Microstructure evolution of the Sn–Ag–y%Cu interconnect

The lead free Sn–Ag–y%Cu (y = 0.0, 0.5, 1.0 and 2.0) interconnect interfacial microstructures and the microstructure evolution under thermal treatment (isothermal aging, 150 °C/1000 h) were studied in detail by using surface microetching microscopy and cross section microscopy. The corresponding mechanical and reliability behaviors were evaluated by performing shear test and fracture mode analysis before and after the thermal treatment. The results indicate: (i) The interconnects could have different microstructures and intermetallic compound (IMC), depending on the Cu content. The Cu–Sn IMC could have microstructures that were clusters or protrusion-like, Augustine grass leaf-like, scissor-like, tweezers-like, etc. (ii) Ag₃Sn IMCs were not observed at time zero for any interconnect groups, but they occurred after the aging for all groups. The Ag₃Sn IMC could have different microstructures, again depending on Cu content. For low Cu content, the Ag₃Sn IMCs were granules or nodules; for higher Cu content, Ag₃Sn IMCs were plate-like. (iii) The growth of Ag₃Sn plates was promoted by the growth of Cu–Sn IMCs, but indirectly linked to the Cu content. (iv) High Cu content (1.0 wt% and higher) could degrade the mechanical and reliability performances of the LF interconnect by providing a brittle joint, which was mainly achieved through the substantial growth of Cu–Sn IMCs and Ag₃Sn plates.     

Photoconductivity and photoluminescence under bias in GaInNAs/GaAs MQW p-i-n structures

The low temperature photoluminescence under bias (PLb) and the photoconductivity (PC) of a p-i-n GaInNAs/GaAs multiple quantum well sample have been investigated. Under optical excitation with photons of energy greater than the GaAs bandgap, PC and PLb results show a number of step-like increases when the sample is reverse biased. The nature of these steps, which depends upon the temperature, exciting wavelength and intensity and the number of quantum wells (QWs) in the device, is explained in terms of thermionic emission and negative charge accumulation due to the low confinement of holes in GaInNAs QWs. At high temperature, thermal escape from the wells becomes much more dominant and the steps smear out.     

Optical gain in 1.3-μm electrically driven dilute nitride VCSOAs

We report the observation of room-temperature optical gain at 1.3 μm in electrically driven dilute nitride vertical cavity semiconductor optical amplifiers. The gain is calculated with respect to injected power for samples with and without a confinement aperture. At lower injected powers, a gain of almost 10 dB is observed in both samples. At injection powers over 5 nW, the gain is observed to decrease. For nearly all investigated power levels, the sample with confinement aperture gives slightly higher gain.     

Solid-liquid reactions: The effect of Cu content on Sn-Ag-Cu interconnects

The impact of copper content on the Sn-Ag-y%Cu (Ag=constant=3.5; y=0.0, 0.5, 1.0, and 2.0) interconnects was investigated in this study. The copper content and solid-liquid (S-L) reactions were used as inputs, and the outputs were the interfacial microstructure evolution and joint macro-performance. Surface microetching microscopy, cross-section microscopy, energy-dispersive x-ray analysis, shear test, and differential scanning calorimetry were used in the studies. It was discovered that as-soldered Sn-Ag-y%Cu interconnects could have different interfacial microstructures depending on copper content; no Ag₃Sn plates were observed for any alloy groups. After the S-L reactions, Ag₃Sn plates occurred for all groups. The magnitude of the Ag₃Sn plate growth depended on copper content. This and other effects of copper content on Sn-Ag-Cu interconnects are discussed in this article.     

Thermal loading of a thin layer with circular debonding over a substrate

By using techniques appropriate to mixed boundary value problems, this study addresses the determination of stress intensity factors for a circular interface debonding between a thin layer and a substrate subjected to nearly uniform temperature change. The solution method involves three-dimensional equilibrium equations of thermo-elasticity under axisymmetry conditions. The stress intensity factors are obtained by solving the resulting pair of coupled singular integral equations numerically. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photoluminescence in n and p modulation-doped GaInNAs/GaAs quantum wells

Experimental results concerning the steady-state photoluminescence (PL) studies in n and p modulation doped and undoped GaInNAs/GaAs quantum wells are presented. The effects of modulation, type of doping and nitrogen concentration on the PL and the temperature dependence of the band gap, carrier localization and non-radiative recombination are investigated. Increasing the nitrogen composition decreases energy band gap as expected. The n-type modulation doping eliminates most of the defect-related effects and blue shifts the energy band gap. However, the p-type doping gives rise to additional features in the PL spectra and red shifts energy band gap further compared to the n-type-doped material.     

Economic and cross-media effect analyses of best available techniques for caustic recovery from mercerization textile wastewater

Clean Technologies and Environmental Policy - Caustic can be recovered from textile mercerization wastewaters by evaporation or membrane filtration. The main objective of this study was to evaluate...     

The effect of deposition on electrochemical impedance properties of TiO<Subscript>2</Subscript>/FTO photoanodes

The integration of TiO₂ layers onto a substrate is challenging and limits the application potential of TiO₂. Even though, several studies have been reported to solve this problem by applying various deposition methods, there is still lack of information about how these methods affect the electrochemical and photo-electrochemical properties of resulting electrodes. The TiO₂ layers possessing different morphologies, deposited on the conductive FTO glass by means of various different deposition techniques (dip-coating, electrospinning and electrospraying), were used as photoanode (and working electrode) in the three-compartment electrochemical cell. The TiO₂ electrodes were calcinated at 450 °C and after that all samples revealed the crystallographic form of anatase. Using these three deposition techniques, three different morphologies were obtained. They consisted of a thin TiO₂ nanoparticle layer, TiO₂ nanoparticle/nanofiber layer and TiO₂ nanorod layer, respectively. The crystallinity and surface properties of the calcinated layers were determined by XRD, Raman spectroscopy, FTIR-ATR and SEM analyses. The electrochemical impedance (EIS) and photo-induced properties of photoanodes were studied by electrochemical measurements. The effects of surface morphology and crystal size of nanostructured layers on electrochemical impedance and photo-electrochemical properties were investigated. The electrodes prepared by dip-coating technique showed the best electrochemical impedance and photo-electrochemical results compared to other two types of electrodes. Dip-coating TiO₂ layer possesses the biggest crystal size and lowest charge transfer resistance which result the highest photocurrent density.     

Gain studies of 1.3-μm dilute nitride HELLISH-VCSOA for optical communications

The hot electron light emitting and lasing in semiconductor heterostructure-vertical-cavity semiconductor optical amplifier (HELLISH-VCSOA) device is based on Ga_0.35In_0.65 N_0.02As_0.08/GaAs material for operation in the 1.3-μm window of the optical communications. The device has undoped distributed Bragg reflectors (DBRs). Therefore, problems such as those associated with refractive index contrast and current injection, which are common with doped DBRs in conventional VCSOAs, are avoided. The gain versus applied electric field curves are measured at different wavelengths using a tunable laser as the source signal. The highest gain is obtained for the 1.3-μm wavelength when an electric field in excess of 2 kV/cm is applied along the layers of the device.     

Hot phonons and instabilities in GaAs/GaAlAs structures

We report experimental observations concerning high field parallel transport in GaAs/GaAlAs quantum-well structures comparing degenerate and non-degenerate material. Hot electron photoluminescence measurements show hot-phonon reduction of the energy relaxation rates in degenerate material as compared with that in non-degenerate material in agreement with a simple model of transport involving hot phonon effects. The latter predicts a reduction in drift velocity at high fields compared with that in bulk material and this is observed in our specimens. Hot phonons are shown to inhibit instabilities. Non degenerate samples exhibit current instabilities much more readily than degenerate material. In the latter, the hot phonon reduction in drift velocity will tend to inhibit NDR via real space transfer or via intervalley transfer.