Achieving high breakdown strength and figure of merit of Ba0.6Sr0.4TiO3 films through coating a Y3Fe5O12 layer

Low tunability and figure of merit significantly limited the application of Ba_0.6Sr_0.4TiO₃ (BST) ferroelectric film, which originates from the low electric breakdown strength and high dielectric loss of BST layer. Garnet structured Y₃Fe₅O₁₂ (YIG) exhibits the merits of good microwave dielectric property and a much high resistivity, which are helpful for enhancing the breakdown strength and suppressing the dielectric loss. In this work, Y₃Fe₅O₁₂/Ba_0.6Sr_0.4TiO₃ (YIG/BST) composite films were fabricated via chemical solution deposition method. The composite films exhibited a low dielectric loss (0.006) and an almost frequency independent dielectric constant in a frequency range from 10 kHz to 1 MHz. The electric breakdown strength was significantly enhanced from less than 400 kV/cm to around 800 kV/cm through coating a YIG layer, causing an excellent tunability of 72.84% and an ultra-high figure of merit (FOM=118) at 800 kV/cm in YIG/BST film. It is physically clarified that the conduction loss plays an important role in BST film while the intrinsic loss is the dominate factor for the YIG/BST composite films.     

稀土掺杂对钛酸锶钡光催化的影响

以溶胶-凝胶法制备钛酸锶钡,研究了制备条件及稀土掺杂对光催化影响。用大红染料模拟废水中难降解的有机物,以大红染料脱色率的变化来表征催化剂BST的光催化性能。结果表明,离子掺杂对大红染料的降解效果比钛酸锶钡的降解效果有所提高。掺入镧离子时降解率可达85％,提高60％;掺入钇离子时降解率可达65％,提高40％;两种离子掺杂时降解率可达70％,提高45％。     

钛酸锶钡(BST)薄膜SOL-GEL制备方法研究

利用碳酸盐代替部分醇盐，探讨了采用Sol-Gel技术制备Ba1-xSrxTiO3(BST)铁电薄膜的可行性。以醋酸钡[Ba(CH3COO)2]、碳酸锶[SrCO3]和钛酸四丁酯[Ti(OC4H9)4]作原料，运用一般的Sol-Gel工艺制备BST铁电薄膜，通过XRD分析物质结构，用SEM测定表面形貌，XPS及EDAX测定薄膜的组成。结果表明：采用碳酸锶原料和其他醇盐一起来制备BST铁电薄膜的方法是可行的。     

Polar Ceramics in RF-MEMS and Microwave Reconfigurable Electronics: A Brief Review on Recent Issues

Properties and fabrication status of microdevices for microwaves based on polar ceramics are reviewed. We discuss bulk acoustic wave devices with AlN films, rf-MEMS capacitive switches with high permittivity materials, and tunable ferroelectrics. The relevant properties of ferroelectrics for microwave applications are summarized with emphasis on composites and thin films.     

Preparation of BST thin films on Pt electrode on Si wafer with down-flow LSMCVD reactor

Abstract

A novel type of down-flow LSMCVD (Liquid Source Mist CVD) reactor was developed to prepare a high dielectric BST thin film on Pt electrode on Si wafer. Barium acetate [Ba (OOCCH₃)₂], strontium acetate [Sr (OOCCH₃)₂], and titanium isoproxide [Ti (OC₃H₇ ⁱ )₄] were used as metal sources. Metal sources were dissolved in acetic acid, 1-butanol, or 2-methoxyethanol. BST [Ba/(Ba + Sr) = 0.7] film annealed on Pt/Ti/SiO₂/Si above 650°C was polycrystalline. BST film has a (110) preferred orientation with increasing temperature. Surface roughness of BST film and grain size increased with increasing temperature. The metal-oxygen bond was formed at 650°C as shown in the spectra of FTIR. The depth profiles of elements of BST thin films indicated a uniform composition throughout the film. BST films annealed at 750°C showed a dielectric constant and a tanδ of 390 (thickness: 150 nm) and 0.06 at a frequency of 100 kHz, respectively. The behavior of capacitance of the BST film with bias voltage showed paraelectric property. BST film annealed at 750°C had the leakage current density of 3.2 (μA/cm²) at a bias voltage of 2V.     

High electric field-induced strain with ultra-low hysteresis and giant electrostrictive coefficient in barium strontium titanate lead-free ferroelectrics

Ferroelectrics with high electrostrictive properties are of great interest in fundamental researches and industrial applications. In this work, the phase structural evolution, dielectric properties as well as electrostrictive properties in barium strontium titanate [(Ba_1-xSr_x)TiO₃, BST] lead-free ferroelectrics with x from 0.05 to 0.4 were investigated in details. High electric field-induced strain (∼0.2%) at 60 kV/cm are obtained in x = 0.05 and 0.1 compositions. More importantly, almost purely positive strains with ultra-low hysteresis (<8%) determined from bipolar strain-electric field curves are observed in compositions with x from 0.05 to 0.3, suggesting the dominating role of electrostrictive effect. Temperature-insensitive and composition-insensitive longitudinal electrostrictive coefficient Q₃₃ for BST ceramics with giant values from 0.0409 m⁴/C² to 0.0479 m⁴/C² is identified. These features suggest that BST ceramics not only possess high electric field-induced strain with ultra-low hysteresis and giant Q₃₃, but also are good candidates for potential application in high-precision actuator devices.     

Microwave power detection using ferroelectric thin film varactors

ABSTRACT

LaAlO₃ powders are prepared by coprecipitation of La(OH)₃ and Al(OH)₃, followed by solid state reaction method or molten salt synthesis method. The crysatlline phase evolution, micro morphology and luminescence properties of the calcined products are systematically studied by XRD, SEM/EDX and fluorescence spectroscopy. The results show that LaAlO₃ powders with high purity could be obtained at 1000°C/3h with the help of melton salt Na₂SO₄, however, impurities exist in the solid state reaction products under the same calcination condition. The as prepared sub-micrometer LaAlO₃ powders doped with Eu³⁺ ion by the molten salt method show two dominant emmision peaks of 596nm and 618nm under excitation of near ultraviolet light (314nm), both emmision peak intensity reach maximum at the Eu³⁺ doping concentration of x = 0.08. At higher Eu³⁺ doping concentration, the emmision peak intensity decreases due to the concentration quenching.     

边界扫描测试中几类故障冲突解析

在介绍边界扫描测试应用系统的基础上,结合工程实例研究了边界扫描测试中出现的几类故障冲突,分析了产生的原因,对如何避免、解决此类故障冲突给出了解决方案,对从事该方面的应用测试研究有借鉴作用。     

稀土氧化物掺杂对BST陶瓷热释电性能的影响

采用轧膜成型工艺制备了掺杂有稀土氧化物的钛酸锶钡(BST)陶瓷,研究了不同稀土(Sc,Y,La,Ce,Pr,Nd和Sm)氧化物掺杂对其微观形貌、介电性能和热释电性能的影响。结果表明,Sc掺杂大幅降低了BST陶瓷的εr,严重劣化了BST陶瓷的热释电性能,并引起了长条状晶粒在BST陶瓷中的出现;Y掺杂则显著提高了BST陶瓷的热释电性能,并最终获得了εr为7111、tanδ为0.65×10–2、热释电系数p为5.5×10–7C·cm–2·℃–1、探测率优值Fd为8.49×10–5Pa–1/2的热释电BST陶瓷材料,有望在红外探测领域得到应用。     

The properties of Ba0.5Sr0.5TiO3 thin film prepared by RF magnetron sputtering from powder target

The Ba_0.5Sr_0.5TiO₃ (BST) thin film with the thickness of 400 nm deposited from powder target is prepared by the radio-frequency magnetron sputtering technique. The deposition rate of BST film is estimated to be 45 nm/min, which is very fast for ferroelectric materials. The dielectric properties of the as-prepared BST thin film are demonstrated. High dielectric tunability up to 42.7% and low dielectric loss small to 0.01 are achieved at a low applied voltage of 5 V. The results demonstrate that the RF magnetron sputtering from powder target is a versatile, novel technique for the deposition of high-quality ferroelectric thin films.