323,041 research outputs found
Gate stability of GaN-Based HEMTs with P-Type Gate
No full textThis paper reports on an extensive investigation of the gate stability of GaN-based High Electron Mobility Transistors with p-type gate submitted to forward gate stress. Based on combined electrical and electroluminescence measurements, we demonstrate the following results: (i) the catastrophic breakdown voltage of the gate diode is higher than 11 V at room temperature; (ii) in a step-stress experiment, the devices show a stable behavior up to VGS= 10 V, and a catastrophic failure happened for higher voltages; (iii) failure consists in the creation of shunt paths under the gate, of which the position can be identified by electroluminescence (EL) measurements; (iv) the EL spectra emitted by the devices consists of a broad emission band, centered around 500–550 nm, related to the yellow-luminescence of GaN; and (v) when submitted to a constant voltage stress tests, the p-GaN gate can show a time-dependent failure, and the time to failure follows a Weibull distribution.Meneghini, M.; Rossetto, I.; Rizzato, V.; Stoffels, S.; Van Hove, M.; Posthuma, N.; Wu, T.-L.; Marcon, D.; Decoutere, S.; Meneghesso, G.; Zanoni, E. Gate Stability of GaN-Based HEMTs with P-Type Gate. Electronics 2016, 5, 14
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Threshold Voltage Instability in GaN HEMTs with p-Type Gate: Mg Doping Compensation
No full textIn this letter, we present an analysis of the threshold voltage shift induced by positive bias temperature instability stress in GaN-based power HEMTs with p-type gate, controlled by a Schottky metal/p-GaN junction. In particular, we show the positive effect of the magnesium compensation process in the p-GaN layer on the long-term threshold voltage instability. When a relatively high positive bias is applied to the gate (Schottky junction reversebiased), holes are generated by impact ionization in the high-field depleted p-GaN region, then accelerated toward the AlGaN layer. The high-energy holes, combined with the high temperature effects, create defects in the AlGaN or at its interface with p-GaN, causing a long-term positive threshold voltage shift. A process variation in the p-GaN layer is introducedwhich promotes a wider depletion region near the Schottky interface with the metal, lowering the electric field and reducing the generation of holes due to impact ionization. As a result, the long-term threshold voltage instability is improved without altering the dc transistor parameters, such as threshold voltage, trans-conductance, and subthreshold slope
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Using RESURF Technique for Edge Termination of Semi-Vertical GaN Devices
No full textThe Reduced Surface Field (RESURF) technique has been adopted to GaN based edge termination structures and is illustrated using Technology Computer Aided Design (TCAD) on a semi-vertical pn junction diode. It is shown that with the introduction of an additional p-type RESURF layer, the breakdown voltage can be enhanced as in the classical RESURF technique. These edge termination structures can reach breakdown voltages close to the theoretical, parallel-plane breakdown voltage thereby avoiding lower corner breakdown voltages in standard structures without a RESURF layer
Gate Reliability of p-GaN HEMT with Gate Metal Retraction
No full textIn this paper, we present an analysis of the gate degradation induced by long-term forward gate stress in GaN-based power HEMTs with p-type gate, controlled by a Schottky metal-retracted/p-GaN junction. In particular, time-dependent gate breakdown and threshold voltage instability are investigated as function of different geometries, gate biases, and temperatures. The introduction of a gate metal retraction (GMR) process step improves the device lifetime because it suppresses the onset of the leakage current flow occurring at the gate edges for relatively high gate voltage. However, biasing GMR p-GaN HEMT at VG > 8 V and T > 80 °C, a new degradation mechanism shows up, possibly altering the lifetime even at low VG operation. Main results in this paper demonstrate that, although at high-VG and high-T a localized degradation effect ascribed to the device isolation region is responsible for time-dependent gate breakdown, thanks to GMR higher operating voltages compatible with 10-years continuous operation is attained. Finally, the longer device lifetime at moderate VG values brought by GMR, allows to evaluate the threshold voltage instability for long stress times (≈ 112 hours) at relatively high-VG and high-T, leading to the observation of a saturation of the long-term positive threshold voltage shift, and providing additional information about the underlying physical degradation mechanisms. Overall, the saturated 0.65 V ΔVTH under worst-case condition (VG = 7 V at 150 °C, i.e. corresponding to 10 years lifetime), reveals a reliable and fairly stable technology with respect to forward gate stress
Trapping mechanisms in GaN-based MIS-HEMTs grown on silicon substrate
No full textIn this work we report on the three dominant trapping mechanisms affecting the dynamic performance of a double-heterostructure GaN-based MIS-HEMT grown on silicon substrate. In the OFF-state, with high drain voltage and pinched-off 2DEG, the dominant mechanism is the charge-trapping in the gate-drain access region caused by the transversal drain-to-substrate potential. This effect causes the dynamic increase of the ON-resistance, and is positively temperature-dependent, thus of great concern for high-temperature operation. In the SEMI-ON-state, due to the presence of high VDS and relatively high IDS, an additional trapping mechanism emerges, involving the injection of hot electrons from the 2DEG into trap states located in the GaN-buffer or in the AlGaN barrier. This mechanism, critical in hard-switching operations, affects both the ON-resistance and the VTH. Finally, when the gate is positively biased (gate overdrive state) trapping of electrons happens in the gate dielectric layer(s), leading to strong metastable VTH instabilities. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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