Research On Microwave Properties Of The (Zn_1-xMg_x)₂SiO₄-based Ceramic Sintered At Low Temperature

With the development and utilization of microwave frequency, LTCC technology has beenproposed to prepare the laminated microwave devices for high-quality and high-speed transmission.Thus, the low dielectric constant microwave ceramics with desirable properties and low sinteringtemperature have become a hot research field. In this thesis, the (Zn_1-xMg_x)₂SiO₄-based ceramic hasbeen studied by means of XRD, SEM and the measurements of the density and dielectric properties tooptimize the microwave and sintering properties.（Zn0.8Mg0.2）2SiO4has been found to be an optimal composition in the (Zn_1-xMg_x)₂SiO₄system, andthe dielectric properties of （Zn0.8Mg0.2）2SiO4ceramic have been enhanced by ZrO₂doping. It has beenfound that （Zn0.8Mg0.2）2SiO4ceramic added with1.0wt%ZrO₂shows the highest density and bestdielectric properties: ρ=3.9g·cm-3, εr≈7, tan δ≈10-5（f=5MHz） as well as perfect microwaveproperties: r=6.35, Q f=9.33×104GHz, f=-57.9ppm/C when sintered at1350°C for3h.（Zn0.8Mg0.2）2SiO4-1.0wt%ZrO₂（ZMSZ） ceramic has high negative τf, which precludes itsimmediate use in practical applications. Hence various amounts of TiO₂have been added tocompensate the high negative fof the composite ceramic. The τfof the composites increases afteradding TiO₂and ZMSZ-9wt%TiO₂（ZMSZT）composite ceramic sintered at1240°C/3h exhibits a nearzero temperature coefficient of resonant frequency （τf=-0.87ppm/°C）. However, the sinteringtemperature of the ZMSZT ceramic is too high to co-firing with Ag/Cu.The sinter-ability of ZMSZT ceramic has been improved with B₂O₃or/and Li2O additions, thecorresponding composites can be sintered at a low sintering temperature. It has been found thatZMSZT ceramic with3wt%B₂O₃addition sintered at960°C/3h shows good microwave properties: r≈9.3, Q f≈2.8×104GHz, f≈6.3ppm/C. In order to further decrease the sintering temperature,1wt%B₂O₃+4wt%Li2O has been introduced to decrease the sintering temperature of ZMSZT to930°Cwith high density and better microwave properties: ρ=3.86g·cm-3, εr≈9.4, Q f≈3×104GHz, τf=-5.7ppm/°C. However, the properties of ZMSZT ceramic decline when added with3wt%B₂O₃+4wt%Li2O.Consequently,（Zn0.8Mg0.2）2SiO4-based ceramic can be utilized as LTCC materials successfully whendoped with suitable additions.