Research Of Dielectric Properties And Phase Structure Characteristics Of K And Mg Alternately Doping BST Films

Barium strontium titanate ferroelectric film (Ba0.6Sr0.4TiO3, BST) is a newgeneration of microwave tuning material, which has a broad application and importantresearch significance. The effect of phase structure characteristics and dielectricproperties of alternately potassium (K) and magnesium (Mg) doping BST films werefocused on in this paper. The K doping, Mg doping, K/Mg alternately and Mg/Kalternately doping BST films were prepared by the improved sol-gel mothod. The phasestructure was analyzed by XRD, and the research of the ferroelectric-paraelectrictemperature was done. Then, the surface chemistry state and surface morphology ofdifferent doped concentration were compared. In the end, the influence of alternatelydoping on dielectric constant, tunability, FOM and other dielectric performanceparameters were analyzed and tested. The main contents of the thesis are summarized asfollows.Firstly, the phase structure characteristics of K and Mg alternately doping BSTfilms were researched. The results show that both of the single and alternately doping ofK and Mg contribute to the formation of perovkite structure, the intensity of perovkitestructure (110) characteristic peak was reinforced. The peak position was biased to thedirection of lower2θ, lattice constant becomed larger, half high width was broadened,corresponding to the smaller grain size and dielectric loss. When K was doped, K+mainly comes into point A to replace Sr2+, while Mg2+mainly comes into point B toreplace Ti4+as Mg was doped. Compared to undoping films, the test results of dielectricand temperature characteristics shows that both the single and alternately doping with Kand Mg make the films show good temperature characteristic, alternately doping hasbetter effect. Ferroelectric-paraelectric phenomenon of the films didn’t appear obviouslyduring-50~100C, and the dielectric constant changed slightly.Secondly, compared to single doping films, the analysis of XPS, SEM and AFMshows that alternately doping has obvious advantages in the formation of perovkitestructure and reduce of dielectric loss. The alternately doping films were smoothwithout any shrinkage cavity, which reflects the advantage of alternately doping, and can be proved by dielectric properties test.Thirdly, the dielectric properties of BST films with different doping mothods,different doping concentration and different test frequencys were researched. Thealternately doping can balance the high tuning of K doping and the low loss of Mgdoping. The films with perpect competitive dielectric properties can be obtained whenthe concentration of K/Mg alternately doping was10mol%, the dielectric constant wasmoderate, the voltage between-40~40V, the loss lower than0.011, the tunability was50%, and the FOM can reach55.6, which agree well with XRD and XPS testing results.The6layers alternately doping BST films can achieve good frequency stability.Furthmore, the phase structure characteristics and dielectric properties of alternatelydoping BST films were greatly influenced by the doping elements in the first layer.