Journal of Electronic Materials

Barium (Ba)-incorporated strontium and magnesium-doped lanthanum aluminate, La0.9−xSr0.1BaxAl0.9Mg0.1O3−δ (LSBAM, with x = 0.00, 0.01 and 0.03) designated as LSBAM 00, LSBAM 01 and LSBAM 03, respectively, were effectively synthesized via citrate–nitrate-based auto-combustion method taking citric acid (C6H8O7·H2O) as a fuel agent. The electrical properties of the synthesized compositions were investigated as electrolyte for electrochemical applications. The powders were also characterized by simultaneous differential thermal analysis and thermogravimetric analysis to confirm the reaction temperature of the final product from the precursor. The X-ray Rietveld refinement patterns showed the rhombohedral structure with space group R-3c of the investigated systems. The scanning electron microscope images depicted fairly dense micrographs that are essential for a good electrolyte. The crystallite sizes were estimated to be in the range of 40 nm to 55 nm. The effect of doping has been investigated for the further improvement of ionic conducting efficiency of the systems. The electrical conductivity of the La0.9−xSr0.1BaxAl0.9Mg0.1O3−δ system has been measured at different temperatures between 400°C and 700°C to reveal the contribution of grains, grain boundaries and electrode specimen interface response to the total conductivity. The values of activation energy (Ea) for total conductivity suggest ionic conduction in the system that may primarily be due to the diffusion of O2− ions via oxygen vacancy sites. The conductivity for all compositions was found to increase with increasing temperature.

Structural, dielectric and electromagnetic properties of spinel ferrites Ni1 − xZnxFe2O4 have been reported in this study. Zinc substituted nickel ferrites Ni1 − xZnxFe2O4 (x = 0 to 1, Δx = 0.2) have been prepared with the sol gel citrate route with final sintering temperature of 1000°C for 8 h. The structural parameters of these ferrites are measured with the help of x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and Raman spectroscopy. The dielectric properties of the prepared ferrites have been measured with the help of an impedance analyzer and analyzed as a function of frequency in the MHz frequency range. The electromagnetic properties of these Ni-Zn ferrites in the X-band frequencies (8.2–12.4 GHz) have been obtained from the vector network analyzer (VNA) data. A study of reflection loss (RL) revealed that a minimum RL of − 17.54 dB is achieved at 9.62 GHz with matching thickness of 3.5 mm and absorption bandwidth of 3.108 GHz.

In the current study, the interfacial microstructures of Sn-Ag/Cu-X alloy (X = Ag, Sn or Zn) couples were investigated. The experimental results confirm that addition of Ag or Zn can effectively suppress the growth of the Cu3Sn layer, while addition of Sn accelerates the growth of the Cu3Sn layer. Meanwhile, the formation of voids is effectively suppressed by alloying the Cu substrate. The disappearance of voids and the absence of the Cu3Sn layer were well explained in terms of the phase diagram and the diffusion flux: the Cu3Sn phase is a nonequilibrium phase based on the Sn-Cu-Zn ternary phase diagram, since a high-Zn region is formed at the Cu6Sn5/Cu-Zn alloy interface; in addition, the high Sn diffusion flux in the Cu6Sn5 can suppress the growth of Cu3Sn and the formation of voids.

Solder joints used in electronic applications undergo reflow operations. Such operations can affect the solderability, interface intermetallic layer formation and the resultant solder joint microstructure. These in turn can affect the overall mechanical behavior of such joints. In this study the effects of reflow on solderability and mechanical properties were studied. Nanoindentation testing (NIT) was used to obtain mechanical properties from the non-reflow (as-melted) and multiple reflowed solder materials. These studies were carried out with eutectic Sn-3.5Ag solders, with or without mechanically added Cu or Ag reinforcements, using Cu substrates. Microstructural analysis was carried out on solder joints made with the same solders using copper substrate.

Dislocations in VPE GaP grown on (100) oriented LEC GaP substrates have been characterized, and their origins and effects on LED performance have been investigated. In non-nitrogen doped epilayers, the dislocations are found to originate in the substrate and propagate through the epilayers in straight lines in [100] and <211> directions. The dislocation density of the epilayer is found to be nearly equal to that of the substrate. Introduction of nitrogen during growth of the epilayer has been observed to bend these so-called “inclined≓ dislocations propagating through the layer into [0−1 1] directions in the (100) plane and thus produces segments of [0 −1 1] dislocations to relieve the lattice parameter mismatch due to N. The mismatch dislocation density is observed to be proportional to the N doping level. At very high N doping levels, > 1019 cm-3, a large number of new inclined dislocations are observed, which may be in part due to GaN precipitation. The effects of dislocations on LED properties were investigated by measuring dislocation densities in the individual diodes using the electron beam induced current mode of the SEM and comparing this with the spot brightness and luminous flux. The dislocations were observed to produce dark spots in the EL emission in many cases. For a series of runs where all growth and processing parameters were fixed, a good correlation between B/J and dislocation density was observed with B/J decreasing with increasing dislocation density in the range < 1 × 104 cm−2 to 1 × 106 cm−2.

Barium calcium titanate (Ba1-xCaxTiO3, BCTO) annealed under a flowing humid 2% hydrogen–argon gas mixture exhibits room-temperature persistent photoconductivity (PPC). The annealing atmosphere was chosen to produce substitutional hydrogen impurities that can be photoexcited, leading to the PPC phenomenon. The threshold photon energy for PPC in a BCTO crystal with x = 0.15 is 2.7 eV, lower than that for BaTiO3 and SrTiO3 (2.9 eV). A significant increase in mid-infrared absorption, attributed to free carriers, was correlated with a drop in electrical resistance. This effect showed persistence for several days at room temperature. Annealing the sample in air erased the PPC, indicating that the process is reversible.

To clarify potential issues that may arise in the future when high current densities are applied to joints in electronic power modules, high current density (25 kA/cm2) energization tests were conducted on sintered Ag joints sandwiched between Au and Ag layers. The degradation behavior differed depending on the current direction. The joint that placed the Au layer on the anode side showed a faster increase in voltage and temperature than the one placed on the Au layer at the cathode side, which also fractured at a much shorter energizing time (5 h). Generation and segregation of high-concentration coarse voids, in the same plane and growth of the Ag-Au solid solution layer, were observed in the sintered Ag layer of the joint, which placed the Au layer at the anode side before the fracture. Segregated voids existed near the cathode-side interface between the Ag layer and the surface of the base metal (Ti), and around the anode-side interface between the Ag layer and the Ag-Au solid solution layer. These results imply that the electromigration and diffusion coefficient imbalance between Ag and Au affect the behavior of the void generation and growth of the solid solution layer, which leads to a difference in the lifetime of the joints in the current direction under high current density energization. This indicates that the Au layer placed at the anode of the sintered Ag layer loses the reliability of the sintered Ag joints under the high current density driving electronic power modules.

Nanocrystalline Bi2Te3 films were deposited on (100) GaAs substrates using a modified metalorganic chemical vapor deposition (MOCVD) system, and the effect of growth parameters on the structural properties were investigated. The modified MOCVD system employed a mixing room for the formation of nanoparticles of Bi2Te3 by gas-phase reaction and a graphite susceptor for growth of nanoparticles on the substrate. The grown films contained many crystallites of nanosize, and large crystallites consisted of small particles a few tens of nanometer in size. This nanostructured film approach can be an economical way of producing high-performance thermoelectric films with nanostructure compared with other top-down methods.