SiC continues its rise towards more efficient applications
Kista Science Tower, Stockholm, Sweden May 29-30, 2012
For the 4th edition of the International Silicon Carbide Power Electronic Application Workshop (ISiCPEAW) in Stockholm, the SiC manufacturers and users community met to discuss recent progress in components, power modules and their system implementations. And while new devices are released and new actors are entering the market, the competition between both manufacturers and device technologies become tougher. However, GaN, the other wide band gap technology with great potential in power electronics, has soon to be considered as another challenger.
In this late but rather warm Swedish spring, the world SiC community met at ISiCPEAW 2012 and highlighted this more than ever dynamic field as well as the rising market of SiC devices.
New Devices, New Players
Paul Kierstad from CREE presented the recently released products in the 1700V range: a 40mohm MOSFET and a 50A Schottky diode. Both products were used as part of a 40kW demonstrator developed together with APE Inc. allowing an efficiency higher than 98.5%. One important feature of the MOSFET compared to other switches is its ruggedness, especially when it comes to avalanche. CREE demonstrated a 1.5J repetitive avalanche on their MOSFET, a value 10 to 100 times higher than Si MOSFET. Another important feature of MOSFETs was confirmed by Mineo Miura from Rhom: the Rdson is less temperature dependant than in other switches. Rhom will commercially release two SiC devices this year, a Schottky Barrier Diode and a MOSFET. Both have been used in a 120A SiC module in which 5 switches are placed in parallel.
Uwe Jansen, Infineon, announced the 5th generation of SiC Schottky diodes with improved performance (lower voltage forward x charge product) for a lower cost than the 2nd generation, before presenting the commercial release of a 1200V 100mohm SiC JFET. To simplify the use of this normally ON device, Infineon developed a dedicated IC driver enabling normally off operation thanks to a low-voltage silicon PMOS transistor placed in series with the JFET ensuring safe off state at turn-on. During normal operation, the bottom PMOS is not switched and is kept in on-state. The JFET is directly controlled by the driver IC, allowing a more efficient and a better gate driving (JFET gates have lower capacitance than MOSFET) compared to the cascode approach. The Infineon JFET is also equipped with an internal body diode.
Mietek Bakowski from Acreo in Sweden presented a buried grid SiC JBS diode. This concept has successfully been implemented in SiC thanks to epitaxial techniques allowing the construction of a doped buried grid. The result is a diode with improved trade-off between the on-state and reverse characteristics having extremely low leakage current in blocking state.
Bipolar Power Modules
Lead frame of the transfer molded module, including 12 SiC BJT and 12 SiC Schottky diodes
Fairchild presented developments in the field of SiC Bipolar transistor and shall release soon a 1200V-15A (57mohm) and a 1200V-50A (19mohm) switches. Two packages will be available: a plastic TO247 for high efficiency operation and a TO-258 for high temperature operations. Fairchild achieved a gain of 100 @25ºC and 60@ 150ºC, which can be considered as an important achievement knowing that the gain drop with temperature rise is a known drawback of bipolar technology. A simulation model has also been developed for LTspice and a dedicated base driver is in development to accelerate integration into future products.
Another major development occurred thanks to collaboration between Fairchild, the Kiel University and Danfoss to create a 1200V 300A power module based on SiC BJT from Fairchild and SiC diodes from CREE. In this project the 24 dies (12 transistors and 12 diodes) were sintered in a transfer molded module in place of a framed module. The advantages are a more compact design and less wire-bonding, leading to lower parasitics and, hence, higher efficiency. The sintering offers a greater reliability towards temperature cycling and higher operational temperature. During the design of the module, a great care has been given to the leadframe dimensions in order to handle the large currents (Section >4mm2). The mechanical dimensions were selected to respect air gap and creeping distances (pin to pin and pin to cooler). For the mechanical assembly, a mounting bracket is used to press the module onto a water cooling device. The final result is a very low 0.8K/W die to water thermal resistance.
NOR gate based on SiC bipolar ECL technology
SiC is often presented as an ideal material not only due to its electrical superiority but also due to very high temperature operation. In order to make use of this property, Liam Mills form Semelab in UK showed a new module design based on Silicon Nitride substrate offering a direct interfacing (no base plate), a hermetic package and multilayer possibilities, hence reducing inductance. Lam Mills presented excellent results regarding the manufacturing default, temperature cycling and thermal resistance.
So packaging techniques are progressing towards higher operation temperature, but there is still a difference between the temperature SiC can handle and what traditional driving electronics can withstand.
Cissoid from Belgium is filling this gap by presenting their high temperature half-bridge isolated gate driver reference design HADES, opening new doors to high temperature operations. HADES can be placed as close as possible to the power devices and can drive last generation of wide band gap enhancement unipolar semiconductor devices (bipolar or N-ON JFETs on request) and traditional Si MOSFETs and IGBTs. The HADES design is compatible with 1200V supply, and can operate at more than 200kHz. The demonstration board is made of polyimide and all components, transformer included, can operate up to 225ºC (175ºC ambient).
But beyond these Si components tailored for high temperature operation (250ºC max), more radical approaches are exploited at the Royal Institute of Technology in Stockholm in order to produce ICs able to withstand more than 400ºC operation as well as high levels of ionizing radiation. Professor Carl Michael Zetterling from KTH presented recent works and developments in integrated circuits based on SiC material. Many aspect of the IC development have been investigated such as transistor characterization, radiation hardness, bandgap reference voltage, high temperature metallization leading to the design and the construction of ECL OR and NOR gates made in SiC bipolar technology.
Several applications of SiC components were shown during ISiCPEAW 2012. Carl N.M. Ho from ABB Switzerland presented an industrial application of SiC devices in a PV inverter. The replacement of the Si diodes by SiC Schottky diodes in the pre-regulator of 2.5kW photovoltaic inverter helped to improve efficiency (+1%), meaning less thermal dissipation and hence a smaller cooling system, this having an impact on the pre-regulator size (47% percent reduction) and its cost. The benefits for the user are clear: a more compact and more efficient equipment. But when it comes to the inverter itself, the benefits can be even higher: the high breakdown voltages of the SiC switches as well as their high operating frequency allow a simplification of the inverter topology and even removing components.
Shashank Krishnamurthy from the research center of United Technologies, USA, showed a high frequency SiC based 5.5kW inverter for aerospace applications. The demonstrator made use of SiC MOSFETs and SiC Schottky diodes with a PWM frequency of 400 kHz, thus allowing a very compact transformer and lighter passive filters.
SiC vs. GaN
This edition of ISiCPEAW is also innovative for a special session dedicated to its main competitor: for the first time, several representatives of the GaN business were invited to present the latest developments.
Under contract for the DLR (German National Space Adminstration) and the European Space Agency, the Ferdinand Braun Institut of Germany, represented by Joachim Wuerfl, developed an 85mohm 200V 50A max with a Vth =1.2V and a 75mohm 250V 75A max in under-bump package. They also designed and manufactured a 1000V Schottky diode using GaN epitaxy on Si and SiC substrate, the second one offering better performances in terms of blocking voltage but also a higher cost.
Nobuyuki Otsuka from Panasonic in Japan presented several devices all made of GaN epitaxy on 6 Si wafers. The epitaxi is deposited in multilayer alternating GaN and AlN in super lattice, in order to reduce stress and possible cracks. The main development is called GIT for Gate injection Transistor allowing normally-off operation and low on-resistance. Among the devices developed with this technique, there is a monolithic 3 phase inverter and a bidirectional switch for AC supplies equipped with 2 gates. Panasonic also showed a 9.4kV diode. A monolithic inverter (6 transistors on a single die) is possible only with lateral devices such as the ones obtained with GaN processes while most devices made in SiC are vertical devices. One big advantage of the monolithic inverter is its very high integration and very low parasitic inductances.
Paul Kierstad (CREE), Uwe Jansen (Infineon) Joachim Wuerfl (Braun Institute) and Philippe Roussel (Yole Développement) during a SiC GaN round table.
But in spite of constant development and important investment in the GaN domain, the GaN market is still lagging behind the SiC one. Philippe Roussel from Yole Développement in France presented GaN and SiC Market projections. According to these estimations, the GaN should catch up in the two coming years, but only if the GaN on Si really takes-off. While the supremacy of SiC for application over 1kV is not questioned, GaN and SiC devices might be in tough competition for the 600V and 900V market segment: CREE will not let go the 900V market said Paul Kierstad, which also pointed out that the cost per device for SiC has dropped dramatically since first market introduction. Philippe Roussel presented some new entrant in the SiC business, mainly in China. Another important point of the discussion was the introduction of the 6 SiC wafer: CREE has announced a soon release of 150mm wafer even though there are some uncertainties on the demand: the 150mm will reduce costs and enlarge dramatically the number of devices produced, but is there a market yet for such a high number of components? Market projections might bring an answer to this question since the power device market is growing at 8% per year, with a global market prevision of 35B$ in 2020. This represents a strong opportunity for the SiC industry.
Tuesday May 29
REGISTRATION + COFFEE
Hans Hentzell, CEO Swedish ICT, Chairman Acreo
KEYNOTE SPEAKERComparison of SiC devices
Per Ranstad, Alstom
Highly reliable SiC MOSFETs and power modules
Mineo Miura, ROHM
SiC - for Diodes, JFETs and Modules
Uwe Jansen, Infineon
B2B booking Update your personal meeting schedule
Cree SiC MOSFET Advances
Paul Kierstead, Cree
1200 V SiC bipolar junction transistors with fast switching and low VCESAT
Martin Domeij, Fairchild
LUNCH + EXHIBITION
HADES, the First Gate Driver Chipset dedicated to Extended Lifetime & High Power Density Converters
Pierre Delatte, Cissoid
Novel Gate Driver for Normally-off SiC JFET and General High Temperature SiC Converter Technology
Benjamin Wrzecionko, ETH
Parallel connection of SiC JFETs
Dimosthenis Peftitsis, KTH
High Frequency Inverter Design Using SiC Devices
Shashank Krishnamurthy, UTRC
SiC JFET Switching Behavior under Influence of Circuit Parasitics
J.A. Ferreira, TU Delft
SiC market and industry status: How to find its way between Silicon and GaN
Philippe Roussele, Yole
SiC Power Center
Per Ericsson, Acreo
MINGLE, BAR, BAND
DINNER + ACTIVITY
Wednesday May 30
SiC packaging, planned activities at Swerea KIMAB
Tag Hammam, Swerea KIMAB
Packaging Semiconductors for High Temperature Environments
Liam Mills, Semelab UK
Innovative SiC-Traction Module manufactured in Sinter- and Transfer-Mould-Technology
Ronald Eisele, Uni. Kiel
High Current High Performance All Silicon Carbide Power Modules
Marcelo Schupbach, APEI
SiC challenges in heavy vehicles
Mats Alaküla, Volvo AB
PANEL DISCUSSION How SiC can find its way between incumbent Silicon and emerging GaN technologies
LUNCH + EXHIBITION
Contribution of SiC in 3-phase PV Inverters
Carl Ho, ABB
AC vs DC - second round
Anders Mannikoff, SP
Highly Integrated 5kW On-board Charger for Plug-in HEVs Using SiC Devices
Marcelo Schupbach, APEI
Merits of buried grid technology for SiC JBS diodes
Mietek Bakowski, Acreo
GaN high voltage power transistors for switching applications
Hans-Joachim Wurfl, Ferdinand Braun Inst.
GaN Power Electron Devices
Otsuka Nobuyoki, Panasonic
HIGH TEMP ELECTRONICS
KTH Integrated Devices and Circuits in SiC for Harsh Environment Applications
Carl-Mikael Zetterling, KTH