A Technical Note on Quantum Dots for Multi-Color Fluorescence in situ Hybridization

Quantum dots (Qdots) are semiconductor nanocrystals, which are photo-stable, show bright fluorescence with narrow, symmetric emission spectra and are available in multiple resolvable colors. We established a FISH protocol for the simultaneous visualization of up to 6 different DNA probes differentially labeled with Qdots and with conventional organic fluorochromes. Using a Leica SP5 laser scanning confocal microscope for image capture, we tested various combinations of hapten-labeled probes detected with streptavidin-Qdot525, sheep anti-digoxigenin-Qdot605, rat anti-dinitrophenyl-Qdot655 and goat anti-mouse-Qdot655, respectively, together with FITC-dUTP-, Cy3-dUTP- and Texas Red-dUTP-labeled probes. We further demonstrate that Qdots are suitable for imaging of FISH probes using 4Pi microscopy, which promises to push the resolution limits of light microscopy to 100 nanometers or less when applying a deconvolution algorithm, but requires the use of highly photo-stable fluors. Copyright (C) 2009 S. Karger AG, Base

Investigation of Vector Discretization Schemes for Box Volume Methods

ABSTRACT The application of the box integration method in Technology CAD environments is investigated. A particular difficulty arises from physical models like the impact ionization rate or the high-field mobility within the drift-diffusion carrier transport equations which rely on vector quantities. We discuss different methods how generation rates can be approximated in the box scheme and how the requirements for the applied vector discretizations are. Simulation results of devices operated near break-down are presented using implementations of the presented schemes. Advantages and disadvantages in respect to implementation, to errors, and to convergence behavior are presented

Role of hydrogen in volatile behaviour of defects in SiO2-based electronic devices

Charge capture and emission by point defects in gate oxides of metal–oxide–semiconductor field-effect transistors (MOSFETs) strongly affect reliability and performance of electronic devices. Recent advances in experimental techniques used for probing defect properties have led to new insights into their characteristics. In particular, these experimental data show a repeated dis- and reappearance (the so-called volatility) of the defect-related signals. We use multiscale modelling to explain the charge capture and emission as well as defect volatility in amorphous SiO2 gate dielectrics. We first briefly discuss the recent experimental results and use a multiphonon charge capture model to describe the charge-trapping behaviour of defects in silicon-based MOSFETs. We then link this model to ab initio calculations that investigate the three most promising defect candidates. Statistical distributions of defect characteristics obtained from ab initio calculations in amorphous SiO2 are compared with the experimentally measured statistical properties of charge traps. This allows us to suggest an atomistic mechanism to explain the experimentally observed volatile behaviour of defects. We conclude that the hydroxyl-E′ centre is a promising candidate to explain all the observed features, including defect volatility

Origin of trap assisted tunnelling in ammonia annealed SiC trench MOSFETs

The interface between silicon carbide (SiC) and silicon dioxide (SiO2) is of considerable importance for the performance and reliability of 4H-SiC (trench) metal oxide semiconductor field effect transistors (MOSFETs) and various different post oxidation anneals (POAs) have been used to optimize its quality. Whereas nitric oxide (NO) POA leads to very reliable and well performing MOSFETs, ammonia (NH3) can further improve the device performance, however, at the cost of the gate oxide (GOX) reliability, e.g. leading to trap assisted tunneling (TAT). We investigate the origin of TAT and GOX leakage in differently annealed gate oxides experimentally, using 4H-SiC trench MOSFETs, and theoretically, using Density Functional Theory (DFT) simulations. Our findings reinforce the view that the NO anneal for SiC devices results in the best overall quality as devices annealed in NH3 and nitrogen N2 show higher oxide charge density and leakage currents. DFT simulations demonstrate that, contrary to what has often been assumed so far, NH3 annealing leads to the formation of additional hydrogen related defects, which open leakage paths in the oxide otherwise not present in NO treated oxides

Logarithmic behavior of degradation dynamics in metal--oxide semiconductor devices

In this paper the authors describe a theoretical simple statistical modelling of relaxation process in metal-oxide semiconductor devices that governs its degradation. Basically, starting from an initial state where a given number of traps are occupied, the dynamics of the relaxation process is measured calculating the density of occupied traps and its fluctuations (second moment) as function of time. Our theoretical results show a universal logarithmic law for the density of occupied traps $\bar{} \sim \phi (T,E_{F}) (A+B \ln t)$, i.e., the degradation is logarithmic and its amplitude depends on the temperature and Fermi Level of device. Our approach reduces the work to the averages determined by simple binomial sums that are corroborated by our Monte Carlo simulations and by experimental results from literature, which bear in mind enlightening elucidations about the physics of degradation of semiconductor devices of our modern life

Lehrbezogenes Wissensmanagement: Relevanz, Prozesse, Herausforderungen und Potenziale [Poster]

„Lehrbezogenes Wissensmanagement ist die Gesamtheit der personalen, organisatorischen und technischen Praktiken, die auf die systematische, effiziente und nachhaltige Nutzung von Wissen im Kontext Lehre zielen. Dies umfasst die zielgerichtete Identifikation, den Erwerb, die Entwicklung, die Verteilung, die Nutzung, die Bewahrung und Bewertung von lehrbezogenem Wissen (u.a. hochschuldidaktisches oder fachwissenschaftliches Wissen)“ (Siegel, Krummenauer-Grasser und Stahl, i.V.)

A numerical study of partial-SOI LDMOSFETs

Abstract The high-voltage and self-heating behavior of partial-SOI (silicon-on-insulator) LDMOSFETs were studied numerically. Different locations of the silicon window were considered to investigate the electrical and thermal effects. It is found that the potential distribution of the partial-SOI LDMOSFET with the silicon window under the drain is similar to that of standard junction isolation devices. With the silicon window under the source the potential distribution is similar to that of the conventional SOI LDMOSFET. Using the two-dimensional numerical simulator MINIMOS-NT, we confirm that the breakdown voltage of partial-SOI LDMOSFETs with a silicon window under the source is higher than that of partial-SOI LDMOSFET with a silicon window under the drain

Effect of electric field on migration of defects in oxides: Vacancies and interstitials in bulk MgO

Dielectric layers composed of metal oxides are routinely subjected to external electric fields during the course of normal operation of electronic devices. Many phenomenological theories suggest that electric fields strongly affect the properties and mobilities of defects in oxide films and can even facilitate the creation of new defects. Although defects in metal oxides have been studied extensively both experimentally and theoretically, the effect of applied electric fields on their structure and migration barriers is not well understood and still remains subject to speculations. Here, we investigate how static, homogeneous electric fields affect migration barriers of canonical defects—oxygen vacancies and interstitial ions—in a prototypical oxide, MgO. Using the modern theory of polarization within density functional theory (DFT), we apply electric fields to defect migration pathways in three different charge states. The effect of the field is characterized by the change of the dipole moment of the system along the migration pathway. The largest changes in the calculated barriers are observed for charged defects, while those for the neutral defects are barely significant. We show that by multiplying the dipole moment difference between the initial and the transition states, which we define as the effective dipole moment, by the field strength, one can obtain an estimate of the barrier change in excellent agreement with the DFT calculated values. These results will help to assess the applicability of phenomenological models and elucidate linear and nonlinear effects of field application in degradation of microelectronic devices, electrocatalysis, batteries, and other applications