It would be hard to imagine a happier success story than silicon-based electronics. In the six decades since Morris Tanenbaum built the first silicon transistor at Bell Labs, engineers have been able to shrink the size of the transistors they put on a silicon chip from microns to nanometers, and increase the density of circuit elements a millionfold. But silicon has an Achilles' heel: When it gets hot, its electrical properties degrade, and chips made from the material fail faster.
Engineers are clever about designing systems that don’t exceed about 125 degrees Celsius, usually by using fans and other cooling systems. But the limitation is especially acute for circuits that have to handle high levels of current, which tend to run hot.
In recent years, however, researchers at GE Research and elsewhere have been developing semiconductors that can withstand temperatures of 200 degrees Celsius. They are using silicon carbide (SiC), a tough material used to make sandpaper and grip tape for skateboards that will in time become the standard replacement for silicon.
But the GE material is different. Systems made using this material, also known as power electronics, are fiendishly difficult to make, but they can handle high-power tasks such as converting direct current to alternating current and vice versa. GE began developing SiC MOSFETs (metal-oxide semiconductor field-effect transistors) more than a decade ago and achieved the strict standards required by the automotive industry. GE has since won dozens of contracts, mostly for military applications.
“Silicon carbide is superior to silicon,” says Rick Eddins, an engineer at GE Aviation Systems. “It has high temperature performance and lower losses, and you can make more efficient systems using it.”
A big advantage of the higher operating temperature is a drastic reduction in the amount of equipment needed to keep the circuits or electronics cool. For instance, as part of several contracts with the U.S. Army, GE Aviation Systems is developing SiC-based products for next-generation ground vehicles, such as mobile artillery and armored transport. By using SiC and operating at higher temperatures and voltages, the Army can reduce the volume of space devoted to fans, coolant, plumbing, radiators, compressors and other gear by a factor of four and have unprecedented power, electronic density and performance.
One such product is a SiC-based DC-DC converter, which would do in one silicon-based unit what is now done by two units in the Army’s Paladin mobile artillery vehicle (which looks like a tank with a cannon on top).“The resulting system has few parts, and therefore fewer points of failure,” Eddins says.
“The path we’re on here is so important,” says Christine Milford, director of business development for power conversion and control. “The government is investing in this. They get it, and they understand how silicon carbide is going to change the future of power electronics. We’re taking our investment money along with theirs and developing products that have broad applications outside the military. We’re expanding into civilian applications that have the same problems, like civilian aerospace systems, healthcare/MRI machines, solar and wind power systems, earth movers and similar challenging environments. That’s where the volume comes in, the price goes down and the adoption is wider.”