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Power devices and integrated circuits based on 4H-SiC lateral JFETs
No full textSilicon carbide (SiC) is a wide-bandgap semiconductor that has drawn significant research interest for the next-generation power electronics due to its superior electrical properties. Excellent device performance has been repeatedly demonstrated by SiC vertical power devices. However, for lateral power devices that offer the unique advantage of possible monolithic integration of a power electronics system-on-chip, the progress has been limited. This dissertation describes the 4H-SiC vertical-channel lateral JFET (VC-LJFET) technology that provides a suitable solution for power integration applications. Power devices based on this structure have a trenched-and-implanted vertical channel and a carefully designed lateral drift region, enabling normally-off operation with a high-voltage blocking capability. Low-voltage (LV) versions of VC-LJFET feature nearly identical device structures with a reduced drift length, and can be readily fabricated on the same wafer with the power devices. Essential components for a power integrated circuit, such as gate drive buffers, can be thus implemented monolithically on the VC-LJFET technology platform. This dissertation research starts with the process improvement investigation for the TI-JFET structure. Particularly, a novel ohmic contact scheme is developed using Ni to replace the troubling process in TI-VJFETs. The entire process flow of VC-LJFET is then designed and demonstrated in experiments, leading to the world’s first demonstration of a normally-off lateral power JFET in SiC. As of today, power JFETs fabricated in this technology are still representing the best-performing lateral power transistors in SiC and silicon. Based on the VC-LJFET structure, low-voltage circuits critical to the power integration applications are investigated. Gate drive buffer provides the interface between low-voltage control circuits and the power device, and is recognized as a key component for an integrated power electronics system. A thorough design, modeling and optimization work on the LJFET-based gate drive circuits is described. These buffer drivers using resistor or transistor loads will enable high-frequency switching of the power LJFETs at megahertz levels. The results achieved in this research strongly suggest the feasibility of SiC power integration technologies in general, as well as the suitability of the SiC VC-LJFET platform for such applications in particular.Ph.D.Includes abstractVitaIncludes bibliographical referencesby Ming S
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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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