to dielectric loss. The dielectric constants of the six types of composites aligned well with the theoretical values predicted by the effective medium theory. Reaching up to 9.7 (at 10 GHz). The dielectric loss ranged from 1.0 × 10−3 to 3.0 × 10−3. Notably, the PPO/Mg0.95Ca0.05TiO3 composite substrate with a filler ratio of 40 vol% exhibited exceptional dielectric properties: εr = 6.8, tgδ = 1.4 × 10−3, τε = −8.6 ppm/°C, highlighting its significant advantages for communication applications under varying temperature conditions.