High-frequency electrical properties of silver thick films measured by dielectric resonator method

The electrical properties of silver films, prepared using a low-curing-temperature metallo-organic-decomposition (MOD) paste and a high-temperature silver paste screen-printed on polished and nonpolished alumina substrates, at microwave frequency were characterized in this study. Surface resistance and effective conductivity of the silver films at microwave frequency (approximately 4 GHz) were evaluated using the TE₀₁₁ mode of the resonator cavities method. Devices of T-type resonator circuits were fabricated to determine the simulated and measured Q-values and to evaluate the effects of silver films and the surrounding substrate. The surface roughness of the fired films printed on nonpolished Al₂O₃ substrate is slightly less than those on polished substrate, because the surface energy of the nonpolished alumina (29.81 mN/m) is slightly less than that of the polished alumina (36.69 mN/m). The calculated effective conductivities at 4.3 GHz are slightly less than the DC conductivities of the films. Moreover, the films prepared using the high temperature silver paste have higher electrical conductivity ranging from 4.08 × 10⁷ to 4.13 × 10 ⁷ S/m, since the high-temperature firing process leads to an improved connectivity of the silver particles. The results indicate that the films screen-printed on the polished substrate have a higher Q and a lower ΔQ value than those of films that are screen-printed on the nonpolished substrate. For the silver films prepared using the high-temperature silver paste, both the Q and ΔQ values were the highest among the films studied, which is consistent with the observation of the dense microstructure of the silver film and the interfacial reaction between the glass in the film and the substrate as a result of high firing temperature.