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power electronics technology
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SiC transistors can also operate at diodes. “On top of that, the solar
higher temperatures, cutting the industry is also extremely interested
cooling requirements for the power in SiC, whether it is high voltage
electronics in the inverter. diodes or switches.” He is also
seeing interest in SiC diodes for
Opportunities for savings are HEV, and in lighting applications.
greatest in the high-power, water-
cooled inverters used in solar farms, Infineon launched the world’s first
and far smaller in the air-cooled SiC diode to market in 2001, and it
versions used for small roof-top came out with a second-generation
installations. product in 2005. “The biggest
change from generation one to
A handful of SiC device makers have generation two was the added surge
CREDIT: Fraunhofer ISE
been developing various forms of explains to current capability, explains
SiC transistor over the last few Reynaerts.” This addressed the
years, and these products are thermal runaway issue that plagued would reduce capacitance and This summer
winning the attraction of solar the initial product - a cycle of rising improve high-frequency performance, Fraunhofer ISE
inverter manufacturers. For example, temperatures leading to an increase while simultaneously lowering raised the
ISET (Institut für Solare in resistance, a higher forward production costs. “What we did was efficiency of its
Energieversorgungstechnik, Kassel, voltage, and greater power find a way to get the heat out of the solar inverter to
Germany), has built a unit with a SiC dissipation that drove up the device’s package,” explains Reynaerts. 99.03 percent.
MOSFET that has an efficiency of temperature once more. Engineers developed a “diffusion The key behind
99.08 percent, according to Le soldering” process that almost its success was
Gouic. Early this year, Infineon launched a eliminates the solder layer between incorporation of
third generation of SiC diodes to the chip and the lead frame, and SiC JFETs
Developers of SiC transistors include address three issues: the customer’s produces a very good thermal made by
Infineon Technologies, which is desire for a less expensive product; connection for cooling. SemiSouth
working on a JFET that will better switching performance at Laboratories
complement its well-established higher frequencies; and improved The new approach gives third
range of SiC diodes. Interest in these efficiency when the inverter operates generation diodes about a 20
established products continues to at a relatively light load, such as 20 percent cost advantage over second-
grow, thanks to the emergence of percent of its maximum. “The third generation equivalents, if products
voluntary energy efficiency standards generation is an answer to all those are ordered in similar volumes.
for power supplies, according to Jan- points,” says Reynaerts. “We are not talking small beer,”
Willem Reynaerts, who combines the says Reynaerts. “This is really
role of Business Segment Manager Development focused on important for our customers. We are
for high-voltage metal-oxide improvements to device performance the leading supplier in power
semiconductors with worldwide at high current densities. This held semiconductors, and it is for us
responsibility for SiC Schottky the key to cutting chip sizes, which to lead in developing the SiC
market.”
These SiC products are still much
more expensive than their silicon
equivalents, but the gap is closing
fast, partly due to the reduction in the
cost of 4 inch substrates at higher
volumes. “There used to be a time
when SiC diodes were nearly an
order of magnitude more expensive,
but this is coming down to roughly a
factor of three, product for product,”
Infineon’s third generation of SiC Schottky barrier diodes have better says Reynaerts. Closing this gap is
thermal characteristics than their second generation equivalents. encouraging the SMPS and inverter
Improvement was driven by a switch from a solder-based join between manufacturers to think seriously
the chip and the package (left) to a diffusion solder attach (right). about SiC. “This message is starting
CREDIT: Infineon to sink in that at the system cost
September 2009 www.compoundsemiconductor.net 23
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