1,721,114 research outputs found
Instabilities in Silicon Power Devices: A Review of Failure Mechanisms in Modern Power Devices
No full textUnclamped repetitive stress on 1200 V normally-off SiC JFETs
No full textAn experimental characterization of new-generation normally-off vertical channel 1200 V SiC JFETs
under unclamped repetitive stress (URS) is presented. The drain and gate leakage currents are monitored,
and their time evolution is recorded.
The degradation of the leakage characteristics has been compared with repeated short circuits tests, at
the same stress energy, thus demonstrating that different mechanisms take place in these conditions.
Furthermore, a post-failure analysis of the surface of the device by means of a optic microscope indicates
that a termination weakness could be the major cause for the device leakage increment and consequent
failure
IGBT RBSOA non-destructive testing methods: Analysis and discussion
No full textThe investigation about RBSOA limits and the study of the instabilities in high power IGBT devices, during clamped and unclamped operations can be executed by means of non-destructive experimental test circuits where the power device is switched in the presence of a protection circuit able to save it in the case of a dangerous condition to take place. This work, starting from the main non-destructive tester (NDT) proposed during the past years, supplies critical considerations and discussions about the main problems and difficulties that arise when a non-destructive experimental set-up is used for the IGBT RBSOA characterization. The authors demonstrate that the characteristics of the protection circuit must be chosen accordingly to the device that must be characterized and the possibility of saving this device may be significantly improved by a proper choice of the circuit parameters. Considerations about the influence of the parasitic stray elements in the circuit operation and the possible solutions to these problems are also investigated
Operation of SiC normally-off JFET at the edges of its safe operating area
No full textThe paper presents the results of an experimental characterization about the operation of the last generation normally-off SiC JFETs at the edges of their safe operating area. Short circuit and unclamped turn-off operations have been investigated by means of a nondestructive experimental set up where the device is switched in the presence of a protection circuit capable of limiting the energy dissipated on the device after the failure occurrence. The experimental results confirm the very good performances of the device in short circuit for which the failure can be associated only to the increase of the temperature over the limits imposed by the surface metallization. A different scenario appears for the unclamped tests where a second breakdown occurs after a quite long avalanche phase followed by the device failure. It is demonstrated that the duration of the avalanche phase depends on the temperature of the device under test. The damaged area after an avalanche failure is localized at the edge termination of the device and, in particular, at the corner between source and gate metallization
Mechanoluminescence of nylon under high velocity impact
Full text linkThe light emissions produced during deformation of solids induced by any mechanical action is called mechanoluminescence (ML). This phenomenon was reported mostly in hypervelocity impacts. Using high speed video-recording, the authors found evidence of ML for nylon at much lower impact velocity (of the order of 100 m/s). In order to understand the mechanism responsible for ML, Taylor impact experiments were planned and performed. Several impact configurations were investigated: Taylor anvil impact, Taylor impact on nylon anvil and rod-on-rod impact experiment. During the tests, the emitted light was measured using a wide-spectrum visible-to-infrared photodiode with response below 1 microsecond, and the signals were analyzed. The existence of a limiting impact velocity below which ML is no longer observed seems to be indicative of the fact that ML is controlled by the high pressure that is generated under uniaxial strain loading conditions. This result is consistent with the fact that, as soon as the compressive stress wave travels longitudinally in the Taylor sample and the pressure drops as a result of the arrival of the release waves, the ML no longer occurs. When tests were repeated in vacuum, no light emission in the visible range was observed. This finding seems to indicate that light emission occurs as a result of the oxidation of free radicals generated by the rupture of the polymer chains caused by the dynamic pressure wav
Behavior of power MOSFETs during heavy ions irradiation performed after γ-rays exposure
No full textThe behavior of medium voltage commercial power MOSFETs, first degraded with increasing c-rays doses
and subsequently irradiated with heavy ions, is presented. It is shown that the degradation of the gate
oxide caused by the c irradiation severely corrupt the SEE robustness and drastically modify the physical
behavior of the device under test after the impact of a heavy ion. A decrease of the critical voltages at
which destructive burnouts and gate ruptures appear has been detected in all devices previously irradiated
with c-rays, the amount of the critical voltage reduction is strictly related to the amount of the
absorbed c-rays dose. Furthermore, at the failure voltage, the behavior of the device is affected by the
conduction of a current through the gate oxide. Moreover the SEGR of the device appears at lower voltages
due to the reduction of the Fowler–Nordheim limit in the c-irradiated devices
Single Event Effects in Power MOSFETs during Heavy Ion Irradiations Performed after Gamma Ray Degradation
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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