Multi-passband bandpass filters with low-temperature co-fired ceramic technology

The bandpass filters with multiple passbands have been proposed. To achieve multiple passbands, transmission lines shunted with short-circuit transmission lines are adopted. Moreover, the bandwidth of each passband can be controlled by properly choosing impedances and electrical lengths of the transmission lines and short-circuit transmission lines shunted. The design procedures of the proposed multi-passband filter are also described here. Finally, the agreement between the measured results and theoretical predictions sufficiently validates the proposed design and filter configuration.     

Design of four-ordered cross-coupled bandpass filters with low-temperature co-fired ceramic technology

A new method to realise the four-ordered quasi-elliptic bandpass filters with low-temperature co-fired ceramic technology has been proposed; in particular, the semi-lumped structure is employed. With the assistance of the non-adjacent cross coupling, a pair of transmission zeros can be generated on both sides of the passband skirt. Moreover, with the coupling between the source and load ports, an extra pair of transmission zeros will be generated so that there will be greater outband suppression on both sides of the passband skirt. The analysis and design procedures are provided. In addition, the match between the electromagnetic simulation and results of measurement validates the proposed structures.     

Synthesis of the low-temperature co-fired ceramic bandpass filters and diplexer with transmission zeros

The multilayered microwave filters are developed with the assistance of two transmission zeros. Besides a coupled line connected to one capacitor, another capacitor cross coupled between the source and load ports is utilised for the proposed filters. By properly adjusting the coupling coefficients between the coupled line and two capacitors, two transmission zeros would appear on the lower side, the higher side or on both sides of the passband skirt. Thus, the characteristics can be employed for diplexers or dual-band filters to make dual-mode portable telephones. Moreover, to miniaturise the circuit sizes and improve their performances, multilayered structure and the low-temperature co-fired ceramic technology are adopted for filter fabrication. The theorem of filter synthesis and procedures of filter design are also presented. Finally, the proposed structure is validated by an agreement between measured results of fabricated filters and the electromagnetic simulation.     

Design of low-temperature co-fired ceramic bandpass filter with transmission zeros in the stopband

A multilayered bandpass filter with low-temperature co-fired ceramic technology is proposed. By integrating two types of filters as one filter, four transmission zeros can be generated. Each type of filter with a source-load coupling capacitor and a grounded coupling inductor, simultaneously, can generate two transmission zeros located on the opposite side of the passband skirt separately. Moreover, the fabricated filter provides good matching with the electromagnetic simulation and can prove the availability of the filter configuration.     

Diffusivity of silver ions in the low temperature co-fired ceramic (LTCC) substrates

Diffusion of silver inner-electrode occurred during sintering of commercial low temperature co-fired glass ceramic substrate made the dielectric surface become light yellow. The samples added with silicon oxide (SiO₂) powder, however, maintained white color. Silicon-oxide powder was used to modified the sintering behavior and inhibit the silver ions diffusion for the LTCC ceramics. The alumina particles in the LTCC substrates could be regarded as the diffusion barrier of silver ions. The activation energy for silver ions diffusion in the LTCC substrates was 101 kJ/mol. When 5 wt% SiO₂ powder was added into the LTCC substrate, the diffusion activation energy of silver ions became 145 kJ/mol. At sintering temperature of 1180 K, the diffusion coefficient of silver ion in the LTCC ceramic substrates with and without additional SiO₂ were 8.88 × 10⁻¹³ cm²/s and 1.08 × 10⁻¹² cm²/s, respectively.     

Measurement of ion swarm distribution functions in miniature low-temperature co-fired ceramic ion mobility spectrometer drift tubes

Measurements of the performance of a miniature, portable 12-mm-diameter, 57-mm-length low-temperature cofired ceramic (LTCC) ion mobility spectrometer drift tube were undertaken to verify models of ion transport and determine the physical shape of the ion "swarms" in the LTCC tube. Simplified two-dimensional Gaussian models of ion swarm shape were fit to measured data to extract geometrical shape parameters. Results indicate that tube-transfer function effects that produce asymmetric ion swarms are minimized in the tube reducing temporal dispersion. Data are presented that illustrate the swarm shape as a function of gate time, electric field magnitude, and total charge in the ion swarm. Characterization and understanding of the ion transport mechanisms and effects that limit the resolution and other performance parameters of miniature IMS drift tubes is essential to the development of practical, robust, portable systems for "first responder" and homeland security missions.     

Porous ceramic lamellae for orthodontic ceramic brackets: Part I Fabrication and characterization

This study was undertaken to test a new and original orthodontic bracket base, consisting of a porous lamella, which was designed to facilitate removal of ceramic brackets from the enamel surface after treatment. In the phase of the study presented here, porous pellets were made by bonding coarse alumina particles (calcined or fused) with mullite, formed by their reaction with fine quartz particles during firing of the mixture at 1700°C. After machining the pellets to the desired shape, nine types of lamellae with different porosities were attached to the brackets using two different adhesive resins, and also bonded to bovine enamel using the same adhesives. The tensile bond strengths for the assemblies were determined so that the lamellae and the bonding adhesive that might be suitable for clinical application could be selected for testing in vitro in the second phase of the study.     

Preparation and properties of low-temperature co-fired ceramic of CaO–SiO2–B2O3 system

Low temperature co-fired ceramic (LTCC) was prepared by sintering a glass selected from CaO–SiO₂–B₂O₃ system, in which 0.5 wt% P₂O₅ and 0.5 wt% ZnO were added to optimize the preparation conditions. The glass powder and sintered bodies were characterized by different analytical techniques such as TG-DTA analysis, X-ray diffraction and Scanning electron microscopy. It was found that the optimal sintering temperature was 820°C based on the microstructure and the properties of sintering bodies, and then the major phases of the LTCC were CaSiO₃, CaB₂O₄ and SiO₂. The obtained products, with dielectric constant about 6.5, dielectric loss about 2 × 10⁻³ at 30 MHz and coefficient of thermal expansion about 8 × 10⁻⁶ °C⁻¹ between 20 and 400°C, are supposed to be suitable for application in wireless communications.     

Tough yttria-stabilized zirconia ceramic by low-temperature spark plasma sintering of long-term stored nanopowders

Weakly agglomerated 1.75 and 3 mol% yttria stabilized zirconia nanopowders were used in this study after six years of storage in vacuum-processed plastic containers. The proper storage conditions of the Y-TZP nanopowders avoided the hard agglomeration. Untreated and bead-milled nanopowders were used to obtain dense ceramics by slip casting and subsequent low-temperature sintering. Fully dense nanostructured 1.75Y-TZP and 3Y-YZP ceramics with and without doping of 1 wt% Al2O3 were produced by an optimized spark plasma sintering (SPS) technique at the temperatures of 1050-1150 degrees C at a pressure of 100 MPa. The SPS has revealed the clear advantage of consolidation of the weakly agglomerated nanopowders without preliminary deagglomeration. The Vickers hardness of both the low-temperature and spark plasma sintered samples was found to lie in the range of 10.98-13.71 GPa. A maximum fracture toughness of 15.7 MPa m(1/2) (average 14.23 MPa m(1/2)) was achieved by SPS of the 1.75Y-TZP ceramic doped with 1 wt% Al2O3 whereas the toughness of the 3Y-TZP ceramics with and without alumina doping was found to vary between 3.55 and 5.5 MPa m(1/2).     

Fabrication and characterization of dense zirconia and zirconia-silica ceramic nanofibers

The objective of this study was to prepare dense zirconia-yttria (ZY), zirconia-silica (ZS) and zirconia-yttria-silica (ZYS) nanofibers as reinforcing elements for dental composites. Zirconium (IV) propoxide, yttrium nitrate hexahydrate, and tetraethyl orthosilicate (TEOS) were used as precursors for the preparation of zirconia, yttria, and silica sols. A small amount (1-1.5 wt%) of polyethylene oxide (PEO) was used as a carry polymer. The sols were preheated at 70 degrees C before electrospinning and their viscosity was measured with a viscometer at different heating time. The gel point was determined by viscosity-time (eta-t) curve. The ZY, ZS and ZYS gel nanofibers were prepared using a special reactive electrospinning device under the conditions near the gel point. The as-prepared gel nanofibers had diameters between 200 and 400 nm. Dense (nonporous) ceramic nanofibers of zirconia-yttria (96/4), zirconia-silica (80/20) and zirconia-yttria-silica (76.8/3.2/20) with diameter of 100-300 nm were obtained by subsequent calcinations at different temperatures. The gel and ceramic nanofibers obtained were characterized by scanning electron microscope (SEM), high-resolution field-emission scanning electron microscope (FE-SEM), thermogravimetric analyzer (TGA), differential scanning calorimeter (DSC), Fourier transform infrared spectrometer (FT-IR), and X-ray diffraction (XRD). SEM micrograph revealed that ceramic ZY nanofibers had grained structure, while ceramic ZS and ZYS nanofibers had smooth surfaces, both showing no visible porosity under FE-SEM. Complete removal of the polymer PEO was confirmed by TGA/DSC and FT-IR. The formation of tetragonal phase of zirconia and amorphous silica was proved by XRD. In conclusion, dense zirconia-based ceramic nanofibers can be fabricated using the new reactive sol-gel electrospinning technology with minimum organic polymer additives.     

低温烧结铁氧体/陶瓷复合材料的电磁性能研究

采用MgCuZn铁氧体(MCZF)分别与少量CaTiO3(CT)和BaTiO3(BT)复合,以Bi2O3为助熔剂,通过标准陶瓷工艺在900和950℃烧结得到适合低温共烧陶瓷(LTCC)工艺的两类复合材料MCZF/CT和MCZF/BT。对比研究铁氧体与两类复合材料的磁性能和介电性能发现,与陶瓷复合后材料的截止频率可以从13.9MHz提高到136.5MHz,而1MHz处的介电损耗可以从0.741降低到0.012。对比研究不同烧结温度下复合材料的电磁性能发现,950℃烧结的样品比900℃烧结时有更高的起始磁导率、Snoek产量、介电常数及更低的介电损耗,其中MCZF/CT的起始磁导率达到51.8,明显高于MCZF/BT,但后者有更优良的介电频率特性。此外,结合微结构分析讨论了950℃烧结样品的电磁性能变化原因。     

HA-n-ZrO2核壳层复合陶瓷微粉材料的制备与表征

采用水热-沉积原位分步反应法.制备了羟基磷灰石(HA)-氧化锆(ZrO2)复合微粉,采用XRD和TEM对复合微粉的物相、形貌和大小进行了表征.对复合微粉进行模压成型、热处理制备了复合陶瓷试样,并测试其力学性能.结果表明:所得复合微粉以纳米级四方相ZrO2为"核心",逐层包覆HA,形成核-壳层结构(HA-n-ZrO2);...     

Continuous flow analytical microsystems based on low-temperature co-fired ceramic technology. Integrated potentiometric detection based on solvent polymeric ion-selective electrodes

In this paper, the low-temperature co-fired ceramics (LTCC) technology, which has been commonly used for electronic applications, is presented as a useful alternative to construct continuous flow analytical microsystems. This technology enables not only the fabrication of complex three-dimensional structures rapidly and at a realistic cost but also the integration of the elements needed to carry out a whole analytical process, such as pretreatment steps, mixers, and detection systems. In this work, a simple and general procedure for the integration of ion-selective electrodes based on liquid ion exchanger is proposed and illustrated by using ammonium- and nitrate-selective membranes. Additionally, a screen-printed reference electrode was easily incorporated into the microfluidic LTCC structure allowing a complete on-chip integration of the potentiometric detection. Analytical features of the proposed systems are presented.     

A simple and an effective method for the fabrication of densified glass-ceramics of low temperature co-fired ceramics

This study reports a new, simple and effective pre-calcined method for fabrication BaO–TiO₂–B₂O₃–SiO₂ low temperature co-fired ceramics (LTCC) at a sintering temperature below 900 °C, and with dielectric losses (tan δ) lower than 2 × 10⁻³. The research results have shown that the addition of 2–5 wt% Al₂O₃ could easily eliminate the porosity of the glass-ceramics because of the excellent wetting behavior between alumina and the BaO–B₂O₃–SiO₂ glass liquid phase in the low temperature co-fired ceramic system.     

Synthesis and characterization of Ba2−xSrxEuSbO6 ceramic substrates for YBCO films

A group of complex perovskites, Ba2−xSrxEuSbO6 (where x=0, 1 and 2) was synthesized and sintered as single-phase materials for their use as substrates for YBCO superconductor films. These compounds have a complex cubic perovskite (A2BB′O6) crystal structure with lattice constant in the range 0.85–0.83 nm. The values of dielectric constant and loss factor of Ba2−xSrxEuSbO6 compounds are in the range suitable for their use as substrates for microwave applications of superconductor films. The dielectric constant decreases with increase of strontium content. No chemical reaction was observed between YBCO and Ba2−xSrxEuSbO6 ceramics even when they were mixed in composites of the form 80 vol% YBCO–20 vol% Ba2−xSrxEuSbO6 and processed under severe heat treatment. Addition of up to 20 vol% Ba2−xSrxEuSbO6 to YBCO showed no detrimental effect on superconducting properties of YBCO. The YBCO thick films developed on sintered specimens by dip coating were textured and showed (0 0 l) orientation with Tc(0)=92 K. This revised version was published online in November 2006 with corrections to the Cover Date.     

陶瓷／金属梯度热障涂层的制备及性能评价

为了评价陶瓷／金属梯度热障涂层的性能，设计了4种涂层方案和2种基体材料（1Cr18Ni9Ti和2Cr13）．利用单枪单送粉器成功地制备了线性梯度涂层．通过观察涂层的微观结构、测量涂层的抗热震性能和热残余应力来评价涂层的性能．利用扫描电镜对各种陶瓷涂层的微观结构进行了观察和分析，利用X射线能谱分析得到了陶瓷梯度涂层试样中的不同区域的衍射图．热震试验表明，梯度涂层比非梯度涂层具有更好的抗热震性能．采用钻孔法对不同涂层方案进行了残余应力的测量，结果表明，压应力出现在1Cr18Ni9Ti基体材料上，而拉应力出现在2Cr13基体材料上．     

Fabrication and characterization of nanostructures on insulator substrates by electron-beam-induced deposition

Abstract

The fabrication, characterization, and decoration with metallic nanoparticles of nanostructures such as nanowhiskers, nanodendrites, and fractal-like nanotrees on insulator substrates by electron-beam-induced deposition (EBID) are reviewed. Nanostructures with different morphologies of whiskers, dendrites, or trees are fabricated on insulator (Al₂O₃ or SiO₂) substrates by EBID in transmission electron microscopes by controlling the irradiation conditions such as the electron beam intensity. The growth of the nanostructure is related to the accumulation of charges on the surface of a substrate during electron-beam irradiation. A high concentration of the target metallic element and nanocrystal grains of the element are contained in the fabricated nanostructures. The process of growth of the nanostructures is explained qualitatively on the basis of mechanisms in which the formation of the nanostructures is considered to be related to the nanoscaled unevenness of the charge distribution on the surface of the substrate, the movement of the charges to the convex surface of the substrate, and the accumulation of charges at the tip of the grown nanostructure. Novel composite structures of Pt nanoparticle/tungsten (W) nanodendrite or Au nanoparticle/W nanodendrite are fabricated by the decoration of W nanodendrites with metallic elements. Because they have superior features, such as a large specific surface area, a freestanding structure on substrates, a typical size of several nanometers of the tip or the branch, and high purity, the nanostructures may have applications in technologies such as catalysts, sensors, and electron emitters. However, there are still some subjects that should be further studied before their application.     

Fabrication and characterization of ferroelectric PLZT film capacitors on metallic substrates

We have grown ferroelectric Pb_0.92La_0.08Zr_0.52Ti_0.48O₃ (PLZT) films on Hastelloy C276 (HC) substrates by chemical solution deposition. Samples of 1.15-μm-thick PLZT films were prepared on HC with and without lanthanum nickel oxide (LNO) films as an intermediate buffer layer. On samples with and without LNO buffers at room temperature, we measured dielectric constants of ≈1,300 and ≈450 and loss tangents of ≈0.06 and ≈0.07, respectively. For PLZT films grown on HC with LNO buffer, the dielectric constant increases, while the dielectric loss decreases, with increasing temperature. A dielectric constant of ≈2,000 and loss of ≈0.05 were observed at 150 °C. Samples with LNO buffer also exhibited slimmer hysteresis loops and lower leakage current density when compared to samples without LNO buffer. The following results were measured on samples with and without LNO buffers: remanent polarization (P _r) values of 21.3 and 36.4 μC/cm², coercive electric field (E _c) values of 41 and 173 kV/cm, and leakage current densities of ≈1.1 × 10⁻⁸ and ≈1.6 × 10⁻⁷ A/cm², respectively. The energy storage capability was measured at ≈65 J/cm³ for the PLZT film-on-foil capacitor deposited on HC with LNO buffer.     

Fabrication and characterization of perovskite ferroelectric PMN/PT ceramic nanocomposites

The potential of a ceramic nanocomposite technique employing a simple bimodal particle size packing and a pressureless sintering process as a low-cost and simple ceramic processing to obtain perovskite ferroelectric ceramics in the PMN/PT system was demonstrated. Attention was focused on relationships between chemical composition, densification, microstructure, and electrical properties. It has been found that the phase formation, microstructures, and dielectric properties of ceramic nanocomposites are totally different from those of typical solid solutions.     

Fabrication and characterization of nanostructures on insulator substrates by electron-beam-induced deposition

The fabrication, characterization, and decoration with metallic nanoparticles of nanostructures such as nanowhiskers, nanodendrites, and fractal-like nanotrees on insulator substrates by electron-beam-induced deposition (EBID) are reviewed. Nanostructures with different morphologies of whiskers, dendrites, or trees are fabricated on insulator (Al₂O₃ or SiO₂) substrates by EBID in transmission electron microscopes by controlling the irradiation conditions such as the electron beam intensity. The growth of the nanostructure is related to the accumulation of charges on the surface of a substrate during electron-beam irradiation. A high concentration of the target metallic element and nanocrystal grains of the element are contained in the fabricated nanostructures. The process of growth of the nanostructures is explained qualitatively on the basis of mechanisms in which the formation of the nanostructures is considered to be related to the nanoscaled unevenness of the charge distribution on the surface of the substrate, the movement of the charges to the convex surface of the substrate, and the accumulation of charges at the tip of the grown nanostructure. Novel composite structures of Pt nanoparticle/tungsten (W) nanodendrite or Au nanoparticle/W nanodendrite are fabricated by the decoration of W nanodendrites with metallic elements. Because they have superior features, such as a large specific surface area, a freestanding structure on substrates, a typical size of several nanometers of the tip or the branch, and high purity, the nanostructures may have applications in technologies such as catalysts, sensors, and electron emitters. However, there are still some subjects that should be further studied before their application.