IEEE Power Electronics Magazine - June 2014 - 23
supplies. The company demonstrated a complete 250-W
ac-dc board that meets the requirements for an all-in-one
personal computer (PC) supply using three 600-V GaN-on-Si
Electric
Field
be a challenging task. By comparison, today's GaN HEMTs
utilize lateral conduction, wherein the die size increases with
the breakdown voltage. In addition, with lateral conduction,
heteroepitaxy makes high-voltage and high-current (greater
than 100 A) devices extremely difficult.
In conclusion, Heidel said that proving long-term reliability, applications engineering, and functional cost parity were critical remaining challenges for simultaneously
achieving high density, high efficiency, and high reliability
at a low cost for wide-bandgap devices.
G
LGD
D
S
GaN Reliability
i-Gan
Depletion Region
AlGaN
<111> Si Substrate
(a)
Depletion Region
G
Electric Field
S
p
n+
Junction
WD
n
n+
D
VDS(+ve)
(b)
fig 4 (a) GaN HEMTs today utilize lateral conduction. (b) ARPA-E
has funded the development of a vertical GaN transistor using
bulk GaN substrates. (Figure courtesy of ARPA-E.)
TDDB Model Projected Lifetime
99
99% Confidence Limit
1,100 V Test
1,150 V Test
50
Unreliability
Although there was a lot of talk about improving the reliability of GaN transistors under a variety of conditions, Transphorm revealed the results of such testing for its Joint Electron Device Engineering Council (JEDEC)-qualified 600-V
GaN-on-Si HEMTs in TO-220 packages under voltage stress.
According to Transphorm's paper "Moving Beyond Qualification to Verify the Long-Term Reliability of GaN Devices," presented by Yifeng Wu, Kurt Smith, and Carl Blake, the voltage
acceleration test predicted a 600-V lifetime of more than
107 h (Figure 5). However, for 480 V operation, under similar
voltage acceleration, the manufacturer boasts a lifetime
operation of 108 h, which translates to 100 million h. Other
extended tests show that failure under high-temperature
reverse bias for 8,000 h was +2% %50%, and high-temperature operating life using a hard switched boost converter
passed the 3,000 h at 175 °C test with no electrical degradation. Meanwhile, additional testing is in process to validate
the failure mechanisms. Blake, a consultant to Transphorm
and the president of C. Blake Kinetic Consulting, told the
attendees that the company was still studying the reliability
of 600-V GaN under thermal stress, which the supplier
intends to make available before the next APEC.
At the show, Transphorm also displayed its 600-V GaNon-Si HEMT in a low-profile Power Quad Flat No-lead
(PQFN) package, thus offering the JEDEC qualified 600
GaN-on-Si devices in TO-220 and PQFN packages. According to the maker, the new PQFN88 packaged parts feature
290-mX R DS (on), 29-nC Qrr, and low inductance for superior high-frequency switching capability. In addition, the
PQFN88-packaged "LD" devices offer a Kelvin connection to
better isolate the gate circuit from the high-current output
circuit to further reduce the electromagnetic interference.
In a statement, Primit Parikh, president of Transphorm said,
"Now by introducing the industry's first qualified 600-V GaN
PQFN-packaged products, we have increased the types of
applications where GaN can enable dramatically more efficient, compact, and low-cost solutions. This dispels the
widespread misconception that GaN isn't ready for primetime." He further added, "Once again, we've shown GaN
products are available today and are actually being used in a
multitude of real-world applications."
In terms of application, the company demonstrated
TO220-packaged 600-V GaN-on-Si HEMTs in lower-power
applications, such as adapters and all-in-one computer power
VDS(+ve)
Mean Failure Time Line
10
1
1E+ 06
IPL Model @ 600 V
1E+ 07
1E+ 08
1E+ 09
Time (h)
1E+ 10
1E+ 11
fig 5 The voltage accelerated tests for Transphorm's
600-V-rated GaN-on-Si HEMTs using the time dependent
dielectric breakdown (TDDB) model to predict an operation
lifetime of more than 107 h. (Figure courtesy of Transphorm.)
June 2014
z IEEE PowEr ElEctronIcs MagazInE
23
Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - June 2014
IEEE Power Electronics Magazine - June 2014 - Cover1
IEEE Power Electronics Magazine - June 2014 - Cover2
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