Measurement of Microwave Dielectric Properties of (Sr,Ba)Nb2O6 Thin Films

(001) oriented (Sr,Ba)Nb₂O₆ (SBN) thin films were deposited on MgO (001) single crystal substrates by the pulsed laser deposition method. Structural properties of SBN films were investigated using X-ray diffractometer. The microwave dielectric properties of SBN films were examined by calculating the scattering parameter obtained using a HP 8510C vector network analyzer with the frequency range 0.5–20 GHz at room temperature under the dc bias field of 0–80 kV/cm for interdigital capacitors (IDT) and coplanar waveguide (CPW) device based on SBN/MgO layer structure. Thick metal electrode patterns were fabricated by dc sputtering deposition, photolithography and etching process. The IDT device based on (001) oriented SBN films exhibited about 40% capacitance tunability with an electric field change of 80 kV/cm at room temperature, and the dielectric quality factor was about 20 at 12 GHz with no dc bias.     

ENHANCED TUNABILITY AND RELAXOR CHARACTERISTICS IN CALCIUM SUBSTITUTED BARIUM ZIRCONIUM TITANATE THIN FILMS

ABSTRACT

Thin films of BaZr_0.25Ti_0.75O₃ in which Ba^{2 +} is partially substituted by Ca^{2 +} are prepared by a sol-gel method. Phases and dielectric properties of the films are studied.The crystal structure of BaZr_0.25Ti_0.75O₃ is cubic and does not change with Ca substitution upto x = 0.25 in Ba_1-xCa_xZr_0.25Ti_0.75O₃. A change from a normal to relaxor behavior is observed for x = 0.20 as indicated by a change in the frequency of dielectric maxima with temperature and other parameters.The dielectric constant and transition temperatures are found to increase with increasing Ca substitution. A tunabilty of 71%, much higher than reported in literature for this material, is observed for x = 0.1 i.e for Ba_0.9Ca_0.1Zr_0.25Ti_0.75O₃.     

Structural and Electrical Properties of Ba(ZrxTi1-x)O3 Films Prepared by RF-magnetron Sputtering Using Metal Targets

Ba(Zr_xTi_1-x)O₃ (BZT) thin films with different Zr contents were deposited on (100)MgO and (100)Pt/(100)MgO substrates by RF-magnetron sputtering using metal targets. The BZT thin films had a single perovskite phase with only (001)/(100) orientation. In all cases, the ratio of Ba/Ti was stoichiometry and BZT films possess a dense microstructure. The grain size was decreased and BZT thin films showed ferroelectric-to-paraelectric properties with increasing Zr content. At room temperature, the tunability of nearly 30% was achieved at 1 MHz; meanwhile, a relatively low dielectric loss was obtained. These results indicated that we succeeded in depositing high-quality and potential tunable ferroelectrics.     

纳米晶Ba（Zr0．2Ti0．8）O3薄膜的外延生长与介电特性

用脉冲激光沉积工艺在半导体（001）SrTiO3：ω（Nb）=1．0％单晶基片上,外延生长出Ba（Zr0.2Ti0.8）O3（简称BZT）介电薄膜．在650℃原位退火10min,薄膜为（001）外延生长的晶粒．薄膜的晶化特征与表面形貌用薄膜X-ray衍射仪和原子力显微镜测量完成．BZT薄膜（002）峰的半峰宽只有0．72°,说明薄膜晶化良好;薄膜的平均晶粒为90nm,表面均方根粗糙度为4．3nm,说明薄膜表面平整．在室温、100kHz和500kV／cm条件下,BZT的最大介电常数和调谐百分率分别达到317和65％．     

Dielectric tunable properties of BaTi<Subscript>4</Subscript>O<Subscript>9</Subscript>-doped Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> microwave composite ceramics

BaTi₄O₉-doped Ba_0.6Sr_0.4TiO₃ (BST) composite ceramics were prepared by the conventional solid-state reaction and their structure, dielectric nonlinear characteristics and microwave dielectric properties were investigated. The secondary phase of the orthorhombic structure Ba₄Ti₁₃O₃₀ is formed among BST composite ceramics with the increase of BaTi₄O₉. At the same time, a duplex or bimodal grains size distribution shows fine grains in a coarse grain matrix. The degree of frequency dispersion of dielectric permittivity below T _m is increased initially and then decreased with respect to BaTi₄O₉. As the BaTi₄O₉ content increases, the tunability of composite ceramics decreases, while the Q value increases. Interestingly, 70 wt% BaTi₄O₉-doped BST has a tunability ∼4.0% (under 30 kV/cm biasing) versus a permittivity ∼68 and quality factor ∼134.1 (at ∼3.2 GHz). Supported by the Ministry of Science and Technology of China through 973-project (Grant No. 2009CB623302), the Cultivation Fund of the Key Scientific and Technical Innovation Project, Ministry of Education of China (Grant No.707024), Shanghai Committee of Science and Technology (Grant No. 07DZ22302), and Shanghai Foundation Project under 06JC14070     

The anomalous increase in tunability in Ba0.55Sr0.45TiO3-MgO-Mg2SiO4 composite ceramics

The Ba_0.55Sr_0.45TiO₃–Mg₂SiO₄–MgO composite ceramics were prepared via solid-stated method and the dielectric tunable properties of composite ceramics were investigated. With the increase in dielectrics content, the tunability of composites ceramics increased abnormally first and then decreased, while the anharmonic coefficient increased monotonously. A simple 3D Finite Element model was developed to simulate the dielectric response and an anomalous increase in tunability when increasing the dielectrics content in composites was obtained. The simulation indicated that adding dielectrics into ferroelectrics causes the redistribution of the electric field. Increasing dielectrics content, the average electric field strength in the enhanced area of ferroelectrics increases, which lead to the increase in the tunability. The abnormal increase in tunability originates from the enhancement of the electric field on a fraction of the ferroelectrics around dielectrics.     

Tunable Dielectric Characteristics of 0.9Pb(Fe<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>)O<Subscript>3</Subscript>/0.1CaTiO<Subscript>3</Subscript>

Tunable dielectric characteristics of 0.9Pb(Fe_1/2Nb_1/2)O₃/0.1CaTiO₃ relaxor ferroelectric ceramics were investigated as the function of DC bias field and temperature. High tunability (more than 20%) was obtained in the present ceramics under a relatively weak DC bias field (1.4 kV/cm). The value of tunability changed from negative to positive with increasing DC field. For the simulation of the dielectric constant under DC bias field, modified model needs to be constructed for the relaxor ferroelectrics. The dielectric constant curve as a function of temperature without and under DC field was well fitted using the equation of diffuse phase transition. The lower ε_max, higher T_max and higher diffuseness parameter under DC field were observed and only the lower ε_max contributed to positive tunability.     

新型阶梯形可调谐光滤波器的优化设计

针对阶梯形可调谐光滤波器(LTOF)的结构特点,建立LTOF多光束干涉的理论模型,从理论上对其输出性能和调谐性能进行优化设计。结果表明：通过对输出谱、峰值功率、邻道串扰及3dB带宽进行数值分析和比较,得到了最优级联级数和分光比;设计出峰值损耗低于10dB,邻道串扰低于-12dB和3dB带宽低于5nm的器件,其最优级联级数和分光比分别为20和0．85。提出增大电极长度至1．4倍来覆盖整个58nm的自由频谱区(FSR)的设计方案,实现了连续调谐。     

Cd掺杂BZCN薄膜的制备及其介电性能

用射频磁控溅射法,在Pt/Si基片上制备了立方烧绿石结构的Cd掺杂Bi1.5Zn0.7Cd0.3Nb1.5O7(BZCN)薄膜。研究了衬底温度对薄膜结构、表面形貌以及介电性能的影响。结果表明,沉积温度为600℃,退火温度为700℃制备的薄膜,在测试频率为100 kHz,测试电场强度为1.33×106 V/cm的条件下,介电可调率达到11.8%,tanδ小于0.004 2。     

Ba_(0.6)Sr_(0.4)TiO_3/ZnNb_2O_6复相陶瓷的显微结构和介电性能

采用传统电子陶瓷工艺制备了Ba_(0.6)Sr_(0.4)TiO_3/ZnNb_2O_6(BSTZ)复相陶瓷,研究了ZnNb_2O_6含量对BSTZ陶瓷结构和介电性能的影响规律.结果表明,BSTZ复相陶瓷可在较低温度下烧结成瓷;陶瓷中除了Ba_(0.6)Sr_(0.4)TiO_3和ZnNb_2O_6两种主晶相,还有新相BaNb_(3.6)O_(10)生成;陶瓷的介电常数和介电损耗均随ZnNb2O6含量的增加而降低;当x(ZnNb_2O_6)=0.6(摩尔比)时,复相陶瓷在微波下的介电常数为74,介电损耗为0.043,可调性可达10.54%(1.0 kV/mm).