Preparation And Performance Studies Of Tunable Microwave Electromagnetic Materials

With the improvement of the modern science and technology, and the demand of tunable microwave devices, the material has tunable microwave electromagnetic properties, such as the ferroelectric material and ferromagnetic material, has become an important research topic. Barium strontium titanate dielectric ceramic, which is a very important microwave material, has a large dielectric constant, low dielectric loss, good dielectric tunability and other advantage. So, it has a broad prospect in the phase shifter, reconfigurable antenna, and other tunable microwave devices. The microwave soft magnetic thin film is an important material in today’s microwave integrated circuits which can effectively improve the micro magnetic inductance, can be manufactured circulator using its gyromagnetism, and can be made tunable antennas using its magnetic permeability. The value of f_FMR can be decided by saturation magnetization 4 Ms and the in-plane uniaxial anisotropy field HK of the magnetic thin film. The in-plane uniaxial anisotropy field HK as a extrinsic parameters is more sensitive, and it can be influenced by the preparation conditions, defects and so on. It is easier to be increased by 1-2 orders of magnitude. So more and more researchs has been focused on improving the uniaxial anisotropy field of the soft magnetic thin film. The main work of this paper is:Firstly, we prepared Bax Sr_1-xTiO₃ ceramics, which has different Ba / Sr ratiowith 0/1, 1/9, 2/8, 2.5/7.5, 3/7, 3.25/6.75, 3.5/6.5, 4/6,4.25/5.75, 4.5/5.5, with solid state reaction. The effects of different Ba / Sr ratio on the the microstructure and dielectric properties of Bax Sr_1-xTiO₃ ceramic material was investigated. We can see that, with the increase of the content of Ba, the microwave dielectric constant increases from 286 to 1305, and the dielectric loss increases from 0.624×10^-3to 2.426×10-3, the tunability increases to 30 percent.Secondly, we prepared BST-based microwave composite ceramics, which contain BST, BST doped with 30 percent and 60 percent, BST doped with 60 percent and 0.2 percent Mn O₂ composite ceramics. And we studied the microstructures and dielectric properties of different composite ceramics. We can see that, with the increase of Mg O content, the dielectric constant of the sample reduced from 1605 to 84.7, the dielectric loss increased from 2.49 × 10^-3to 4.46 × 10-3. And after doping Mn O2, the dielectric constant reduced to 81.4, while the electrical loss also declined to 4.06×10^-3. We also detected the reason of this through XRD and SEM. It is revealed that the Mg²⁺ ions are able to enter the lattice of BST, lead to the reducing of the dielectric constant, the increase of the dielectric loss, and the decrease of the dielectric tunability. MnO₂ with lower melting temperature would be enriched around the Mg O grain boundary. As a result, it gave rise to reduced grain size of Mg O, hindered the entrance of Mg²⁺ into BST, reduced the current leakage and dielectric loss, and enhanced tunability.Lastly, Fe_0.7Co_0.3B films with 100 nm were deposited on（100）-oriented Si substrates by CGS.The X-ray absorption spectrum（XAS） revealed that the decrease in the saturation magnetization 4πMS from 16.3 to 13.5 k G for the CGS-Fe_0.7Co_0.3B films can be attributed to the hybridization between Fe and B atoms. A considerable increase in uniaxial magnetic anisotropy fields HK from 180.6 to 295.5 Oe dominates the increase in f FMR from 4.82 to 5.62 GHz.