Benno Weis

Dynamic characteristics of high voltage 4H-SiC vertical JFETs

We have developed a novel structure for a fully implanted, normally-on vertical junction field effect transistor (VJFET) and fabricated prototypes with blocking voltages between 600 and 1000 V. Mounting the SiC VJFET together with a 50 V Si MOSFET on a DCB substrate in a cascode circuit, we obtain a normally-off high voltage switch. The specific on-resistance of the VJFET was sufficiently low, in the range of 18 to 40 m/spl Omega/cm/sup 2/, for various blocking voltages. The dynamic behaviour shows turn-off times between 50 ns and 2 /spl mu/s due to the RC-product of two different p-gate networks.

Switching behaviour of fast high voltage SiC pn-diodes

4H-SiC p-n diodes with an active area of 1 mm/sup 2/ and up to 3 kV blocking voltage have been fabricated, characterized and compared to simulations. The static forward characteristics demonstrate the expected forward power loss with a negative temperature coefficient. The diodes exhibit a stable avalanche breakdown, showing a small positive temperature coefficient (0.3 V/K). The turn-on switching behaviour shows a relatively small voltage overshoot as compared to silicon diodes. The turn-off resembles that of a Schottky diode. In both cases, the dynamics can be attributed to a rapid recombination of the storage charge, even under high forward injection conditions. Numerical simulations may point to a local lifetime reduction at the p-n junction.

Electrical performance of triple implanted vertical silicon carbide MOSFETs with low on-resistance

This paper describes results of 6H silicon carbide vertical power MOSFETs designed for different blocking capabilities: 600 V and 1600 V. The fabrication is based on a triple implantation technique with a lateral inversion channel. The MOSFETs are normally off and exhibit specific on-resistances of 22 and 40 m/spl Omega/cm/sup 2/, respectively. A chip area of 1 mm/sup 2/ has emerged as a suitable value in order to achieve an acceptable yield with respect to the blocking capability. A SiC MOSFET of this size can be driven up to 1 A in continuous operation. As expected for a unipolar device, short turn-on and turn-off delay times have been measured. In particular, due to a very small accumulation zone, the Miller capacitance is small in comparison to Si MOSFETs. The switching speed can be influenced by the gate driving circuit in a wide range. The SiC MOSFET is controllable in all switching states and stable up to 125/spl deg/C case temperature. The switching behaviour tested under conditions typical for motor drives is robust against short cuts and short time overloading.

Characterization of fast 4.5 kV SiC p-n diodes

New results of silicon carbide p-n diodes show a promising performance for high voltage applications. The diodes are characterized by high power ratings, temperature stability, rugged avalanche and fast switching behavior. Significant savings in system cooling equipment seem possible. However, with todays available material the device areas and thereby current ratings which can be fabricated with reasonable yield are restricted to a few square mm resp. a few amps. The SiC p-n diodes are fabricated with implanted p-regions on 39 /spl mu/m thick n-type epitaxial layers with a doping concentration of 2/spl times/10/sup 15/ cm/sup -3/. They exhibit a stable avalanche breakdown at 4800 V and a low leakage current (<20 /spl mu/A/cm/sup 2/) prior to breakdown. The on-state is characterized by a voltage drop of 4.0 V at a current density of 100 A/cm/sup 2/, corresponding to 2.2 A. For current densities above 80 A/cm/sup 2/ lower static losses have been achieved compared to equivalent silicon high voltage diodes. The temperature coefficient is slightly positive guaranteeing a homogeneous current sharing for operation in parallel. The switching performance is characterized by very low dynamic losses. The reverse recovery current peak is considerably lower than the forward current, with a reverse recovery time as short as 30 ns.

Concepts for a DC network in industrial production

In this paper, concepts for an extended DC network for the main power supply of components from various manufacturers in industrial production are presented. In the first part, detailed requirements for such a network are given from the viewpoint of a customer. Based on those, different concepts for AC/DC conversion and energy management are discussed. As far as AC/DC conversion is concerned, the advantages and drawbacks of several rectifier topologies are listed, as they have a significant impact on the system behavior and EMC properties. An intelligent energy management can improve the energy efficiency and reduce downtimes of a plant, which are major requirements from a customers viewpoint.