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Continued improvement in silicon carbide (SiC) material processing has allowed development of efficient high temperature devices which are uniquely suited to power electronics circuit designs. The 4H-SiC structure has several intrinsic characteristics that facilitate optimal speed and power handling during high temperature device operation. These characteristics include wide bandgap (3.2 eV), high dielectric breakdown (3.5 MV/cm), and high thermal conductivity (4.9 W/cm-K)[1,2]. By combining these properties, SiC bipolar junction transistors (BJTs) can achieve fast, low impedance switching at high voltages (1.2 kV). New generation devices are being developed with increased current handling capability, as well as improved forward voltage characteristics. The device considered here, along with its on-state DC characteristic, is shown in figure 1. The BJTs are approximately 5mm by 5mm, and are nominally rated for a maximum Ice of 50A. Measurements on the Tektronix 371B curve-tracer indicate current gains over 60 at 25 oC and roughly 40 at 150 oC. These results were obtained at collector currents up to 20A. The base current for BJTs is typically 300 to 800 mA, depending on device temperature and the maximum device current required. In order to meet current handling requirements of up to 80A, as required for power conversion in modern military systems such as the hybrid-electric vehicle (HEV), it is necessary to configure these devices in parallel with minimal external cooling. The resulting switching circuits must therefore be validated for operation at high temperatures (package temperatures of 90 oC, and junction temperatures to 150 oC). Validation includes characterization of the devices in clamped inductive circuits with devices configured both alone and in parallel over time. Figure 4 shows measurement waveforms obtained during continuous clamped inductive switching. The primary focus of this work is to establish the overall performance and reliability of these newer generation SiC BJTs in power conversion circuits. Failure analysis and critical performance issues, such as current sharing, energy loss, and total reverse recovery charge are addressed. The initial results of the experiments indicate that these SiC switches have the potential to perform reliably in high temperature power conversion.

Significant development of silicon carbide (SiC) for device applications allows its uniquely favorable properties to be exploited in circuit designs. The 4H-SiC structure has several characteristics that provide optimal speed and power handling. These include wide bandgap (3 cV), high dielectric breakdown (3.5 MV/cm), and high thermal conductivity (5 W/cm-K) [1]. By combining these properties, SiC bipolar junction transistors can achieve fast switching at high voltages (1.2 kV). New generation devices are also being developed with increased current handling capability (above 10 A). However, in order to meet the power handling requirements of FCS systems, such as hybrid-electric vehicle (HEV) power conditioning, it is necessary to configure these devices in parallel and validate their operation at high temperatures (package temperatures of 90 degrees C, and junction temperatures to over 150 degrees C). This report documents experimental characterization of SiC BJTs fabricated by CREE in various applications, including parallel switching. The results presented here indicate that SiC is well suited to meet these goals.

The DIODE computer program at the Harry Diamond Laboratories (HDL) is used to compute current and voltage characteristics in semiconductors or gases. This user's manual serves two main purposes: (1) to document the present DIODE computer program in preparation for proposed improvements and (2) to allow others to use the program without personal instruction. Included are a brief history of the origin of the DIODE computer program, input data requirements, description of the computer code, output, and a discussion of the material parameters. Detailed instructions are included for the use of a remote IBM terminal on the Harry Diamond Laboratories site. Also included is a list of over 100 papers, reports, and oral presentations based on the DIODE program.

A few short years after the proclamation of liberalization, the government found itself faced with a burgeoning subsistence crisis and embroiled in a growing debate on the judiciousness of the reform. The reforms were meant to change the way in which the grain trade was conducted. The May Declaration radically altered the conditions of internal commerce and the July Edict opened the frontiers to exports. Taken together, these measures were supposed to build a stronger, more resilient and more dependable commercial structure at the same time that they generated powerful incentives for agricultural expansion. In this chapter we shall consider the impact of the reforms on domestic and foreign trade and especially on the customary patterns of provisioning. In addition, we shall examine the way in which partisans and adversaries of the May and July laws explained the relationship between liberalization and dearth.

The explosion of joy and gratitude which followed the promulgation of the liberal measures seemed to confirm the royal claims. The May Declaration elated the Journal Economique. In it the editors rediscovered the prince whose proud sobriquet had once been “the well-beloved”: they hailed “the august monarch that heaven gave for master to this great kingdom” and characterized him as “so justly cherished by all his people.” They regarded the Declaration as a genuine triumph but they esteemed it more for what it portended than for what it actually was likely to achieve. It was “a first step,” the “forerunner” of an “unlimited” freedom which the king would not deny the nation. La Chalotais, the Procurator General of the Rennes Parlement, asked the councelors to view the Declaration not “as a simple law of interior police but as a Blessing of the Monarch,” as one of those momentous acts which provide for “the happiness of peoples.” More than the measure in itself, it was the certainty that it “will undoubtedly be followed by a complete and general liberty to export” which enraptured the Breton magistrate.1