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Performance
of 50 Completed ATP Projects
Status
Report - Number 2
NIST SP 950-2
Chapter
4 - Electronics, Computer Hardware & Communications
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Cree
Research, Inc.
Processes for Growing Large,
Single Silicon Carbide Crystals
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| Most
computer chips today consist of tiny electrical and electronic components
on a thin slice of silicon crystal. As many as five million discrete
components can be placed on a piece of crystal less than two inches
square. Silicon crystal chips, however, are quite sensitive to heat.
Electricity passing through a chip’s super-thin connecting wires
creates heat, just as it does in the heating element of a toaster.
If too much heat builds up, the chip loses its functionality. |
COMPOSITE
PERFORMANCE SCORE
(Based on a four star rating.)
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Cree's LED chips
are used by Siemens A.G. for back lighting for this dashboard. |
Beating the Heat in
Electronic Devices
This ATP project with Cree Research, a small company in North Carolina’s
Research Triangle Park, made significant progress in the development of
an alternative raw material for making crystal slices — silicon carbide.
This material belongs to a class of semiconductors having wide bandgap,
which means they are relatively insensitive to increased temperatures.
Silicon carbide’s thermal conductivity is greater than that of copper,
so it rapidly dissipates heat. It is impervious to most chemicals and
highly resistant to radiation. Silicon carbide is extremely hard —
it is used as grit in common sandpaper — indicating that devices
made with the substance can operate under extreme pressure. It also possesses
high field strength and high saturation drift velocity, characteristics
suggesting that devices made of it can be smaller and more efficient than
those made of silicon.
Cree and others have
shown that, even at red-hot temperatures, silicon carbide devices maintain
functionality. Some of them, in fact, have continued to operate at 650
degrees Celsius. The wide bandgap also allows silicon carbide devices
to operate at shorter wavelengths, enabling the creation of blue light-emitting
diodes (LEDs) that could not be made from silicon. Moreover, full-color
LED displays become possible with the existence of blue LEDs, as blue
was a missing primary color.
Growing Large Crystals
to Reduce Costs
Cree was founded in 1987 to commercialize silicon carbide and began by
making LEDs on a silicon carbide substrate. Prior to its ATP project,
Cree was already the world leader in silicon carbide technology and had
been making one-inch-diameter silicon carbide crystals. But progress in
the development of devices based on silicon carbide had been stymied by
difficulties in growing large, high-quality single crystals, a bottleneck
that led Cree to pursue more research.
The Real Color
DisplayT, a moving sign which is capable of displaying the full range
of colors, made possible by the use of blue LEDs. |
During the ATP project,
Cree advanced silicon carbide technology by developing methods to greatly
reduce the amount of imperfections in crystals and to increase their size
to two inches or greater in diameter. Larger diameter crystals result
in lower production costs, which are crucial to opening markets for silicon
carbide devices. The company also developed ways to significantly improve
the doping (adding impurities to achieve desired properties) and epitaxial
deposition (growing one crystal layer on another) processes for silicon
carbide. Improving doping uniformity directly increases production yield
and thus reduces costs.
Cree’s success
with the ATP project enables the fabrication of electronic devices that
can operate at much higher temperatures and withstand high power levels.
Silicon carbide components used in experimental high-definition television
(HDTV) transmission, for instance, delivered more power, lasted longer
and cost less to produce than conventional silicon-based components. Now
equipment that was costly to manufacture (owing to the need for heat-dissipation
systems) can be produced less expensively, and devices that were impractical
to make with pure silicon can be made with silicon carbide.
New Products: Blue
LEDs and Silicon Carbide Wafers
The ATP project has been highly productive for Cree and the economy at
large. The company has used the new technology to produce larger silicon
carbide wafers to use in its fabrication process for blue LEDs. It is
also offering the larger silicon carbide wafers for sale to other companies.
Cree is using the
ATP-funded technology to reduce the cost of producing blue LEDs, and their
sales have increased substantially. Production cost is primarily a function
of the number of wafers processed. If wafer size can be increased dramatically,
the cost per device will decrease dramatically because so many more devices
can be made on a wafer. The silicon carbide wafer technology is also aimed
at markets for other blue light-emitting optoelectronic devices, optical
disk storage, microwave communications, and blue and ultraviolet laser
diodes, as well as high-temperature, high-power, and high-frequency semiconductors.
The low-cost
blue light emitting diode (LED) produced with new silicon carbide
crystal technology. |
Benefits for the Economy
Benefits from the new silicon carbide technology are already accruing
to customers who have bought large volumes of blue LEDs or silicon carbide
wafers to use in their own production. Performance measures (resistance,
power output, sensitivity to light, operating temperature) for silicon
carbide devices are frequently large, relative to available alternatives.
Economic benefits from these performance improvements spill over to other
producers involved in fabrication and assembly before a wafer-based product
reaches the end user. The total of these incremental benefits is expected
to be much larger than the profits Cree receives for selling the silicon
carbide wafers.
Cree’s private
success has led to public benefit, which is expected to grow as the number
of applications for larger silicon carbide wafers increases. Westinghouse,
for example, used Cree’s silicon carbide wafers in fabricating components
for the transmitter it used in the first commercial-level HDTV broadcast
in the United States, in 1996. Westinghouse said its transmitter can deliver
three times more power, has longer life and costs less to produce than
conventional silicon-based transmitters. Although the number of HDTV transmitters
that will use silicon carbide wafers is unknown at this time, widespread
use of this technology in HDTV broadcasting could produce large general
economic benefits if it speeds commercialization of HDTV.
ATP Advantages
Cree reports it was attracted to the ATP as a funding source for the development
of the bulk crystal and epitaxial growth technologies because the company
could retain its process technology knowledge. The ATP award also helped
Cree form alliances with research partners and speed the development work,
enabling the company to get results about 18 months sooner than it would
otherwise have been able to do. During the course of its two-year ATP
project, Cree also grew significantly.
Company officials
say the success of the ATP-funded project was primarily responsible for
a subsequent award of $5.8 million from the Defense Advanced Research
Projects Agency (DARPA) to further develop silicon carbide growth processes
to produce three-inch wafers. If wafer size can be increased to three
inches, the cost per device will drop even further. This DARPA project
got under way in May 1995.
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Project
Highlights
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PROJECT:
To substantially reduce the cost and improve the durability of light-emitting
diodes (LEDs) and other electronic and optoelectronic devices by
increasing the quality and size (to 2 inches or more) of silicon
carbide (SiC) single crystals.
Duration: 6/15/1992 — 6/14/1994
ATP Number: 91-01-0256
FUNDING (in
thousands):
| ATP |
$1,957
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82%
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| Company |
435
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18%
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| Total |
$2,392
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ACCOMPLISHMENTS:
Cree essentially met or exceeded all of the technical milestones.
Successful development of the technology is indicated by the fact
that the company:
- applied for
one patent on technology related to the ATP project;
- presented
several papers at professional conferences;
- raised $13.2
million via an initial public stock offering in February 1993;
- made high-quality,
two-inch SiC wafers, greatly opening up the blue LED and SiC wafer
markets;
- raised approximately
$17.5 million in a private stock offering in September 1995;
- increased
annual revenues from $3 million at the start of the ATP project
in 1992 to $7.5 million at the end of the ATP award period in
1994;
- received
$5.8 million from the Defense Advanced Research Projects Agency
in May 1995 for further development of silicon carbide growth
processes to support production of three-inch wafers;
- formed Real
Color Displays, a wholly owned subsidiary, to exploit this technology
for full-color LED displays;
- received
a $6 million order in September 1996 from Siemens for blue LEDs;
and
- supplied
the SiC wafers for components in the SiC solid-state transmitter
used by Westinghouse Electric to make the first U.S. commercial-scale
high-definition TV (HDTV) broadcast in April 1996.
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COMMERCIALIZATION
STATUS:
The larger SiC wafers, made with the ATP-funded technology, are
being used in the fabrication of blue LEDs sold to many industrial
customers. The
wafers are also being provided in limited quantities for development
projects in government and industry research laboratories.
OUTLOOK:
The improved processing technology makes the outlook for the commercial
use of SiC crystals highly promising. The cost of producing blue
LEDs has already been reduced substantially, and the expected widespread
commercial availability of larger diameter SiC wafers promises a
new range of applications, including HDTV transmitters. Benefits
in the form of lower costs and higher quality will accrue to industrial
users of blue LEDs and SiC wafers, as well as to consumers who use
devices containing these two Cree products.
Composite
Performance Score:
COMPANY:
Cree Research, Inc.
2810 Meridian Parkway, Suite 176
Durham, NC 27713
Contact:
Calvin Carter
Phone: (919) 361-5709
Number of Employees: 41 at project start, 210 at the end
of 1997
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Return to Table
of Contents or go to next section.
Date created: April
2002
Last updated:
April 12, 2005
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