Inside the Diamond Mine: Synthetic Gems
Diamonds may no longer be just a girl’s best friend. Sixty years after Marilyn Monroe’s musical ode to them, the military is showing interest in the synthetic version of these classic gems.
Sheets of laboratory-grown diamond, combined with the semiconductor gallium nitride (GaN), could someday become the core of future-generation radar, communications and electronic warfare systems. Such components could save huge amounts of electricity, space and fuel.
"Diamonds aren't just pretty," said Ralph Korenstein, who runs Raytheon's diamond laboratory in Andover, Mass. "They have a practical use. You can see farther, you can get more power."
Inside the Diamondworks
Raytheon's "diamond mine" lies deep inside the Integrated Air Defense Center, the sprawling factory 20 miles northwest of Boston that produces some of Raytheon's best-known products, including the Patriot air and missile defense system and the AN/TPY-2 radar.
The diamond lab is famous among workers at the plant, especially around Valentine's Day.
"I've had several guys who are getting engaged say, `Hey, can you grow me a diamond for my ring?'" Korenstein said.
Workers in the lab used to have a poster of Disney's Seven Dwarfs – fellow diamond miners – hanging on the wall with a sign that said "Diamonds ‘R' Us."
To make diamond, engineers pump microwaves into metal reactors filled with hydrogen and methane, heating the gases into a glowing green ball of plasma. Soon the carbon in the methane begins to form into diamond crystals that collect on a metal plate.
Engineers actually used a kitchen microwave oven to make Raytheon's first diamond reactor, Korenstein said. The production version uses an industrial microwave.
"They used to sell that to cook hot dogs or whatever," Korenstein said.
Engineers can speed up the process by spraying the metal plate with diamond "seeds." They've even put jewelry-grade diamonds into the reactor and doubled their size.
It takes about a month to grow a five-inch-wide disc of the highest-quality diamond. Workers polish the disc using more diamond, then use a laser to cut it into thousands of chips.
That thermal conductivity is what intrigues the military. In 2012 the Defense Advanced Projects Research Agency, or DARPA, contracted Raytheon to develop a new generation of gallium nitride devices by bonding them to pieces of diamond to improve cooling.
Raytheon is already a leader in gallium nitride components, which can emit five times the radio energy of the previous technology, gallium arsenide. The gallium nitride technology promises to revolutionize radars, jammers and communications gear.
"It enables more reliable systems with less weight and space, which translates into fuel savings and lower maintenance costs – saving money over the life of the system." said Colin Whelan technical director of Advanced Technology Programs at Raytheon Integrated Defense Systems.
The technology also allows customers to fit higher performance radars into existing planes and ships, an important advantage in an era of tight government budgets.
"Pockets aren't as deep as they once were," said Joseph Biondi, vice president of Advanced Technology Programs at Raytheon Integrated Defense Systems. "This technology enables us to keep bringing high-performance solutions to our customers who need it, but within a price range that they can live with."
However, gallium nitride components also create tremendous amounts of heat that must be conducted away. So engineers bond the components to diamond or other advanced materials.
"Whenever the juncture temperature is still too high, it's vital to locate a better heat-spreader material," said Linda Wagner, a senior director of Raytheon's Radio Frequency Components business. "Diamond is perfect for this as a replacement for a more conventional heat spreader."
Raytheon's diamond has also found its way into other kinds of electronics, including instruments on the Mars rovers Spirit and Opportunity.
As Raytheon's diamond operation attracts more attention, Korenstein said he's gotten used to the co-workers who jokingly request earrings or a ring.
"I have people try to put in orders with me," Korenstein said. "But we're not in the jewelry business."