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Study on Doping Effects of BST Ceramics and Preparation of BST Thin Film

Author: WangCheng
Tutor: HuZuoQi
School: Huazhong University of Science and Technology
Course: Microelectronics and Solid State Electronics
Keywords: Barium strontium titanate Doping effects Dielectric constant Microwave loss Tunability Ferroelectric phase shifer
CLC: TB383.2
Type: Master's thesis
Year: 2011
Downloads: 80
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Abstract


Barium strontium titanate（BaxSr1-xTiO3） is one of the most promising materials in making electronic tunable devices such as microwave ferroelectic phase shifer. However, pure BST materials with high tunability also exhibits high permitivity and high microwave loss,which make it difficult to satisfy the microwave impedance matching.In this paper, we have investigated the doping effects of BST ceramics and fabricated BST ceramics and thin film with high tunability、low loss、moderate permitivity,which is expected in designing the ferroelectric phase shifer.In this paper, the doping effects of BST materials including both low barium content （x=0.40） and high barium content（x=0.55） were investigated with using the modification idea which combnies“composite doping”and“substitute doping”.For the BST of low barium content （x=0.40）, La2O3 dopoed Ba0.40Sr0.60TiO3/MgO composite ceramics were prepared. The results of microstructure analysis show that BST and MgO crystal grains coexist in a composite ceramics,and La3+ have entered BST lattices which forming the effect of“substitute doping”;The measurement results of dielectric properties repressented: La2O3 doping can reduce the microwave loss evidently, The 0.5wt%La2O3 doped sample has the best properties: dielectric constantε=91.5, tanδ=0.0008 （10GHz）, and the tunability =17.6%（2KV/mm10KHz）.For the BST of high barium content （x=0.55）, La2O3 dopoed Ba0.55Sr0.45TiO3 /Mg2TiO4 composite ceramic were prepared. The results of microstructure analysis show that La3+ enter BST lattices when the quality content of La2O3 reach to 1.2wt%,and La3+ doped sample can prevent chemical valence Ti in Ba0.55Sr0.45TiO3 /Mg2TiO4 composite system from +4 to +3. Their measurement results of dielectric properties repressented: Mg2TiO4 and La2O3 doping can reduce the dielectric constant and microwave loss separately. The 1.2wt%La2O3 sample has the best properties: dielectric constantε=52, tanδ=0.001 （10GHz）, and the tunability 13.4%（3KV/mm,10KHz）,.BST thin film was prepared by RF magnetron sputtering with La2O3 dopoed Ba0.40Sr0.60TiO3/MgO composite ceramic target. The microstructure of the film exhibits fully grown BST grains with well-defined grain boundaries and crack-free smooth surface; dielectric properties dielectric repressented as follows: constantε=176.5, tanδ=0.001 （100KHz）, and the tunability 18.1%.

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