Research On Dielectric Properties Of K And Mg Codoped Bst Films

Barium strontium titanate(BST) film has developed into an important candidate material for tunable microwave devices due to its highly nonlinear dielectric response to an applied electric field. In this paper, K、Mg single doped and codoped hetero multilayer BST films which consist of STO film layers were fabricated using improved sol-gel method. The microstructure、surface morphology and dielectric properties were analyzed by XRD 、 SEM and C-V testing, and the doping methods and doping concentration of K and Mg were researched. The main results are as follows:Firstly, After adding the STO film, the(110) peak of BST film tend to right and the average grain size tend to small. The surface morphologies showed more uniform microstructure and the film reveal smoother and denser morphologies. The dielectric loss largely reduced and the integrated dielectric properties was improved significantly.Secondly, The 5mol% K and Mg single doped multilayer BST films were researched at different structures and the dielectric loss of doped BST films was obviously decreased. Under the structure of BST/STO/BST, the dielectric loss of 5mol% Mg doped multilayer BST film decreased to 0.02 at 10 V bias and the FOM was 18.1, while the 5mol% K doped multilayer BST film kept a relatively high tunability, which improved the FOM to 22.3. Under the structure of STO/BST/STO, the tunability of 5mol% Mg doped multilayer BST film slightly decreased and the value was 21.9, which devoted into a reduced dielectric properties. However, for the 5mol% K doped multilayer BST film, the dielectric tunability increase to 41.2% at 10 V bias and the dielectric loss decreased to 0.012, the FOM reached 34.3, respectively.Thirdly, The K and Mg codoped multilayer BST films under the structure of BST/STO/BST were innovatively researched, and the doping methods and doping concentration were also optimized. Compared to the single Mg doped BST film, the tunability of 5mol% K and Mg codoped multilayer BST film improved slightly and the FOM was 16.2. Keeping the total doping concentration of K and Mg was 5mol%, the 4mol% K and 1mol% Mg codoped film exhibited optimized dielectric properties, the dielectric tunability at 10 V bias increased to 51.7% and the dielectric loss decreased to 0.011, which make the FOM improve to 47. Keeping the K doping concentration was 1mol%, the high doping concentration of Mg will make the tunability decrease, at which the 3mol% Mg doping concentration codoped multilayer BST film exhibited better dielectric properties. The dielectric tunability and dielectric loss at 10 V bias were 40% and 0.011, with the FOM reached 36.4. Meanwhile, at the research of low doping concentration of K and Mg, the integrated dielectric properties largely improved when the doping concentration of K and Mg all was 2mol%. The tunability increased to 52.3% and the dielectric loss between 0.008 and 0.014, with the FOM as high as 65.4, which can fully metting the needs of tunable microwave applications.