Sand is one of the most abundant materials on the planet,
which is one reason for the central role it has captured in modern microelectronics.
Compounds of silicon and oxygen, typically in the form of sand, account for
about three-fourths of the earth's crust. In a highly refined form, they also
are the materials of choice for the electronics industry because of their excellent
A semiconductor is a substance about halfway between a
conductor (like metal, which passes electrical current along readily) and an insulator
(such as rubber, which stops the electron flow). When overlaid with the right
impurities, silicon chips become semiconductors, carrying current along
designated paths and through selected gates under certain conditions.
This makes them good switches, which is essential. All data
in modern information processing systems are represented in digital form, either
as a "one" when the devices are conducting or as a "zero"
In addition to its universal availability, silicon has the
advantage of high electron mobility. That's why silicon is so good for
switches; the faster the electrons can move through it, the faster the
computers made of silicon devices can operate.
Silicon is a member of the carbon family, found in column
four of the periodic table. Carbon, the basic building block of all life and an
electronics material, forms more compounds than all the other elements on the
table combined. The other members of this family are germanium—used to make
the first transistor in 1947 and today a key ingredient of optical fibers—tin,
and lead, which are basic to future applications of superconductivity and
advanced sensor systems.
Physical chemists have long known that still higher rates of
electron mobility are inherent in compounds formed out of elements from
columns three and five of the periodic table. In theory, these 3-5 compounds,
as they're known, should replace silicon in future high-performance
information-processing systems. They haven't yet because they're hard to work
with, and the materials-processing technologies haven't kept pace with silicon.
Until now. Starting in 1986 with the Microwave/Millimeter
Wave Monolithic Integrated Circuits (MIMIC) program at the Defense Advanced
Research Projects Agency (DARPA), 3-5 technology has advanced to the point
where it's beginning to close the gap with silicon.
MIMIC was aimed at analog applications in weapon sensor systems
such as radar. Instead of processing the data as ones and zeros, the MIMIC
devices generated representations, or analogs, of the targets of interest in
the form of voltages that were then converted to a digital format and
processed by onboard digital computers. The idea was to quickly accumulate and
pass on to the computers large volumes of intelligence data for identification
and appropriate response.
First of the 3-5s
MIMIC also pushed the technology of the first of the 3-5
compounds, gallium arsenide (GaAs). With an electron mobility about five times
that of silicon, plus reduced power requirements and inherent resistance to
radiation, GaAs was the perfect material to break the front- end bottleneck of
airborne systems. GaAs devices derived from MIMIC, such as the
transmit/receive modules for the Westinghouse phased-array radar on the Air
Force's Advanced Tactical Fighter (ATF), have begun finding their way into
Now, building on that base, the solid-state physics
community is accelerating its efforts along two paths: using these new
materials in the more demanding digital applications and experimenting with
other 3-5 compounds that have even greater potential performance than GaAs.
Once again DARPA is leading the military effort, this time
with a program to insert digital GaAs technology into eleven current weapon
systems as one-to-one replacements for existing silicon devices (see box). The
major advances, however, are coming from the commercial world. Even before the
DARPA program began, Seymour Cray, the legendary progenitor of supercomputers,
began designing his next machine entirely out of digital GaAs logic. Known as
the Cray 3 and expected to be the world's most powerful supercomputer, the new
machine is scheduled for initial deliveries in mid-1991.
Meanwhile, the basic research organizations of Bell
Laboratories (which demonstrated that first germanium transistor), Hughes,
IBM, and others are reporting initial successes with such other 3-5 combinations
as indium phosphide (InP), aluminum indium arsenide (AlInAs), and gallium
indium arsenide (GaInAs). In each case, the key to improved performance lies in
increasing the content of indium, because it has the potential of improving
electron mobility three or four times beyond GaAs.
Memory is the Bellwether
GaAs thus represents the opening wedge of a revolution that
is transforming electronics. Today, the technology is about where silicon was
in the early 1970s, when Silicon Valley in California was turning out sample
quantities of the first crude microprocessors and semiconductor memories.
Those devices have since become ubiquitous, making possible the present era of
distributed computing and intelligent weapons. A bellwether is memory, which
has gone from a thousand bits per chip to a million, at essentially the same
Price-performance achievements like that are a function of
volume production. That's what the DARPA program is all about, according to
Dr. Arati Prabhakar, GaAs program manager in the agency's Defense Sciences
Office: building the necessary infrastructure. That's also why DARPA chose
weapon systems currently in production. "We're taking one risk at a
time," she adds.
Two of the Army demonstration projects, in particular,
should drive up digital GaAs volume, according to Sven A. Roosild, DARPA assistant
director for electronic sciences. They are a new modem and frequency synthesizer
being developed by E-Systems to provide anti-jam capability for the ANIPRC-126
radio and a digital signal processor from Martin Marietta to replace bulky
analog components in the RF Hellfire antitank missile and thus increase the
lethality of its warhead. Each of these projects will require hundreds of
thousands of the new components, he says.
In addition to assuring military program managers of
reliable sources of supply, this increased volume should give the United States
an edge in the inevitable GaAs shoot-out with Japan. Already, four Japanese
companies—NEC, Oki, Hitachi, and Sumitomo —are actively marketing GaAs integrated
circuits in the United States, although these are generally less complex
devices derived from the companies' programs in fiber optics.
There are only two, relatively low-volume, Air Force
projects on the list, but they could have the biggest impact on pushing GaAs
technology. E-Systems in Greenville, Tex., is developing a distributed array
processor for "special mission aircraft" under a contract from the
Air Force Logistics Command that will increase processing speed six-fold while
reducing subsystem weight by 300 pounds. Martin Marietta in Denver is
developing a one-chip on-board spacecraft computer for a classified reconnaissance
satellite that will increase processing speed from 75,000,000 operations a
second to 560,000,000—without changing the system architecture or software.
Vitesse Semiconductor of Camarillo, Calif., is supplying 15,000-gate arrays for
For the Navy, Texas Instruments in Dallas is developing a
GaAs thirty-two-bit computer operating at 200 MHz (two hundred million cycles
per second) to improve the resolution of the AN/APS-137 surface-search radar
on the P-3C patrol aircraft. Under a separate DARPA-sponsored program, the
Navy is also looking at GaAs devices to improve the performance of its Ariadne
undersea antisubmarine warfare system. The devices would reduce power
requirements by a factor of five to ten at each node of the fiber optic cables.
These DARPA-sponsored projects illustrate another edge for
GaAs. Compared to silicon, it has what is known as a speed-power product that
is about six times better. That means you can send the same amount of data
traffic for one-sixth the power (particularly important for spacecraft and, to
a lesser extent, aircraft) or six times as much information for the same electrical
power requirement (a better choice for terrestrial applications). Moreover,
radiation resistance comes for free, which makes GaAs particularly attractive
for military use.
Outside the DARPA program, GigaBit Logic of Newbury Park,
Calif., one of the GaAs chip suppliers, is under contract to the Air Force's
Ballistic Systems Division at Norton AFB, Calif., to develop a GaAs version of
the Air Force's popular 1750 airborne computer. The one-chip, sixteen-bit
microprocessor is intended to be capable of speeds of 1 GHz (a billion cycles
per second) with error correction. GigaBit Logic is teamed with Jaycor, a
company in San Diego that specializes in radiation resistance, and Galaxy
Microsystems, a 1750 architecture design firm in San Jose, Calif., and Austin,
Tex., on the project.
Another small start-up company, Gazelle of Santa Clara,
Calif., has developed a GaAs program logic array that is compatible with
conventional transistor-transistor logic (TTL) but is twice as fast. This array
will replace an entire box in a military system with a single chip.
As is customary in any new technology, costs are initially
high but are plummeting rapidly. Dr. Prabhakar estimates that a three-inch-diameter
wafer costs $160 to $175 and that the processing and testing of the devices
adds another $2,000 per wafer. However, the industry is moving up to four-inch-diameter
wafers, which reduce costs. Mike Pawlik, vice president for marketing at
GigaBit, estimates that twenty suppliers have been qualified on three-inch
wafers and eight on four-inch wafers. The silicon industry has long been
working with five-inch wafers.
GaAs has an inherent cost advantage over silicon at the
processing end. The photolithographic process used to imprint the devices onto
a substrate requires only twelve masking steps for even the most complex GaAs
devices. That corn- pares to twenty or more for comparable silicon devices
made with the complementary metal oxide semiconductor process.
Prices May Drop
In fact, as all the new companies scramble to get on board
this technology, a worldwide drop in GaAs prices may be in the works, according
to Dr. David Miller, a manager at the Litton Airtron Division, Morris Plains,
N. J., one of the principal GaAs wafer suppliers. "Because of all the
hype, the hockey stick [an allusion to steep sales curves in growth industries]
is lying down. It's not straight up," he says. "There's overcapacity
at every level."
Gallium is a material for which the United States is
completely dependent on foreign sources of supply: Canada, France, Germany,
and Japan. "Arsenic is cheap. It's everywhere," says Pawlik of
GigaBit. "Gallium is priced like silver." In addition to Airtron, the
major wafer suppliers include the Canadian conglomerate Cominco (which
extracts gallium as a by-product of aluminum refining), MIA Com of Lowell,
Mass., and the Japanese firms Mitsubishi and Sumitomo.
Dataquest, a market research firm in San Jose, Calif., that
has a reputation for conservative forecasts, projects that the merchant market
for GaAs devices will rise from $328 million this year to nearly $1.3 billion
by 1993. That's a thirty-five percent compound annual growth rate, but about
thirty percent of the total today is accounted for by nonrecurring engineering
costs for technology and product development.
The growth is projected to be fastest for digital GaAs—from
$127 million this year to $656 million in 1993—which is currently dominated
by the "big three" merchant suppliers, GigaBit, TriQuint, and
Vitesse. The market for analog devices (not including those for DARPA's MIMIC
program) is projected to grow from $201 million to $621 million over the same
period. (The figures also do not include the output of the "captive"
suppliers such as AT&T, Hughes, McDonnell Douglas, Rockwell, Texas Instruments,
TRW, and Westinghouse, which produce solely for their own needs.)
The real competition is not among the GaAs producers, according
to Louis Pengue, marketing manager at TriQuint, but against the entrenched
silicon devices, particularly top-of-the-line emitter-coupled logic (ECL),
which has replaced TTL and dominated military systems in recent years. He
calls the problem the "FUD factor" (fear, uncertainty, and doubt),
which he expects to be erased as more program managers become familiar with
the new technology.
Reducing costs is essential to winning acceptance,
according to Mr. Pengue. That means driving down the cost per gate of a large
logic array (10,000 gates or more) to three to five cents so it can compete
head-on with ECL. One of the best ways to do that is to increase the chip size,
and GaAs has been moving up steadily from 100 mils on a side to 200 mils. (One
mil is a thousandth of an inch, so 100 mils is a tenth of an inch.) It needs to
go beyond 300 mils, Mr. Pengue maintains, but he says there's a "fear
threshold" among users at about 250 mils.
If anybody should know the pluses and minuses of GaAs, it's
Seymour Cray, who has been building the world's most powerful supercomputers
for at least twenty years. He laid it all out at last year's Super-computing
'88 conference in Orlando, Fla., cosponsored by the IEEE Computer Society and
the Association for Computing Machinery.
"Gallium arsenide is pretty horrible to work with. It
has a lot of grain," which affects the flow of electrons, he said.
"It's . . . tough to get everything lined up right in order to make the
system function properly," he explained. "It's like working with
potatoes. There are soft spots, hard spots, eyes, and skin—and it's very hard
right now to get good quality basic material to work with. But it gets better
The Cray 3 uses GaAs for all the logic functions (but
silicon devices for memory) to achieve breathtaking speeds of sixteen
gigaflops (that's 16,000,000,000 floating point operations a second). It was
originally scheduled for initial deliveries right about now, but technical
problems and a move of the company from Minneapolis to Colorado Springs, Colo.,
have caused a slip of nearly two years. But already Cray is reported to be
working on an all-GaAs Cray 4 capable of 128 gigaflops.
Out of the Sandbox
Looming over this GaAs free-for-all is the emergence of
indium phosphide. Paul Greiling, manager of gallium arsenide research at the
Hughes Research Laboratories in Malibu, Calif., reported in July on a
high-electron-mobility transistor in which individual layers of indium
phosphide, aluminum indium arsenide, and gallium indium arsenide as thin as
five individual atoms were deposited using the molecular beam epitaxial
The result is a fifteen-fold improvement in sensitivity for
a communications satellite receiver, which means the ground antenna for use
with a direct broadcast satellite could be reduced to one foot in diameter.
Data rates as high as twenty-five gigabits (twenty five billion bits) a second
were achieved. Reasonable extrapolations of this technology could lead to
ultrasensitive radars capable of spotting stealth vehicles—or to the
"Dick Tracy" wristwatch radio.
What may be even more exciting is that the gallium indium
arsenide layer can serve as a laser diode operating at the wavelengths of
1,300 and 1,550 nanometers (billionths of a meter). Those are the wavelengths
of state-of-the-art single-mode optical fibers, which would permit data output
from the computer chip to be in the form of photons rather than electrons. That
would be a big step toward the post-electronics world of photonics (see
"Beyond Electronics," p. 78, June 1989 issue). Nobody is predicting
an end for silicon-based electronics devices, but the industry has begun
venturing cautiously out of its sandbox.
Eleven weapon systems
will be updated with GaAs technology.
Infusions of Arsenic
The Defense Advanced Research Projects Agency (DARPA) this
year selected nine major defense contractors to participate in a program to
insert digital gallium arsenide (GaAs) integrated circuits into eleven
operational weapon systems.
The selection follows a broad agency announcement issued by
DARPA on January 22, 1988, in which the agency sought proposals from industry
on ways to upgrade current silicon-based devices to improve performance.
Supporting the nine prime contractors are three new
companies founded specifically to produce GaAs digital integrated circuits for
military and commercial markets: GigaBit Logic of Newbury Park, Calif.,
TriQuint of Beaverton, Ore., and Vitesse Semiconductor of Camarillo, Calif.
Program manager at DARPA is Dr. Arati Prabhakar, and the
program is under the direction of Sven A. Roosild, assistant director for
electronic sciences in DARPA's Defense Sciences Office. The projects, by
service, are as follows:
Air Force: E-Systems, Greenville (Tex.) Division:
distributed-array processor for special-mission (reconnaissance) aircraft, Air
Force Logistics Command.
Martin Marietta Space Systems, Denver, Cob.: spacecraft
on-board processor for reconnaissance satellites (a "black" program
for which the program office was not disclosed).
Army: E-Systems, ECI Division, St. Petersburg, Fla.: modem
and synthesizer for AN/PRC-126 small unit radio, Army Communications
Electronics Command (C-ECOM).
ITT Avionics, Nutley, N. J.: digital radio frequency memory
for AN/ALQ-136 jammer, C-ECOM.
Martin Marietta Electronic Systems, Orlando, Fla.: signal
processor for RF Hellfire seeker, Army Missile Command.
McDonnell Douglas Electronic Systems, Huntington Beach,
Calif.: mast-mounted sight processor for OH-58D Scout helicopter, Army Aviation
Navy: Grumman, Bethpage, N. Y: radar processor for E-2C
airborne early warning aircraft, Naval Air Systems Command (NavAir).
Honeywell Defense Avionics Systems, Albuquerque, N. M.:
digital map computer for the multiservice V-22 Osprey and other aircraft,
KOR Electronics, Huntington Beach, Calif.: digital radio
frequency memory for AN/ULQ-21 threat jamming simulator, Navy Pacific Missile
Sanders Associates, Nashua, N. H.: digital radio frequency
memory for the AN! ALQ-126B used on several tactical aircraft (perhaps later on
the A-12 advanced tactical aircraft), NavAir.
Texas Instruments Defense Systems and Electronics Group,
Dallas: high-resolution upgrade for the AN/APS-137 surface search radar,
John Rhea is a
free-lance writer living in Woodstock, Va., who specializes in military
technology issues and is a frequent contributor to AIR FORCE Magazine. His book
Department of the Air Force is scheduled to be published this month by Chelsea
House, New York, N. Y.
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