Optimization of DMOS Transistors for Smart Power Technologies by Simulation and Response Surface Methods

Abstract DMOS transistors for smart power technologies were investigated by extensive use of process and device simulation. For the task of simultaneously optimizing a multitude of parameters. experimental designs and response surface methods were used

In-Situ Nuclear Magnetic Resonance Investigation of Strain, Temperature, and Strain-Rate Variations of Deformation-Induced Vacancy Concentration in Aluminum

Critical strain to serrated flow in solid solution alloys exhibiting dynamic strain aging (DSA) or Portevin–LeChatelier effect is due to the strain-induced vacancy production. Nuclear magnetic resonance (NMR) techniques can be used to monitor in situ the dynamical behavior of point and line defects in materials during deformation, and these techniques are nondestructive and noninvasive. The new CUT-sequence pulse method allowed an accurate evaluation of the strain-enhanced vacancy diffusion and, thus, the excess vacancy concentration during deformation as a function of strain, strain rate, and temperature. Due to skin effect problems in metals at high frequencies, thin foils of Al were used and experimental results correlated with models based on vacancy production through mechanical work (vs thermal jogs), while in situ annealing of excess vacancies is noted at high temperatures. These correlations made it feasible to obtain explicit dependencies of the strain-induced vacancy concentration on test variables such as the strain, strain rate, and temperature. These studies clearly reveal the power and utility of these NMR techniques in the determination of deformation-induced vacancies in situ in a noninvasive fashion.

The problem of a metal impurity in an oxide: ab-initio study of electronic and structural properties of Cd in Rutile TiO2

In this work we undertake the problem of a transition metal impurity in an oxide. We present an ab-initio study of the relaxations introduced in TiO2 when a Cd impurity replaces substitutionally a Ti atom. Using the Full-Potential Linearized-Augmented-Plane-Wave method we obtain relaxed structures for different charge states of the impurity and computed the electric-field gradients (EFGs) at the Cd site. We find that EFGs, and also relaxations, are dependent on the charge state of the impurity. This dependence is very remarkable in the case of the EFG and is explained analyzing the electronic structure of the studied system. We predict fairly anisotropic relaxations for the nearest oxygen neighbors of the Cd impurity. The experimental confirmation of this prediction and a brief report of these calculations have recently been presented [P.R.L. 89, 55503 (2002)]. Our results for relaxations and EFGs are in clear contradiction with previous studies of this system that assumed isotropic relaxations and point out that no simple model is viable to describe relaxations and the EFG at Cd in TiO2 even approximately.Comment: 11 pages, 8 figures, Revtex 4, published in Physical Review

In situ NMR study of the two-phase equilibrium in Au-Al alloys.

It is shown that the Al-27 NMR spectrum in alpha-Au-xAl-alloys (x smaller than 15 at%) consists of two lines in the solidus - liquidus range. The analysis of the data leads to a new solidus line in the phase diagram of Au-Al

Increasing the robustness for reliable packages by prediction of delamination by cohesive zone element simulation

Robustness of a package is often proven by performing temperature cycling tests. Thermo-mechanical stress caused by the mismatch of coefficients of thermal expansion (CTE) and temperature variations remains a major concern for the reliability of semiconductor components. This issue is usually addressed by exposing the component to a certain number of cycles, followed by e.g. scanning acoustic microscopy (SAM) to investigate delamination. Discussions about specific cycling conditions, e.g. using -65°C/+175°C instead of -55°C/+150°C for the minimum and maximum temperatures of the cycles or even using liquid-liquid cycling instead of air to air to speed up investigations [1], are often moot, because no real understanding of the effect of the cycling conditions on the component is available