Thermomechanical Characterization And Modeling For TSV Structures

Continual scaling of devices and on-chip wiring has brought significant challenges for materials and processes beyond the 32-nm technology node in microelectronics. Recently, three-dimensional (3-D) integration with through-silicon vias (TSVs) has emerged as an effective solution to meet the future technology requirements. Among others, thermo-mechanical reliability is a key concern for the development of TSV structures used in die stacking as 3-D interconnects. This paper presents experimental measurements of the thermal stresses in TSV structures and analyses of interfacial reliability. The micro-Raman measurements were made to characterize the local distribution of the near-surface stresses in Si around TSVs. On the other hand, the precision wafer curvature technique was employed to measure the average stress and deformation in the TSV structures subject to thermal cycling. To understand the elastic and plastic behavior of TSVs, the microstructural evolution of the Cu vias was analyzed using focused ion beam (FIB) and electron backscattering diffraction (EBSD) techniques. Furthermore, the impact of thermal stresses on interfacial reliability of TSV structures was investigated by a shear-lag cohesive zone model that predicts the critical temperatures and critical via diameters.Microelectronics Research Cente

Nanoindentation Of Si Nanostructures: Buckling And Friction At Nanoscales

A nanoindentation system was employed to characterize mechanical properties of silicon nanolines (SiNLs), which were fabricated by an anisotropic wet etching (AWE) process. The SiNLs had the linewidth ranging from 24 nm to 90 nm, having smooth and vertical sidewalls and the aspect ratio (height/linewidth) from 7 to 18. During indentation, a buckling instability was observed at a critical load, followed by a displacement burst without a load increase, then a full recovery of displacement upon unloading. This phenomenon was explained by two bucking modes. It was also found that the difference in friction at the contact between the indenter and SiNLs directly affected buckling response of these nanolines. The friction coefficient was estimated to be in a range of 0.02 to 0.05. For experiments with large indentation displacements, irrecoverable indentation displacements were observed due to fracture of Si nanolines, with the strain to failure estimated to be from 3.8% to 9.7%. These observations indicated that the buckling behavior of SiNLs depended on the combined effects of load, line geometry, and the friction at contact. This study demonstrated a valuable approach to fabrication of well-defined Si nanoline structures and the application of the nanoindentation method for investigation of their mechanical properties at the nanoscale.Microelectronics Research Cente

Quantum Hall Ferromagnets

It is pointed out recently that the $\nu=1/m$ quantum Hall states in bilayer systems behave like easy plane quantum ferromagnets. We study the magnetotransport of these systems using their ``ferromagnetic" properties and a novel spin-charge relation of their excitations. The general transport is a combination of the ususal Hall transport and a time dependent transport with $quantized$ time average. The latter is due to a phase slippage process in $spacetime$ and is characterized by two topological constants. (Figures will be provided upon requests).Comment: 4 pages, Revtex, Ohio State Universit

Exclusive rare Bs→(K,η,η′)ℓ+ℓ−B_s\to (K,\eta,\eta')\ell^+\ell^- decays in the light-front quark model

Using the light-front quark model, we calculate the transition form factors, decay rates, and longitudinal lepton polarization asymmetries for the exclusive rare $B_s\to (K,\eta^{(\prime)})(\ell^+\ell^-,\nu_{\ell}\bar{\nu_{\ell}}$ ($\ell=e,\mu,\tau$) decays within the standard model, taking into account the $\eta-\eta'$ mixing angle. For the mixing angle $\theta=-20^{\circ}$ ($-10^{\circ}$) in the octet-singlet basis, we obtain ${\rm BR}(B_s\to \eta\sum\nu_{\ell}\bar{\nu}_{\ell})=1.1 (1.7)\times 10^{-6}$, ${\rm BR}(B_s\to \eta\mu^+\mu^-)=1.5 (2.4)\times 10^{-7}$, ${\rm BR}(B_s\to \eta\tau^+\tau^-)=3.8 (5.8)\times 10^{-8}$, ${\rm BR}(B_s\to \eta'\sum\nu_{\ell}\bar{\nu}_{\ell})=1.8 (1.3)\times 10^{-6}$, ${\rm BR}(B_s\to \eta'\mu^+\mu^-)=2.4 (1.8)\times 10^{-7}$, and ${\rm BR}(B_s\to \eta'\tau^+\tau^-)=3.4 (2.6)\times 10^{-8}$, respectively. The branching ratios for the $B_s\to K(\nu_{\ell}\bar{\nu_{\ell}},\ell^+\ell^-)$ decays are at least an order of magnitude smaller than those for the $B_s\to \eta^{(\prime)}(\nu_{\ell}\bar{\nu_{\ell}},\ell^+\ell^-)$ decays. The averaged values of the lepton polarization asymmetries for $B_s\to (K,\eta^{(\prime)})\ell^+\ell^-$ are obtained as \la P^K_L\ra_\mu=\la P^\eta_L\ra_\mu=\la P^{\eta'}_L\ra_\mu=-0.98, \la P^K_L\ra_\tau=-0.24, \la P^\eta_L\ra_\tau=-0.20 and \la P^{\eta'}_L\ra_\tau=-0.14, respectively.Comment: 20 pages, 6 figures, minor revision. version to appear in Journal of Physics