Journal of Electronic Materials

The powder-in-tube process has been used to fabricate long lengths of flexible, high-Jc, silver-clad Bi-2223 HTS conductors. By improving thermomechanical processing and precursor powder preparation, we have succeeded in achieving Jc values of≥4×104 A/cm2 at liquid nitrogen (77K) temperature and >105 A/cm2 at liquid helium (4.2K) and liquid neon (27K) temperatures in short tape samples. Detailed measurements with high applied magnetic fields are reported. Several long tapes up to 10 m in length have also been fabricated and cowound into small superconducting pancake coils by the “wind-and react” approach. Transport measurements at 77 and 4.2K for these coils are also reported.

Copper micropillars plated onto a silicon die and soldered with Sn-Ag solder to a copper lead frame in a flip chip on lead package have been subjected to high-temperature storage at 150°C and 175°C for 500 h, 1000 h, and 1500 h. Cu6Sn5 and Cu3Sn intermetallic compounds were found on both sides of the solder, but the growth rates were not the same as evidenced by different values of the growth exponent n. Cu and Sn diffusion controlled the Cu3Sn growth in the Cu pillar interface (n ≈ 0.5), while interface reactions controlled the growth in the Cu lead frame interface (n ≈ 0.8). Increasing the aging temperature increased the growth of Cu3Sn as well as the presence of microvoids in the Cu lead frame side. Adding Ni as a barrier layer on the Cu pillar prevented the growth of Cu3Sn in the Cu pillar interface and reduced its growth rate on the lead frame side, even at higher aging temperatures.

A series of epitaxial 4H-SiC thin films grown by low pressure chemical vapor deposition (LPCVD) were characterized using various techniques, including x-ray diffraction (XRD), Fourier transform infrared (FTIR) reflectance, Raman scattering, and x-ray photoelectron spectroscopy (XPS). The epilayers were grown on heavily doped n-type 4H-SiC substrates using different gas compositions. XRD showed that the thin films were single crystal. Raman scattering identified the films to be 4H polytype. FTIR reflectivity spectra indicated improvement in the film quality over that of the substrate and atmospheric pressure-grown epilayers. XPS scans revealed the existence of Si, C, and O along with C-contaminant species in the form of CH and carbon oxides. Variations in crystalline quality, optical, and surface properties with the growth conditions were studied. This study also provides an important comparison between low and atmospheric pressure-grown 4H-SiC epilayers.

In situ observation was performed on cross-sections of Sn-3.0Ag-0.5Cu solder interconnects to track the evolution of microstructure and grain orientation under electrical current stressing. Cross-sections of Cu/Ni–Sn-3.0Ag-0.5Cu–Ni/Cu sandwich-structured solder interconnects were prepared by the standard metallographic method and subjected to electrical current stressing for different times. The electron backscatter diffraction technique was adopted to characterize the grain orientation and structure of the solder interconnects. The results show that metallization dissolution and intermetallic compound (IMC) migration have close relationships with the grain orientation and structure of the solder interconnects. Ni metallization dissolution at the cathode interface and IMC migration in the solder bulk can be accelerated when the c-axis of the grain is parallel to the electron flow direction, while no observable change was found when the c-axis of the grain was perpendicular to the electron flow direction. IMC can migrate along or be blocked at the grain boundary, depending on the misorientation between the current flow direction and grain boundary.

Calcium titanate (CaTiO3)-filled butyl rubber (BR) composites were fabricated by mixing and hot pressing. The filler volume fraction was varied from 0 to 50%, and its effects on properties such as density, moisture absorption, dielectrics, coefficient of thermal expansion (CTE), thermal conductivity and thermal stability were studied. The phase purity of the powder was confirmed by x-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS), while scanning electron microscopy (SEM) was used to analyze the dispersion, morphology and microstructure of the samples. Optimal dielectric and thermal properties were obtained for the sample having 45% filler volume fraction. Relative permittivity (εr) of 11.7, along with a low loss tangent (tan δ) of 0.0053, was achieved at the optimal filler content in the X-band (8.2–12.4 GHz) regime. A low CTE of 33.7 ppm/°C and low moisture absorption of 0.0798%, along with good thermal stability and acceptable thermal conductivity (0.6303 W/m K), were also obtained for the optimum filled sample. Moreover, an elongation of 31.9% was observed without any permanent deformation. The developed highly flexible dielectric substrate material can be effectively used for miniaturized flexible microwave circuit applications.

We have investigated the thermoelectric properties of p-type Na-doped Mg2 Si0.25Sn0.75 solid solutions prepared by liquid–solid reaction and hot-pressing methods. Na was introduced into Mg2Si0.25Sn0.75 by using either sodium acetate (CH3COONa) or metallic sodium (2 N). The samples doped with sodium acetate consisted of phases with antifluorite structure and a small amount of MgO as revealed by x-ray diffraction, whereas the sample doped with metallic sodium contained the Sn, MgO, and Mg2SiSn phases. The hole concentrations of Mg1.975Na0.025Si0.25Sn0.75 doped by sodium acetate and metallic sodium were 1.84 × 1025 m−3 and 1.22 × 1025 m−3, respectively, resulting in resistivities of 4.96 × 10−5 Ω m (sodium acetate) and 1.09 × 10−5 Ω m (metallic sodium). The Seebeck coefficients were 198 μV K−1 (sodium acetate) and 241 μV K−1 (metallic sodium). The figures of merit for Mg1.975Na0.025Si0.25Sn0.75 were 0.40 × 10−3 K−1 (sodium acetate) and 0.25 × 10−3 K−1 (metallic sodium) at 400 K. Thus, sodium acetate is a suitable Na dopant for Mg2Si1−x Sn x .

Schiff base ligand, (E)-methyl 2-(5-bromo-2-hydroxybenzylideneamino)-6-phenyl-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate (L) generated from condensation of 5-bromo-salicylaldehyde with methyl 2-amino-6-methyl-4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3-carboxylate and its Co(II) and Pd(II) metal complexes were prepared by using a molar ratio of ligand:metal as 1:1. The complex compounds were obtained by the coordination of donor atoms of the ligand according to the spectral data. The structures of the obtained complex compounds were determined by elemental analysis, fourier transform infrared, 1H and 13C nuclear magnetic resonance, ultraviolet–visible, mass spectrometry, thermogravimetry–differential thermal analysis and magnetic susceptibility techniques. The optical features of Schiff base ligand and its metal complex compounds were compared for different solvents and molarities.