Preparation and characterization of TaAlOx high-κ dielectric for metal-insulator-metal capacitor applications

Metal-insulator-metal (MIM) capacitors with excellent electrical properties have been fabricated using high-κ TaAlO_x-based dielectrics. TaAlO_x films having thickness of 11.5-26.0 nm, with equivalent oxide thickness (EOT) of ~ 2.3-5.3 nm were deposited on top of Au/SiO₂ (180 nm)/Si (100) structures by radio frequency magnetron co-sputtering of Ta₂O₅ and Al₂O₃ targets. The surface chemical states of the as-deposited TaAlO_x films were characterized by high-resolution X-ray photoelectron spectroscopy. The crystallinity of the TaAlO_x films for various post-deposition annealing treatments was characterized by grazing incident X-ray diffraction, which reveals that an amorphous phase is still retained for rapid thermal annealing up to 500 °C. Besides a high capacitance density (~ 5.4 to 6.6 fF/μm² at 1 kHz), a low value of voltage coefficients of capacitance and a stable temperature coefficient of capacitance have also been obtained in MIM capacitors with TaAlO_x films. Degradation phenomenon of TaAlO_x-based MIM capacitors under constant current stressing at 20 nA is found to be strongly dependent on dielectric thickness. It is shown that Al-incorporated Ta₂O₅ (TaAlO_x) films with high band gap and good thermal stability, low leakage current and good voltage linearity make it one of the most promising candidates for metal-insulator-metal capacitor applications.     

Synthesis and characterization of Fe–B nanoparticles for potential magnetic applications

The crystallization and structure of Fe–B nanoparticles (NPs) of different sizes formed in a single process by gas aggregation from Fe₈₀B₂₀ targets were analyzed by transmission electron microscopy. It is concluded that all NPs are covered by an amorphous Fe–B shell while the crystal structure of the NPs core depends on their size. Large NPs with diameters ≥30 nm are monocrystalline tetragonal Fe₃B, small diameter NPs (≤20 nm) are completely amorphous whereas in middle size NPs, with diameters between 20 and 30 nm, difference Fe–B phases (tetragonal Fe₃B and orthorhombic FeB) together with defaulted areas are observed. This work opens new possibilities to produce Fe–B NPs tailoring their magnetic properties by controlling their size and composition.     

Preparation and characterization of as-extruded Mg–Sn alloys for orthopedic applications

In this study, as-extruded Mg–Sn alloys with various Sn content were prepared and characterized for orthopedic applications. The results of microstructure observations and X-ray diffraction analysis showed that as-extruded Mg–Sn alloys were composed of α-Mg and Mg₂Sn phases, and the content of Mg₂Sn phase increased with increasing Sn content. The microstructure of as-extruded Mg–Sn alloy with 1 wt.% Sn was equiaxed grain, while the one with a higher Sn content was inhomogeneous microstructure and the grain size of the long elongated grains decreased with increasing Sn content. Tensile test revealed that the yield strength and ultimate tensile strength of as-extruded Mg–Sn alloys increased while the elongation decreased with increasing Sn content. Immersion and electrochemical tests indicated that the microstructure of as-extruded Mg–Sn alloys affected their corrosion properties, and the increase of Mg₂Sn phase resulted from the increase of the Sn content led to a higher corrosion rate. The cytotoxicity test showed that as-extruded Mg–1Sn and Mg–3Sn alloys met the requirement of cell toxicity for orthopedic applications. Our analyses showed that as-extruded Mg–1Sn and Mg–3Sn alloys were promising to be used as biodegradable orthopedic implants.     

Synthesis and characterization of hollow glass–ceramics microspheres

Hollow glass–ceramics microspheres (HGCMs), with the diameter from 10 to 60 μm and the shell thickness less than 2 μm, were successfully fabricated by a simple technique using polyacrylamide microspheres (PAMs) as template. The corresponding HGCM were obtained after a thermal treatment of the core–shell microspheres, which were synthesized with organic template method. The size, morphology and phase composition of synthesized products were determined via XRD, SEM, TGA. The effects of the amount of glass powder, the Hydrophile–Lipophile Balance (HLB) value, the sintering temperature, and the ratio of pre-adsorbed water to the water in the slurry on the morphologies of HGCM have been investigated. The results showed that the agglomeration of HGCM can be reduced by adjusting the HLB value. In addition, the amount of solid beads decreases obviously by reducing ratios and adjusting the HLB value. As the sintering temperature increases, the surface of the HGCM becomes smooth and compact. Meanwhile, computational investigations are carried out to better understand the strengthen effect of taking glass–ceramics materials in the system MgO–Al₂O₃–SiO₂ (MAS) as shell materials.     

Three-phase polymer–ceramic–metal composite for embedded capacitor applications

This paper addresses the materials and processes for printed wiring board compatible embedded capacitor using ceramic, polymer and metal. The Ca[(Li_1/3Nb_2/3)_0.8Ti_0.2]O_3?δ (CLNT)–epoxy–silver, three-phase composites were prepared by two step mixing and thermosetting technique. The dielectric properties of the three-phase composites were investigated in terms of volume fraction of silver, temperature and frequency. The dielectric properties of epoxy–CLNT composites were compared with theoretical predictions. The relative permittivity of the three-phase composites increased with silver loading. Addition of 0.28 volume fraction of silver increases the relative permittivity of epoxy–CLNT composites from 8 to 142 at 1 MHz. This composite is flexible and can be fabricated into various shapes with low processing temperature.     

Dielectric tunable properties of Ba0.5Sr0.5TiO3–MgMoO4 composite ceramics for microwave applications

(1?x) Ba_0.5Sr_0.5TiO₃–xMgMoO₄ (x = 0, 5, 10, 20 and 30 wt%) composite ceramics were prepared via solid state reaction processing. Their structure and dielectric properties were systematically characterized. The introduction of MgMoO₄ resulted in a change in lattice constant of the perovskite phase and partial reaction between MgMoO₄ and Ba_0.5Sr_0.5TiO₃ occurred in the sintering process. Both X-Ray Diffraction (XRD) and Back-scattered Electron Images (BEI) analysis show the co-existence of three phase structures of BST, MgMoO₄ and BaMoO₄. With increasing of MgMoO₄ content, the tunability of the composite ceramics was decreased due to the increase of the amount of non-ferroelectric phases. The Curie temperature Tc of the samples gradually shifted to low temperatures with increasing of MgMoO₄ content. Dielectric constant can be adjusted in the range from 2035 to 150, meanwhile maintain a relatively high tunability and Q values. The sample with 20 wt% MgMoO₄ possesses a tunability of 10 %, a low dielectric constant of 111 and an appropriate Q value of 183 (2.240 GHz), which meet the requirements of high power and impedance matching, thus making it a promising candidate for applications as electrically tunable microwave devices.     

Synthesis and characterization of low cost willemite based glass–ceramic for opto-electronic applications

This paper presents a comprehensive study on thermal, structural and optical properties of novel willemite glass–ceramics. The precursor glass in the ZnO–SLS glass system was successfully prepared using conventional melt-quenching technique and willemite (Zn₂SiO₄) glass–ceramics were derived from this precursor glass by a control crystallization process. The effect of heat-treatment temperature on the phase transformation, morphology and size of Zn₂SiO₄ crystal phase was examined using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) techniques. Furthermore, fourier transform infrared reflection (FTIR) spectroscopy was used to evaluate the Zn₂SiO₄ crystal structural evolution. The average size of Zn₂SiO₄ crystallite obtained from calculation of XRD is found to be in the range 30–60 nm, whereas the grain size observed in FESEM is in range of 200–400 nm. The appearance of SiO₂, ZnO₄ and Zn–O–Si bands detected from FTIR indicate the formation of Zn₂SiO₄ crystal phase. Besides, the study of the optical band gap has found that optical band gap of the glass–ceramics decreased as the heat treatment temperature increased. The photoluminescence spectra of willemite glass–ceramics exhibit two different emissions around 525 nm (green) and 585 nm (yellow); exhibit a characteristic of broad absorption band around 260 nm. These two different spectra reveal that the luminescence performance of the willemite glass–ceramics was enhanced with the progression of heat treatment temperature due to different located energy levels of the β-Zn₂SiO₄ and α-Zn₂SiO₄ crystalline phase. Such luminescent glass–ceramics was expected to find potential applications in phosphors and opto-electronic devices.     

Fabrication and characterization of porous Ti–7.5Mo alloy scaffolds for biomedical applications

Porous titanium and titanium alloys are promising scaffolds for bone tissue engineering, since they have the potential to provide new bone tissue ingrowth abilities and low elastic modulus to match that of natural bone. In the present study, porous Ti–7.5Mo alloy scaffolds with various porosities from 30 to 75 % were successfully prepared through a space-holder sintering method. The yield strength and elastic modulus of a Ti–7.5Mo scaffold with a porosity of 50 % are 127 MPa and 4.2 GPa, respectively, being relatively comparable to the reported mechanical properties of natural bone. In addition, the porous Ti–7.5Mo alloy exhibited improved apatite-forming abilities after pretreatment (with NaOH or NaOH + water) and subsequent immersion in simulated body fluid (SBF) at 37 °C. After soaking in an SBF solution for 21 days, a dense apatite layer covered the inner and outer surfaces of the pretreated porous Ti–7.5Mo substrates, thereby providing favorable bioactive conditions for bone bonding and growth. The preliminary cell culturing result revealed that the porous Ti–7.5Mo alloy supported cell attachment.     

Preparation and comparative characterization of keratin–chitosan and keratin–gelatin composite scaffolds for tissue engineering applications

We report fabrication of three dimensional scaffolds with well interconnected matrix of high porosity using keratin, chitosan and gelatin for tissue engineering and other biomedical applications. Scaffolds were fabricated using porous Keratin–Gelatin (KG), Keratin–Chitosan (KC) composites. The morphology of both KG and KC was investigated using SEM. The scaffolds showed high porosity with interconnected pores in the range of 20–100 μm. They were further tested by FTIR, DSC, CD, tensile strength measurement, water uptake and swelling behavior. In vitro cell adhesion and cell proliferation tests were carried out to study the biocompatibility behavior and their application as an artificial skin substitute. Both KG and KC composite scaffolds showed similar properties and patterns for cell proliferation. Due to rapid degradation of gelatin in KG, we found that it has limited application as compared to KC scaffold. We conclude that KC scaffold owing to its slow degradation and antibacterial properties would be a better substrate for tissue engineering and other biomedical application.     

Synthesis and characterization of a new liquid polymer precursor for Si–B–C–N ceramics

A new liquid polyborosilazane precursor for Si–B–C–N ceramic was synthesized by co-condensation reaction of boron trichloride, organodichlorosilanes, and hexamethyldisilazane. The structure and properties of polyborosilazane were studied by means of Fourier transform-infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), rheology, and thermogravimetric analysis (TGA). The conversion of polymer to ceramic and the high-temperature behavior of the new polymer-derived ceramic were investigated by TG–MS, FT-IR, X-ray diffraction (XRD) and high-temperature TGA (HTGA). The ceramics showed good oxidative resistance and thermal stability with weight gain of 1.8 wt% at 1350 °C under air atmosphere and weight loss of 2.6% at 1900 °C under Ar atmosphere.     

Low temperature synthesis and characterization of strontium stannate–titanate ceramics

A novel modified chimie douce synthetic approach based on the gel to crystallite conversion (G–C) method has been developed to prepare strontium titanate SrTiO₃, strontium stannate SrSnO₃, and mixed strontium stannate–titanate SrSn_1−xTi_xO₃ (x = 0.05–0.5). The obtained materials were characterized by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). The formation of fully crystalline SrTiO₃ was observed in the temperature range of 800–1000 °C. The formation of monophasic SrSnO₃ occurs in the temperature range of 700–900 °C. At lower and higher temperatures the formation an impurity phases such as SrCO₃ and SnO₂ takes place. The same synthetic approach has been applied for the preparation of mixed strontium stannates–titanates SrSn_1−xTi_xO₃. The SEM images of SrTiO₃ samples indicated that the powder particles are 1–5 μm in size having approximately plate-like shape. Quite different surface morphology was determined for SrSnO₃ samples revealing the size of crystals from 500 nm to 40 μm. For the composition with x = 0.15, it was observed that the grain growth is uniform and the size of the grains is of the order of ∼2–5 μm.     

Synthesis and characterization of silica–lead sulfide core–shell nanospheres for applications in optoelectronic devices

Nanoscale miniaturization of chalcogenide semiconductors such as lead sulfide (galena) can generate interesting quantum confinement effects in the field of optoelectronic applications. In this work, we developed a process in order to obtain SiO₂ nanospheres coated with Galena, as the denominated core–shell system; this process is based on Stöber’s method, where the magnetic stirring was replaced by an ultrasonic bath to achieve well rounded and highly stable silica nanoparticles with diameters average of 70 nm. The PbS shell cover presents a thickness of 10 nm around. The nanostructures’ chemical composition, morphology, and optical properties were determined by transmission electron microscopy and UV–Vis spectroscopy. As a result, the nanoshells correspond to cubic PbS, presenting some interplanar distances of 2.95 Å and 3.41 Å; this nanoshell also shown an optical spectrum shift toward blue and a remarkable increase of 3.75 eV in its band gap, compared with the PbS bulk value. The chemical composition is studied by energy scattering spectroscopy and X-ray photoelectron spectroscopy analysis.

     

Preparation and characterization of PAN–KI complexed gel polymer electrolytes for solid-state battery applications

The free standing and dimensionally stable gel polymer electrolyte films of polyacrylonitrile (PAN): potassium iodide (KI) of different compositions, using ethylene carbonate as a plasticizer and dimethyl formamide as solvent, are prepared by adopting ‘solution casting technique’ and these films are examined for their conductivities. The structural, miscibility and the chemical rapport between PAN and KI are investigated using X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry methods. The conductivity is enhanced with the increase in KI concentration and temperature. The maximum conductivity at 30°C is found to be 2.089 × 10^?5 S cm^?1 for PAN:KI (70:30) wt%, which is nine orders greater than that of pure PAN (< 10^?14 S cm^?1). The conductivity-temperature dependence of these polymer electrolyte films obeys Arrhenius behaviour with activation energy ranging from 0.358 to 0.478 eV. The conducting carriers of charge transport in these polymer electrolyte films are identified by Wagner’s polarization technique and it is found that the charge transport is predominantly due to ions. The better conducting sample is used to fabricate the battery with configuration K/PAN + KI/I₂+ C + electrolyte and good discharge characteristics of battery are observed.     

The effect of ZrO2 and TiO2 on solubility and strength of apatite–mullite glass–ceramics for dental applications

The effect of ZrO₂ and TiO₂ on the chemical and mechanical properties of apatite–mullite glass–ceramics was investigated after sample preparation according to the ISO (2768:2008) recommendations for dental ceramics. All materials were characterized using differential thermal analysis, X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. X-ray fluorescence spectroscopy was used to determine the concentrations of elements present in all materials produced. The chemical solubility test and the biaxial flexural strength (BFS) test were then carried out on all the samples. The best solubility value of 242 ± 61 μg/cm² was obtained when HG1T was heat-treated for 1 h at the glass transition temperature plus 20 °C (T_g + 20 °C) followed by 5 h at 1200 °C. The highest BFS value of 174 ± 38 MPa was achieved when HG1Z and HG1Z+T were heat-treated for 1 h at the T_g + 20 °C followed by 7 h at 1200 °C. The present study has demonstrated that the addition of TiO₂ to the reference composition showed promise in both the glass and heat-treated samples. However, ZrO₂ is an effective agent for developing the solubility or the mechanical properties of an apatite–mullite glass–ceramic separately but does not improve the solubility and the BFS simultaneously.     

Synthesis, characterization, and sintering of sol–gel derived cordierite ceramics for high-frequency MLCIs

The synthesis, characterization, and sintering of sol–gel derived cordierite ceramics are investigated in the present paper. Synthesis was carried out by optimizing two main preparation parameters. The effect of the heat-treatment schedule on crystallization and the properties of crystalline phases were analyzed. The additives B₂O₃ and P₂O₅ were utilized to promote the crystallization or transformation to -cordierite and sintering. This material has a low dielectric constant and a low dissipation factor and can be co-fired with high conductivity metals such as Au, Ag/Pd, Cu paste at low temperature (below 1000 °C), suggesting that it would be a promising material for high-frequency MLCIs.     

Nanostructures bilayer ZnO/MgO dielectrics for metal–insulator–metal capacitor applications

Bilayer ZnO/MgO dielectrics for metal–insulator–metal (MIM) capacitor application were successfully deposited using simple chemical technique which is sol–gel spin coating method with different annealing temperatures. Important criteria in determining good dielectric layer have been investigated which include structural, electrical and dielectric properties. Cubic-like grain was observed for films annealed at 400 and 425 °C which enhance the carrier density and polarization that resulted in high k value produced. Bilayer film annealed at 475 °C improved in small surface roughness (17.629 nm), minimum leakage current density (~10^?8 A cm^?2) and high resistivity (3.14 × 10⁵ Ω cm). Dielectric constant, k was varied with frequency and k value was found to be 5.09 at 10 kHz. The results obtained in this study indicated that film annealed at temperature of 475 °C is suitable to be used as dielectrics for MIM capacitor application.     

Design and characterization of new Cu alloys to substitute Cu–25%Ni for coinage applications

As the material and manufacturing cost of coins approached or even exceeded the face value of coins over the last 10 years, the needs to develop less-expensive alloys to replace the current coinage materials increased. The objective of this study is to develop new cost-effective alloys with the same vending machine acceptability and similar color tone as Cu–25%Ni coins. Cu–Zn–Ni–Fe and Cu–Zn–Ni–Fe–Cr alloys developed in this study were found to have the electrical conductivity close to and color similar to that of Cu–25Ni. The strengths of the annealed Cu–25.5%Zn–12%Ni–1.5%Fe and Cu–25.5%Zn–12%Ni–1.5%Fe–0.28%Cr alloys were observed to be 451 MPa and 512 MPa, respectively, with excellent ductility, suggesting that these alloys could be substitutive to Cu–25%Ni alloy for other general structural applications as well as coinage application. Both alloys exhibited the typical ductile fracture surfaces. Cu–Zn–Ni–Fe alloy was found to be a better candidate for coins because of the better formability and machinability associated with its moderate strength and excellent ductility.     

Investigation and characterization of densification,processing and mechanical properties of TiB2–SiC ceramics

In the present work, high-frequency induction heating was firstly used to densify TiB₂–SiC ceramic, and the microstructure analysis indicated that the average grain size of the sample, which was sintered through induction heating, was smaller than that of the sample sintered through hot-pressing. The flexural strength and fracture toughness were improved after refining the grains and increasing the relative density. In order to characterize the densification behavior of TiB₂–SiC ceramic sintered through induction heating, the typical curve of measured linear shrinkage of a sample was calculated and used. The tangential and normal grinding forces were substituted by the horizontal and vertical forces measured from the dynamometer in order to characterize intuitively the effect of grinding parameters on the microstructure and residual stress. The above-mentioned results revealed that the high-frequency induction heating has more advantages over hot-pressing. The results and way of these works can be applied to aid materials engineering design for the development of new materials, quality assurance, and characterization assessment of durability.