SiO₂ Microwave Dielectric Materials

The preparation, phase constitution, microstructure and microwave dielectric properties of SiO2 low-dielectric-constant microwave dielectric materials were investigated, together with the effects of the structure and microstrucure on the microwave dielectric properties.Dense SiO2 amorphous bulks were prepared by different approaches, and the microwave dielectric properties were investigated. For SiO2 amorphous bulks prepared by solid state sintering, the dielectric constant (εr) and Qf value increasd with increasing the sintering time, while the temperature coefficient of resonant frequency (τf) decreased. The optimal properties with lowεr of 3.72, high Qf value of 44,300 GHz and lowτf of-14.4 ppm/℃were achieved when sintered at 1100℃for 5 hours. SiO2 amorphous bulks prepared by spark plasma sintering and melting method showed near-fully density, and the microwave dielectric properties were further improved, as listed below:εr= 3.90, Qf= 63,500 GHz,τf=-5.7 ppm/℃for spark plasma sintering, andεr= 3.83, Qf= 122,100 GHz,τf=-8.3 ppm/℃for melting method.Dense SiO2 ceramics with cristobalite phase were prepared by the solid state sintering, and the microwave dielectric properties were evaluated. As the sintering temperature increased, the dielectric constant (εr) and temperature coefficient of resonant frequency (τf) did not change much, while the Qf value increased significantly, and it was due to the increasing grain size. The optimized microwave dielectric properties withεr= 3.81, Qf= 80,400 GHz andτf=-16.1 ppm/℃were obtained for the cristobalite ceramics sintered at 1650℃for 3 hours.