Mechanical ball shear, electromigration, and thermal cycling reliability testing on novel solder interconnects of highly integrated chips for advanced applications

In the near future, Ultra Large Scale Integrated Circuits (ULSI) with high integration has drawn the huge attention because of its potential applications in VR, AI, IoTs and automotive regions. Thermal budget and reliability concerns are two major issues that are urgently needed to be solved for these technologies. Since the increasing integration of ICs might lead to low yield concern, low fabrication temperature is expected to reduce the thermal impact on ICs properties. Besides, better reliability is also required to the electric devices for those to work under harsh outdoor environments. This study is tended to be focused on the novel solder bonds for the advanced ICs, including low temperature solder, Cu-core solder ball, and their response under various reliability tests. Three main reliability tests: (1) ball shear test, (2) electromigration test (EM) and (3) thermal cycling test (TCT), are conducted to evaluate the reliability of solder bonds. In this work, the novel Bi-40In solder alloy with improved mechanical property and the EM-resisted Cu-core solder ball are demonstrated. The re-designed low temperature solder joint reveals the superior ball shear strength than that of conventional eutectic Bi-33In joint. Additionally, the interconnects using Cu-core solder ball show the high resistance against EM under current stressing. Regarding TCT, the assemble joints with various grain structures are tested to realize the effects of Sn grain size on joint degradation and the possible ways for relieving the thermomechanical stress caused by TCT. The microstructure, elemental characteristics and grain structure are analyzed by FE-SEM, FE-EPMA and EBSD, respectively. The failure mechanisms for all reliability tests are addressed and discussed in details as well

Enhanced electrocatalytic activity of Au@Cu core@shell nanoparticles towards CO2 reduction

The development of technologies for the recycling of carbon dioxide into carbon-containing fuels is one of the major challenges in sustainable energy research. Two of the main current limitations are the poor efficiency and fast deactivation of catalysts. Core–shell nanoparticles are promising candidates for enhancing challenging reactions. In this work, Au@Cu core–shell nanoparticles with well-defined surface structures were synthesized and evaluated as catalysts for the electrochemical reduction of carbon dioxide in neutral medium. The activation potential, the product distribution and the long term durability of this catalyst were assessed by electrochemical methods, on-line electrochemical mass spectrometry (OLEMS) and on-line high performance liquid chromatography. Our results show that the catalytic activity and the selectivity can be tweaked as a function of the thickness of Cu shells. We have observed that the Au cubic nanoparticles with 7–8 layers of copper present higher selectivity towards the formation of hydrogen and ethylene; on the other hand, we observed that Au cubic nanoparticles with more than 14 layers of Cu are more selective towards the formation of hydrogen and methane. A trend in the formation of the gaseous products can be also drawn. The H2 and CH4 formation increases with the number of Cu layers, while the formation of ethylene decreases. Formic acid was the only liquid species detected during CO2 reduction. Similar to the gaseous species, the formation of formic acid is strongly dependent on the number of Cu layers on the core@shell nanoparticles. The Au cubic nanoparticles with 7–8 layers of Cu showed the largest conversion of CO2 to formic acid at potentials higher than 0.8 V vs. RHE. The observed trends in reactivity and selectivity are linked to the catalyst composition, surface structure and strain/electronic effects

Magnetic properties in a partially oxidized nanocomposite of Cu-CuCl

Magnetism of a very thin antiferromagnetic (AFM) surface CuO has been investigated with the partially oxidized nanocomposites of Cu-CuCl, ~ 200 nm. The samples are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, X-ray-excited Auger electron spectroscopy, transmission electron microscope and magnetic measurements. The characterizations indicate that the composites have a core-shell structure. Before the oxidation, it is (Cu)core/(CuCl)shell, and after the oxidation, (Cu)core/(Cu2O+CuCl+minuteCuO)shell. The magnetic measurements have revealed that a ferromagnetic (FM) like open hysteresis exists at the temperature below the freezing point, TF. In the high field region, a paramagnetic (PM) response appears without showing a sign of saturation. Also, the field dependent magnetization (M-H) measurement is PM-like at T > TF. These interesting magnetic properties are evident to arise from the AFM CuO on the outer surface. They are attributed to the uncompensated surface spins of Cu2+ and the effect of surface random potential. More interestingly, the magnetic susceptibility is greatly enhanced in the presence of Cl- anions at T < TF, according to the field-cooled/zero-field-cooled (FC/ZFC) measurements. This further supports the point that the disorder or frustration effect of the impurity would reduce the AFM ordering of CuO and increase the level of uncompensated spins.Comment: 8 pages including 7 figures, Nanotechnology In Pres

Thermal conductivity and stability of commercial MgB2_2 conductors

This paper presents a study of the thermal transport properties of MgB$_2$ tapes differing in architecture, stabilization and constituent materials. The temperature and field dependence of thermal conductivity, $\kappa(T,B)$, was investigated both along the conductor and in the direction perpendicular to the tape. These data provide fundamental input parameters to describe the 3D heat diffusion process in a winding. Thermal transport properties - even in field - are typically deduced using semi-empirical formulas based on the residual resistivity ratio of the stabilizer measured in absence of magnetic field. The accuracy of these procedures was evaluated comparing the calculated $\kappa$ values with the measured ones. Based on the experimental thermal conduction properties $\kappa(T,B)$ and critical current surface $J_C(T,B)$ we determined the dependence of minimum quench energy and normal zone propagation velocity on the operating parameters of the conductor. The correlation between thermal properties and tape layout allowed us to provide information on how to optimize the thermal stability of MgB$_2$ conductors.Comment: Accepted for publication in Superconductor Science and Technolog

Magnetic force microscopy investigation of arrays of nickel nanowires and nanotubes

The magnetic properties of arrays of nanowires (NWs) and nanotubes (NTs), 150 nm in diameter, electrodeposited inside nanoporous polycarbonate membranes are investigated. The comparison of the nanoscopic magnetic force microscopy (MFM) imaging and the macroscopic behavior as measured by alternating gradient force magnetometry (AGFM) is made. It is shown that MFM is a complementary technique that provides an understanding of the magnetization reversal characteristics at the microscopic scale of individual nanostructures. The local hysteresis loops have been extracted by MFM measurements. The influence of the shape of such elongated nanostructures on the dipolar coupling and consequently on the squareness of the hysteresis curves is demonstrated. It is shown that the nanowires exhibit stronger magnetic interactions than nanotubes. The non-uniformity of the magnetization states is also revealed by combining the MFM and AGFM measurements.Comment: 7 pages, 5 figure

Targeted cooling with CVD diamond and micro-channel to meet 3-D IC heat dissipation challenge

Thermal simulation of a stack consists of three IC layers bonded “face up” is performed. It is shown that by inserting electrically isolated thermal through silicon via (TTSV) having Cu core and CVD diamond as a liner shell that extends across the layers to substrate, significant temperature reduction up to (103K) 62% can be achieved which also reflected through almost 60% reduction in thermal resistivity. Additionally simple microchannel integration with IC 3 layer and allowed fluid flow through the channel show transient temperature reduction. TTSV is also shown to be effective in mitigating severe heat dissipation issue facing 3-D IC bonded “face down” and logic layer stacked on memory substrate

Is graphene on copper doped?

Angle-resolved photoemission spectroscopy (ARPES) and X-ray photoemission spectroscopy have been used to characterise epitaxially ordered graphene grown on copper foil by low-pressure chemical vapour deposition. A short vacuum anneal to 200 °C allows observation of ordered low energy electron diffraction patterns. High quality Dirac cones are measured in ARPES with the Dirac point at the Fermi level (undoped graphene). Annealing above 300 °C produces n-type doping in the graphene with up to 350 meV shift in Fermi level, and opens a band gap of around 100 meV. Dirac cone dispersion for graphene on Cu foil after vacuum anneals (left: 200 °C, undoped; right: 500 °C, n-doped). Centre: low energy electron diffraction from graphene on Cu foil after 200 °C anneal. Data from Antares (SOLEIL)

Adlayer core-level shifts of admetal monolayers on transition metal substrates and their relation to the surface chemical reactivity

Using density-functional-theory we study the electronic and structural properties of a monolayer of Cu on the fcc (100) and (111) surfaces of the late 4d transition metals, as well as a monolayer of Pd on Mo bcc(110). We calculate the ground states of these systems, as well as the difference of the ionization energies of an adlayer core electron and a core electron of the clean surface of the adlayer metal. The theoretical results are compared to available experimental data and discussed in a simple physical picture; it is shown why and how adlayer core-level binding energy shifts can be used to deduce information on the adlayer's chemical reactivity.Comment: RevTeX, 7 pages, 2 figure

Calculation of the positron bound state with the copper atom

A new relativistic method for calculation of positron binding to atoms is presented. The method combines a configuration interaction treatment of the valence electron and the positron with a many-body perturbation theory description of their interaction with the atomic core. We apply this method to positron binding by the copper atom and obtain the binding energy of 170 meV (+ - 10%). To check the accuracy of the method we use a similar approach to calculate the negative copper ion. The calculated electron affinity is 1.218 eV, in good agreement with the experimental value of 1.236 eV. The problem of convergence of positron-atom bound state calculations is investigated, and means to improve it are discussed. The relativistic character of the method and its satisfactory convergence make it a suitable tool for heavier atoms.Comment: 15 pages, 5 figures, RevTe