Peter Friedrichs

Planar aluminum-implanted 1400 V 4H silicon carbide p-n diodes with low on resistance

Planar p-n diodes with edge termination were fabricated by aluminum implantation on n-type 4H silicon carbide. These diodes exhibited an excellent blocking behavior up to 1400 V reverse voltage with stable avalanche breakdown at an electric field strength of 2.8 MV/cm. In addition, a nearly classical forward characteristic was observed with both recombination and diffusion current mechanism represented by ideality factors of 1.05 and 1.93, respectively. The turn-on voltage was 2.8 V. At a forward voltage drop of 6.2 V a current density of 4000u2009A/cm2 and a differential on resistance below 1u2009mΩu2009cm2 were achieved.

SiC power devices with low on-resistance for fast switching applications

Silicon carbide switching devices exhibit superior properties compared to silicon devices. Low specific on-resistance for high breakdown voltages is believed to be the most outstanding feature of SiC power switching devices. In this paper, MOSFETs and JFETs capable to block 1800 V with a specific on-resistance of 47 m/spl Omega/ cm/sup 2/ and 14.5 m/spl Omega/ cm/sup 2/, resp., are discussed. However, there are additional advantages making SiC devices attractive for the system designer. The authors present fast recovery of the 6H-SiC MOSFET reverse diode (Q/sub rr/ 30 nC, t/sub rr/ 20 ns) and fast switching as well as short circuit capability (1 ms) of vertical VJFETs. Finally, a short outlook to future SiC switching devices is given.

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.

Silicon carbide power semiconductors — new opportunities for high efficiency

After a hype and a consolidation phase regarding the potential of silicon carbide based components in power electronics (mostly diodes and switches), we are observing a solid penetration of these components in modern solutions even for power ratings of several kW. Benefits of these new power devices are now more clearly identified and applications were depicted where the use of these new components, in particular Schottky barrier diodes available from Infineon and Cree, can be a technical and commercial access. For a further market penetration, new generations of diodes as well as powerful switching devices are released recently resp. ready to commercialization. Especially upcoming markets for high voltage power devices offering not only high power densities, but energy saving as well push these developments. Supported by the improvements in base material quality and size, SiC power devices are believed to be on the hop to a next important step regarding its propagation in a broader range of applications. The paper will sketch these recent developments and will show how the improved performance can provide new perspectives in conventional systems as well as new solutions.

Stacked high voltage switch based on SiC VJFETs

Based on the serial connection of high voltage SiC VJFETs a stacked solution able to block very high voltages is presented. By connecting VJFETs in series, a unipolar high voltage switch with 8kV blocking voltage and an on-resistance of 2/spl Omega/ was fabricated. The basic functions of this stacked switch are analyzed by discussing the electrical behavior. The static and dynamic behavior indicates an interesting perspective for high voltage and high power applications. Especially the dynamics are carefully analyzed using a low voltage version of the stacked solution. Additionally, the potential of SiC VJFETs as a 4kV single switch is demonstrated.

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.

Charge Controlled Silicon Carbide Switching Devices

Charge controlled power switching devices fabricated in 4H-Silicon Carbide are discussed in this paper. After comparing possible structures, results on prototype devices are presented. The presentation will give an overview about the developments of SiC power switches at SiCED, in addition some potential applications serving as an accelerator for the SiC power switch development will be sketched. The performance of vertical JFETs will be analyzed in detail. These can be operated as a single device as well as in combination with a low voltage silicon power MOSFET. The result of the hybrid assembly is a normally off device which behaves for the user more and more like a classical MOSFET with respect to the input as well as the output characteristic. Several improvements where performed which make the device more attractive for the customer. It will be shown which factors drive these optimization and how they can be implemented. Although the primary target for this device is the >1000V blocking voltage range, it will be discussed how the huge 600V power switch market can be made accessible for SiC power devices too. Intensively the high temperature performance of SiC JFETs and Si/SiC cascodes is discussed. Additionally, other developments like silicon power MOSFETs or high voltage switches will be mentioned.

SiC Power Devices - Recent and Upcoming Developments

After a hype regarding the potential of silicon carbide based components in power electronics (mostly diodes and switches), we observed during the last years a consolidation phase. It was worked out that the expectation that silicon will be completely removed by SiC in power electronic applications will not happen in the timeframe foreseeable today. However, benefits of these new power devices were more clearly identified and applications were depicted where the use of these new components, in particular Schottky barrier diodes available from Infineon and Cree, can be a technical and commercial access already today. For a further market penetration, new generations of diodes as well as powerful switching devices are released recently resp. ready to commercialization. Especially upcoming markets for high voltage power devices like the hybrid car and the continuing trend to higher power densities push these developments. Supported by the improvements in base material quality and size, SiC power devices are believed to be on the hop to a next important step regarding its propagation in a broader range of applications. The paper sketches these recent developments and shows how the improved performance can provide new perspectives in conventional systems as well as new solutions

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.