Characterization of a 4H-SiC High Power Density Controlled Current Limiter

International audienceMost of silicon devices such as Schottky diode, MOSFET, MESFET have been realized in SiC and show good electrical and thermal characteristics [1]. Considering fault current limiters for serial protection, a lot of structures exists [2, 3], from conventional fuses to other complex systems such as circuit breakers, mechanical switches. Up to now, few specific SiC-current limiter were described [4, 5]. This paper presents experimental characterization of a bi-directional current limiter structure based on a vertical SiC VJFET

The Allometry of Daily Energy Expenditure in Hummingbirds: An Energy Budget Approach

1. Within-clade allometric relationships represent standard laws of scaling between energy and size, and their outliers provide new avenues for physiological and ecological research. According to the metabolic-level boundaries hypothesis, metabolic rates as a function of mass are expected to scale closer to 0.67 when driven by surface-related processes (e.g. heat or water flux), while volume-related processes (e.g. activity) generate slopes closer to one. 2. In birds, daily energy expenditure (DEE) scales with body mass (M) in the relationship log (DEE)=2.35+0.68×log (M), consistent with surface-level processes driving the relationship. However, taxon-specific patterns differ from the scaling slope of all birds. 3. Hummingbirds have the highest mass-specific metabolic rates among all vertebrates. Previous studies on a few hummingbird species, without accounting for the phylogeny, estimated that the DEE–body mass relationship for hummingbirds was log (DEE)=1.72+1.21×log (M). In Contrast to the theoretical expectations, this slope \u3e1 indicates that larger hummingbirds are less metabolically efficient than smaller hummingbirds. 4. We collected DEE and mass data for 12 hummingbird species, which, combined with published data, represented 17 hummingbird species in eight of nine hummingbird clades over a sixfold size range of body size (2.7–17.5 g). 5. After accounting for phylogenetic relatedness, we found DEE scales with body mass as log(DEE)=2.04+0.95×log (M). This slope of 0.95 is lower than previously estimated for hummingbirds, but much higher than the slope for all birds (0.68). The high slopes of torpor, hovering and flight potentially explain the high interspecific DEE slope for hummingbirds compared to other endotherms

Characterization of a 4H-SiC High Power Density Controlled Current Limiter

International audienceCritical steps for the fabrication of SiC devices are thermal annealing and metal ohmic contact formation. Metal annealing effect on the electrical characteristics of the current limiter underlines the necessity to control this device fabrication step. Measurements of contact resistivity as a function of temperature demonstrate the stability of the N type Ni/SiC contact in the range of 175 K-450 K as its value remains constant around 40 µΩ.cm 2. Post implantation annealing effect on the sheet resistance (Rsh) shows that a 1700°C/30 min annealing gives better trade off in terms of dopant activation and surface roughness. High power density has been measured up to 600 V. Current thermal stability has been measured for an applied drain to source voltage of 100 V and exhibits high power density capabilities of SiC VJFET as a controlled current limiter. Introduction

Étude du comportement électrique du fusible aux fréquences élevées

Nowadays, the development of power semiconductors has made that fuses used for their protection have to be improved. The high working frequency of IGBT leads to a modification of fuse characteristics. For high frequencies, it may occur a bad working due to an unequal current distribution between two fuses in parallel, or even between fuse's elements. The result is that fuse operates at below rated current. This unexpected operation can be attributed to proximity effects which are consequences of electromagnetic laws between close conductors. To prevent such a failure, their current rating must be reduced as a function of frequency and distance between the fuselink and other conductors (e.g. the return conductor).L'évolution des interrupteurs semi-conducteurs de puissance est telle que les fusibles assurant leur protection ont dû eux aussi se développer. Ainsi, la fréquence de travail élevée de ces composants peut entraîner des modifications des caractéristiques du fusible. À haute fréquence, il peut apparaître un dysfonctionnement dû à une mauvaise répartition des courants entre des fusibles en parallèle ou même entre les différentes lames en parallèle constituant un fusible. Le résultat est alors une ouverture du fusible pour un courant inférieur à la valeur spécifiée par le constructeur. Ce dysfonctionnement peut être attribué aux phénomènes d'effets de proximité direct et inverse qui s'exercent sur plusieurs conducteurs proches. Pour éviter une ouverture intempestive, il est nécessaire de réduire le calibre du fusible en fonction de la fréquence et de la proximité d'autres conducteurs (par exemple le conducteur de retour)

Compatibility of VJFET Technology with MESFET Fabrication and Its Interest for System Integration: Fabrication of 6H and 4H-SiC 110 V Lateral MESFET

International audienceIntegration of Power devices with their control circuitry is a usual challenge in Si and SiC technologies to increase efficiency of power switch and systems. The purpose of this article is to evaluate the integration compatibility of lateral MESFETs within a Vertical power JFET fabrication technology. The interest of this method is to allow control circuitry based on MESFET devices to get both power devices and control circuits on the same die. Several possibilities can be foreseen for the realization of lateral SiC-MESFETs [1], using conductive substrates or semi-insulating wafers. Other possibilities, more compatible with a vertical power device process, are P and N well formation by ion implantation to form the lateral channel. The description of the fabrication process presented below is a part of the fabrication process of a VJFET designed for high voltage current limitation [2]. High energy implantation, RIE etching adjustment and metal contact annealing are the critical steps of the fabrication of this device and will be developed in the process description. Electrical characterization of fabricated MESFET exhibit specific on resistance of 38mΩ.cm² and a transconductance value of 0,4 mS.mm-1. These results demonstrate VJFET and MESFET fabrication technology compatibility. Keys points to improve for the next generation of devices will be presented as well