3,628 research outputs found
Effects of Ion Atomic Number on Single-Event Gate Rupture (SEGR) Susceptibility of Power MOSFETs
The relative importance of heavy-ion interaction with the oxide, charge ionized in the epilayer, and charge ionized in the drain substrate, on the bias for SEGR failure in vertical power MOSFETs is experimentally investigated. The results indicate that both the charge ionized in the epilayer and the ion atomic number are important parameters of SEGR failure. Implications on SEGR hardness assurance are discussed
The role of stellar collisions for the formation of massive stars
We use direct N-body simulations of gas embedded star clusters to study the
importance of stellar collisions for the formation and mass accretion history
of high-mass stars. Our clusters start in virial equilibrium as a mix of gas
and proto-stars. Proto-stars then accrete matter using different mass accretion
rates and the amount of gas is reduced in the same way as the mass of stars
increases. During the simulations we check for stellar collisions and we
investigate the role of these collisions for the build-up of high-mass stars
and the formation of runaway stars. We find that a significant number of
collisions only occur in clusters with initial half-mass radii r_h < 0.1 pc.
After emerging from their parental gas clouds, such clusters end up too compact
compared to observed young, massive open clusters. In addition, collisions lead
mainly to the formation of a single runaway star instead of the formation of
many high mass stars with a broad mass spectrum. We therefore conclude that
massive stars form mainly by gas accretion, with stellar collisions only
playing a minor role if any at all. Collisions of stars in the pre-main
sequence phase might however contribute to the formation of the most massive
stars in the densest star clusters and possibly to the formation of
intermediate-mass black holes with masses up to a few 100 Msun.Comment: 10 pages, 8 figures, MNRAS in pres
Numerical modeling of the multi-stage Stern\unicode{x2013}Gerlach experiment by Frisch and Segr\`e using co-quantum dynamics via the Schr\"odinger equation
We use a theory termed co-quantum dynamics (CQD) to numerically model spin
flip in the multi-stage Stern\unicode{x2013}Gerlach (SG) experiment conducted
by R. Frisch and E. Segr\`e. This experiment consists of two
Stern\unicode{x2013}Gerlach apparatuses separated by an inner rotation
chamber that varies the fraction of spin flip. To this day, quantum mechanical
treatments inadequately predict the Frisch\unicode{x2013}Segr\`e experiment.
Here, we account for electron-nuclear interactions according to CQD and solve
the associated Schr\"odinger equation. Our simulation outcome agrees with the
Frisch\unicode{x2013}Segr\`e experimental observation and supports CQD as a
potential model for electron spin evolution and collapse.Comment: 13 pages, 3 figure
Single Event Effects in the Pixel readout chip for BTeV
In future experiments the readout electronics for pixel detectors is required
to be resistant to a very high radiation level. In this paper we report on
irradiation tests performed on several preFPIX2 prototype pixel readout chips
for the BTeV experiment exposed to a 200 MeV proton beam. The prototype chips
have been implemented in commercial 0.25 um CMOS processes following radiation
tolerant design rules. The results show that this ASIC design tolerates a large
total radiation dose, and that radiation induced Single Event Effects occur at
a manageable level.Comment: 15 pages, 6 Postscript figure
Radiation and magnetic field effects on new semiconductor power devices for HL-LHC experiments
The radiation hardness of commercial Silicon Carbide and Gallium Nitride
power MOSFETs is presented in this paper, for Total Ionizing Dose effects and
Single Event Effects, under gamma, neutrons, protons and heavy ions. Similar
tests are discussed for commercial DC-DC converters, also tested in operation
under magnetic field
Numerical modeling of the multi-stage Stern\unicode{x2013}Gerlach experiment by Frisch and Segr\`e using co-quantum dynamics via the Bloch equation
We numerically study the spin flip in the Frisch\unicode{x2013}Segr\`e
experiment, the first multi-stage Stern\unicode{x2013}Gerlach experiment,
within the context of the novel co-quantum dynamics theory. We model the middle
stage responsible for spin rotation by sampling the atoms with the Monte Carlo
method and solving the dynamics of the electron and nuclear magnetic moments
numerically according to the Bloch equation. Our results show that, without
using any fitting parameters, the co-quantum dynamics closely reproduces the
experimental observation reported by Frisch and Segr\`e in 1933, which has so
far lacked theoretical predictions.Comment: 9 pages, 6 figure
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Mechanisms of heavy-ion induced gate rupture in thin oxides
Single event gate rupture (SEGR) is a catastrophic failure mode that occurs in dielectric materials that are struck by energetic heavy ions while biased under a high electric field condition. SEGR can reduce the critical electric field to breakdown to less than half the value observed in normal voltage ramp reliability tests. As electric fields in gate oxides increase to greater than 5 MV/cm in advanced MOS technologies, the impact of SEGR on the reliability of space based electronics must be assessed. In this summary, the authors explore the nature of SEGR in oxides with thickness from 7 nm to less than 5 nm, where soft breakdown is often observed during traditional reliability tests. They discuss the possible connection between the present understanding of SEGR and voltage stress breakdown models
Single-Event Gate Rupture in Power MOSFETs: A New Radiation Hardness Assurance Approach
Almost every space mission uses vertical power metal-semiconductor-oxide field-effect transistors (MOSFETs) in its power-supply circuitry. These devices can fail catastrophically due to single-event gate rupture (SEGR) when exposed to energetic heavy ions. To reduce SEGR failure risk, the off-state operating voltages of the devices are derated based upon radiation tests at heavy-ion accelerator facilities. Testing is very expensive. Even so, data from these tests provide only a limited guide to on-orbit performance. In this work, a device simulation-based method is developed to measure the response to strikes from heavy ions unavailable at accelerator facilities but posing potential risk on orbit. This work is the first to show that the present derating factor, which was established from non-radiation reliability concerns, is appropriate to reduce on-orbit SEGR failure risk when applied to data acquired from ions with appropriate penetration range. A second important outcome of this study is the demonstration of the capability and usefulness of this simulation technique for augmenting SEGR data from accelerator beam facilities. The mechanisms of SEGR are two-fold: the gate oxide is weakened by the passage of the ion through it, and the charge ionized along the ion track in the silicon transiently increases the oxide electric field. Most hardness assurance methodologies consider the latter mechanism only. This work demonstrates through experiment and simulation that the gate oxide response should not be neglected. In addition, the premise that the temporary weakening of the oxide due to the ion interaction with it, as opposed to due to the transient oxide field generated from within the silicon, is validated. Based upon these findings, a new approach to radiation hardness assurance for SEGR in power MOSFETs is defined to reduce SEGR risk in space flight projects. Finally, the potential impact of accumulated dose over the course of a space mission on SEGR susceptibility is explored. SEGR evaluation of gamma-irradiated power MOSFETs suggests a non-significant SEGR susceptibility enhancement due to accumulated dose from gamma rays. During SEGR testing, an unexpected enhanced dose effect from heavy-ion irradiation was detected. We demonstrate that this effect could be due to direct ionization by two or more ions at the same channel location. The probability on-orbit for such an occurrence is near-zero given the low heavy-ion fluence over a typical mission lifetime, and did not affect SEGR susceptibility. The results of this work can be used to bound the risk of SEGR in power MOSFETs considered for insertion into spacecraft and instruments
The Tenth Article of Ettore Majorana
This year is the centenary of the birth of Ettore Majorana, one of the major
Italian physicists of all times. In this note we briefly sketch a few
biographical details about Ettore Majorana and introduce and discuss the main
points of Majorana's 10th article. In his article Majorana explicitly considers
quantum mechanics as an irreducible statistical theory because the theory is
not able to describe the time evolution of a single particle or atom in a
precise environment at a deterministic level. This lack of determinism at the
level of an elementary physical system motivated him to suggest a formal
analogy between statistical laws observed in physics and in the social
sciences. We hope the occasion of the centenary of the birth of Ettore Majorana
will be useful to remember and to reconsider not only his exceptional
achievements in theoretical physics but also his fresh and original views on
the role of statistical laws in physics and in other disciplines such as the
social sciences.Comment: 3 pages, to appear in Europhysics News 37/4 July/August 200
The influence of gas expulsion and initial mass-segregation on the stellar mass-function of globular star clusters
Recently de Marchi, Paresce & Pulone (2007) studied a sample of twenty
globular clusters and found that all clusters with high concentrations have
steep stellar mass-functions while clusters with low concentration have
comparatively shallow mass-functions. No globular clusters were found with a
flat mass-function and high concentration. This seems curious since more
concentrated star clusters are believed to be dynamically more evolved and
should have lost more low-mass stars via evaporation, which would result in a
shallower mass-function in the low-mass part.
We show that this effect can be explained by residual-gas expulsion from
initially mass-segregated star clusters, and is enhanced further through
unresolved binaries. If gas expulsion is the correct mechanism to produce the
observed trend, then observation of these parameters would allow to constrain
cluster starting conditions such as star formation efficiency and the
time-scale of gas expulsion.Comment: accepted for publication in MNRAS, 10 pages, 6 figure
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