Effect of PTFE, PET, and PFA on the microwave dielectric properties of H3BO3 ceramics

The (1-x)H3BO3-xPTFE, (1-x)H3BO3-xPET and (1-x)H3BO3-xPFA (x = 0.0–0.5) polymer-ceramics prepared by conventional solid phase method for microwave substrate application is presented in this work. As x value increases from 0.0 to 0.5, the XRD, Raman and SEM results shows that two coexisting phases (H3BO3 and PTFE/PET/PFA) are present in the polymer-ceramics, and no other heterogeneous phases are generated. For the microwave dielectric properties, the polymer-ceramic systems are predicted by using different theoretical methods and compared with some experimental data. The εr, τƒ and Q׃ values are applied to the logarithmic, parallel and series mixing law, respectively. Therein, the relative permittivity (εr) value declines from 2.83 to 2.48, and the dielectric loss (tanδ) of the three systems basically fluctuated in the range of 0.000807–0.004580. Considering the effect of densities and H3BO3 intrinsic properties, the (1-x)H3BO3-xPTFE (x = 0.5) polymer-ceramics sintered at 110 °C for 1 h has the best dielectric properties: εr of ∼2.48, Q׃ of ∼7747 GHz at 15.6 GHz and τƒ of ∼ −19 ppm/°C. On the other hand, the 0.5H3BO3-0.5PTFE, 0.5H3BO3-0.5PET and 0.5H3BO3-0.5PFA polymer-ceramics are selected for the hydrolysis experiment (24–384 h). Wherein, compared with the pure H3BO3 ceramics, the Q׃ value and mass of these polymer-ceramic samples don't change significantly before and after the hydrolysis experiment, and there are no the appearance of the powder dropping. Therefore, these new-types ultra-low temperature sintering H3BO3-based polymer-ceramics can be considered as a ideal candidate substrate material in the 5G era.