1,721,002 research outputs found
Going 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
High-Temperature Time-Dependent Gate Breakdown of p-GaN HEMTs
Full text linkIn this article, we present an in-depth high-temperature analysis of the long-term gate reliability in GaN-based power high-electron-mobility transistors (HEMTs) with p-type gate. Three different isolation process options, aimed at improving the time-dependent gate breakdown (TDGB), are proposed and compared by means of constant voltage stress tests performed at different forward gate biases, temperatures, and geometries. In particular, depending on the gate bias and temperature, the breakdown event may occur along the active gate area or through the isolation region. The results show different voltage dependency for such two different failure locations; therefore, two field-acceleration fitting models are needed for the estimation of lifetime. Furthermore, the gate time-to-failure (TTF) shows a non-monotonous temperature dependency at given gate bias. More specifically, a positive and a negative T-derivatives are observed at relatively low and high temperatures, respectively, which are related to active gate area and isolation region failure, respectively
Impact of structural and process variations on the time-dependent off-state breakdown of p-gan power hemts
Full text linkIn this article, we present an extensive investigation of the time-dependent drain breakdown occurring in GaN-on Si power HEMTs with p-GaN gate under long-term OFF-state stress. In particular, the time-dependent breakdown induced by high-temperature-reverse-bias stress is investigated as a func tion of different process and structural variations. Main results demonstrate that, by varying the gate-to-drain distance (LGD) and the field plates configuration, the physical location of failure changes as well. If LGD is relatively short (3 μm), the time dependent breakdown occurs through the GaN channel layer between drain and source. In this case, a thinner GaN layer significantly improves the device robustness to long-term OFF state stress. If LGD is relatively long (≥ 4 μm), the failure occurs between the two-dimensional electron gas (2DEG) and the source field plates. In this second case, the GaN layer thickness and LGD have no significant impact on the time-dependent breakdown, whereas the field plate lengths can be optimized to reduce the area exposed to high electric fields, hence limiting the probabil ity of failure. Finally, the role of the AlGaN barrier layer has been analyzed as well. If LGD = 3 μm, a thinner AlGaN layer is preferred, whereas if LGD ≥ 4 μm, a thicker layer with lower aluminum content gives rise to longer time to breakdown under OFF-State stress
Role of the AlGaN barrier on the long-term gate reliability of power HEMTs with p-GaN gate
Full text linkForward gate constant voltage stress (CVS) has been performed on GaN-on-Si (200 mm) HEMTs with p-GaN gate, controlled by a Schottky metal-retracted/p-GaN junction, processed by imec with different gate process splits. In particular, the adoption of devices with a different magnesium (Mg) concentration in the p-GaN layer, AlGaN barrier thickness and AlGaN aluminium percentage (Al%), allowed us to identify the degradation of the AlGaN barrier as responsible for time-dependent gate breakdown at room temperature. Lowering the Al% of the barrier and the Mg concentration of the p-GaN layer leads to a longer gate lifetime, while an optimum AlGaN barrier thickness is identified at given Al%
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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