technology conference report
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IEDM showcases the strengths
of III-V transistors
Highlights from IEDM 2009 include the development of novel, normally-off GaN
transistors for power electronics and improved gate dielectrics for III-V transistors
targeting logic applications. Richard Stevenson reports.
T
he 2009 International Electronic Devices Meeting The inverter features six of the company’s gate injection
(IEDM) had a similar flavour to its recent transistors (GITs) integrated onto a single chip. These
predecessors: developments in silicon CMOS transistors are normally-off, which means that they are
technologies dominated the agenda, but there was also a inherently safer and use a more robust mode of operation
smaller number of papers detailing important that the more common normally-on transistor. The GIT
breakthroughs in III-V devices. Several of these focused also has a very low switching loss, enabling the
on GaN-based devices for high-power electronics, and a construction of an inverter with a conversion loss that is
handful described breakthroughs relating to successors to 42 percent less than that of the incumbent technology - a
silicon transistors for logic applications. silicon-based insulated gate bipolar transistor.
Panasonic, NEC and HRL Laboratories all reported The epistructure for Panasonic’s inverter is grown by
advances in normally-off transistors that can be used to MOCVD on silicon substrates, and normally-off operation
The 2009 perform functions such as switching a DC signal to an AC is realized through a p-type AlGaN gate above the
International form, or boosting output voltages. Both of these types of AlGaN/GaN heterostructure. The authors from Panasonic
Electron manipulations are needed in circuits built for motor drives claim that the transistor delivers an extremely high drain
Devices and for the linking solar panels to the grid. current and a low on-state resistance, thanks to
Meeting was conductivity modulation resulting from hole injection from
held between Researchers from Panasonic claimed to have made the the p-type gate. Every transistor in the chip has to be fully
7-9 December first single chip, GaN-based inverter IC for motor drives. isolated from the other five. This is realized with an iron
in Baltimore, Their device, which converts a DC source into an AC ion doping process that is even remains stable at
MD. form, has led to the filing of 141 domestic and 90 temperatures well above 1000 degrees C.
Credit: IEEE overseas patent applications.
Device testing reveals a typical off-state breakdown
voltage for the GITs of 700 V, thanks to the thick GaN
buffer layer. The threshold voltage and off-state leakage
current are stable for over 1000 hours, according to bias-
temperature reliability studies.
The engineers at Panasonic have used these transistors
to form inverter ICs. Fast recovery diodes are not used in
these circuits. Although they have a recovery time of just
50 ns, they are inferior to Panasonic’s GITs that recover
in just 20 ns.
The 2.5 mm by 2.7 mm inverter built from these
transistors employs GITs with a 25 nm gate width. This
monolithic chip can deliver an operating efficiency of 93
percent, even at low output conditions of 20W out of a
100W motor driving system, and the researchers claim
that even higher efficiencies are possible by cutting the
on-resistance in a larger chip.
38
www.compoundsemiconductor.net January/February 2010
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