SiC based devices

 

SiC SBDs are commercially available since 2001 ranging from the initial 300V/10A and 600V/6A to the more recent 600V/20A and 1.2 kV with current handling capabilities as high as 50A. Recently SiC SBDs with 1.7kV voltage rating have been announced. Due to the ease of paralleling, a wide range of power modules with almost every power handling capability used in applications could be addressed with SiC. Power modules containing SiC diodes with current capabilities of up to 600A are commercially available since 2006.  

Concerning SiC switches, 1200V SiC MOSFETs are commercially available since 2011 from Cree (USA) and Rohm (Japan). Normally-off SiC JFETs with vertical channel and no body diode have been commercially available (1200V/10-20A per chip) for some time, but the concept showed severe limitations and thus vanished quickly. In 2012, the 1200V CooSiC JFETs was released in the market by Infineon. It is a normally-off switch made of a with lateral channel JFET and body diode in cascade configuration with a low voltage Si P-MOSFET. In addition, SiC bipolar transistors with 1200V voltage rating and 12A and 40A current capability are commercially available and SiC thyristors with 6.5kV voltage rating and current ratings of 40- 80A have been announced. In conjunction with the recent material improvements, the development and fabrication of higher voltage SiC device concepts have been announced expanding the application field of SiC devices to high voltage systems. 

Since the beginning of the SiC device development, the applications aimed for were at voltage levels of several kV and high current levels. To address such applications with SiC devices, the blocking voltages and current ratings need to be continuously improved from the current commercial level to next generation of commercial devices. A key issue is material quality, but also unit device processes need to be improved to realize high performing devices.

High current capability SiC Diodes

As mentioned previously, SiC diodes are presently available from several suppliers and today 1.7kV diodes with 50A current ratings are available. However, to apply SiC devices in applications like traction or HV distribution, it is necessary to significantly increase the blocking voltage and the current ratings of the devices. In SPEED higher voltage range diodes will be developed for the targeted applications. 3.3kV, 6.5kV and 10kV class diodes of JBS and PIN type with current ratings of up to 30A per chip (depending on the voltage class) will be targeted, which is well above the current state of the art.

Highly reliable MOS gate dielectrics

Current gate dielectrics need further improvements including channel mobility, gate stability under large gate bias and reliability [28]. For low voltage MOSFETs (<1.7kV) the channel mobility has been an important performance limiting factor. However, for higher voltage MOSFETs the resistivity of the thick drift layer is dominating the on-state resistance. Hence, the main challenge in HV-MOSFETs is the reliability of the gate oxide layer. To address this challenge, this proposal considers different approaches using a Multi Systems CVD equipment incorporating MOCVD, Spray CVD, ALD and thermal annealing integrated in a single processing chamber. This allows the growth of reliable and novel stacks of dielectric layers on the semiconductor surface for gate and passivation purposes. 

Advanced SiC MOSFETs and other switch concepts

The 1700V SiC MOSFET + Diode concept to fulfil the requirements of wind power applications will be developed in the framework of this proposal. The currently available SiC MOSFET technology is not yet suitable for applying it to wind power systems and the performance of MOSFETs needs to be improved considerably in order to meet cost and performance ratios. In addition, current reliability levels are not acceptable for wind power applications and the use of an integrated body diode is judged as mandatory. Higher voltage range planar MOSFETs will be developed for the final applications. 3.3kV, 6.5kV and 10kV devices with current ratings of up to 25A per chip (depending on the voltage class) will be targeted, which is well above current state of the art. In addition, similar to Si technology, trench MOSFET devices have a great potential also in SiC. 

Currently, in terms of SiC switches, the closest competitor to the MOSFET is the SiC JFET. Therefore, the performance of SiC MOSFETs will be benchmarked against SiC trench JFET devices. We also aim at introducing innovative active area designs together with improved fabrication processes to reduce the cost of the SiC device technology (EURO/Amp); therefore, making it more competitive against Si-based solutions. 

Ultra HV SiC IGBT

A concept study of SiC IGBT will be performed. Different concepts will be simulated, including both P and N channel types, and the most promising will be fabricated and tested. This study will profit from Ascatron’s highly doped P++-epilayer and epitaxial re-growth technology.

The targeted breakdown voltage will be 10kV.