20-24 SiC v2 10/9/09 13:27 Page 24
technology power electronics
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“JFET behaves in many ways like a MOSFET would, with some differences in the drive.
It has a very familiar feel to circuit designers” Jeffrey Casady, SemiSouth Laboratories
level, in a lot of applications where SemiSouth’s normally-off JFETs have
energy efficiency is important, the recently been deployed in inverters
added cost of SiC over silicon is for photovoltaic systems that were
more than paid back.” built by Fraunhofer Institute for Solar
Energy Systems in Freiberg,
Infineon faces competition from a Germany. A conversion efficiency of
handful of other SiC diode 99.03 percent was announced this
manufacturers, including SemiSouth July, with the German team stating
Laboratories, which released its that the SiC JFETs were the key
product to the market in 2008. behind their latest efficiency
Jeffrey Casady, the company’s chief improvements. More recently, they
technical officer and vice-president of have shown that a SiC-based inverter
business development, says that its operating at 48 kHz with SiC
diode is similar to Infineon’s. products can outperform a silicon-
However, the company’s primary based equivalent running at 16 kHz.
focus is on the promotion of its JFET.
“We made the first normally-off JFET This means that it is possible for SiC-
in the summer of 2007, we started based inverters to not only deliver
ramping in 2008, and now in 2009 higher efficiencies than their silicon-
we have got reliability and based rivals, but also realize this When SemiSouth began its SiC The cells that
qualification data that looks really while using smaller, lower-cost transistor development, it could have generate
good,” says Casady. inductors and capacitors. decided to invest in a MOSFET, electricity are
JFET, or a bipolar device. “Every made of triple-
devices has its pros and cons,” junction III-V
says Casady, but SemiSouth devices grown
selected the JFET because of its on germanium
ruggedness, low cost, and avoidance substrates, and
of an oxide that can lead to reliability if DC-to-AC
issues. “It behaves in many ways inverters are
like a MOSFET would, with some gong to operate
differences in the drive. It has a at their highest
very familiar feel to circuit efficiencies,
designers.” then they need
to employ SiC
Casady says that the JFET is now diodes and
in low-volume production – transistors.
SemiSouth produces hundreds of CREDIT:
these wafers every month. SolFocus
Production is currently performed on
3-inch material, but the company
plans to convert to 4-inch in the next
year or two, when the higher volumes
justify this move.
By then the current blip in the solar
market will be in the the past, and
Semisouth, along with other SiC
transistor and diode makers, will be
battling it out for substantial
contracts with the builders of solar
inverters.
24
www.compoundsemiconductor.net September 2009
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