Research On Barium Strontium Titanium Oxide Ceramics With Low Dielectric Constant, High Tunability

Barium strontium titanium oxide (BSTO) has great advantages andpotentiality in future fields of microwave and information. The advantages ofBSTO electro-optic phase shifters over ferrite phase shifters are higherpower-handling capacity, faster phase shifter speed, lower driven power, lowinsert losses, smaller and light structure. The purpose of my research is toobtain the BSTO ceramics with low dielectric constant, high tunability andlow loss, which could be used in phase shifters.Two methods are used in my work: doping oxides (including A positionsubstitution and adding oxides directly) and making BSTO thick films. TGG(Template Grain Growth) is used in the process of making thick films.Ba_0.5Sr_0.5TiO₃ is used as matrix. As a result, when 5 wt% MgO or Al₂O₃ isadded directly, BSTO ceramics with dielectric constant lower than 800,tunability higher than 15%, dielectric loss around 10^-3 are obtained. Theenhancement of tunability could be explained by both the anharmonic effectsof Ti-O and the soft mode theory. The results of XRD reveal that thick filmsmade by TGG obtain more than 70% {001} texture. Texture has an effect ondielectric properties which is under further study.Additionally, I have also started initial research on using sol-gel methodto make BSTO thin films.