【作者】 王成；

【导师】 胡作启；

【作者基本信息】 华中科技大学 ， 微电子学与固体电子学， 2011， 硕士

【摘要】 钛酸锶钡(Ba_xSr_1-xTiO₃,简称BST)在研制电可调谐器件（如微波铁电移相器）具有巨大的应用潜力。但纯BST在调谐率较高时,介电常数较高,损耗也比较大,还不能完全满足制备微波铁电移相器的要求。本论文通过对BST进行掺杂改性研究,期望研制出高调谐率、低损耗、介电常数适中的优良综合性能的BST块体及其薄膜材料,最终能满足器件设计的要求。本论文采用“复合掺杂”和“替位掺杂”相结合的掺杂改性思路,分别对低钡（x=0.40）和高钡（x=0.55）两种BST材料进行了掺杂改性研究。对于低钡BST材料,实验制备了La₂O₃掺杂的Ba_0.4Sr_0.6TiO₃/MgO的复合陶瓷材料,微观性能测试结果显示:样品中BST与MgO形成了较良好的复合结构,La³⁺进入BST晶格形成了“替位掺杂”效应;电性能测试表明:微量La₂O₃掺杂能有效地降低BST材料的微波介电损耗,0.5wt%La₂O₃掺杂量的样品在10GHz频率下测试的介电常数为ε=91.5,介电损耗为tanδ=8×10^-4;低频调谐率为17.6% （2KV/mm）。对于高钡BST材料,实验制备了La₂O₃掺杂的Ba_0.55Sr_0.45TiO₃/Mg₂TiO₄的复合陶瓷材料,微观结构分析结果表明:当La₂O₃的掺入量为1.2wt%时,La³⁺进入BST晶格,且其过程抑制了Ba_0.55Sr_0.45TiO₃/ Mg₂TiO₄复合材料体系中的Ti从+4向+3价转化;电性能测试结果表明:Mg₂TiO₄和La₂O₃的掺入能分别较明显地降低介电常数和微波介电损耗,当La₂O₃掺入量为1.2wt%时其微波（f=10GHz）介电常数为ε=52,介电损耗tanδ=0.0011,低频下调谐率13.6%（3KV/mm）。将0.5wt%La₂O₃掺杂的Ba_0.4Sr_0.6TiO₃/MgO复合陶瓷材料加工成溅射靶材,利用磁控溅射法制备了BST薄膜材料。微观测试结果显示所制备的BST薄膜致密、无裂纹,低频下（f=100KHz）测试其常数ε=176.5,介电损耗tanδ=0.011,调谐率为18.1%。更多还原

【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 Ba_0.55Sr_0.45TiO₃ /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 Ba_0.55Sr_0.45TiO₃ /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%.更多还原