New material has potential to out-silicon silicon
July 31, 2015 | By
Jaclyn Brandt
A new material is being called the new silicon, and it has such potential the Department of Energy (DOE) is spending millions to research it.
Gallium nitride (GaN) is said to be the next important semiconductor for power electronics -- mostly because it enables a much higher efficiency than silicon. DOE invested around $70 million back in 2013 to a research institute for power electronics for GaN research. The funds were around half of the $140 million cost for the center. From that, Massachusetts Institute of Technology (MIT) company Cambridge Electronics Inc. (CEI) has released a line of GaN transistors and power electronics circuits, with the goal of cutting energy use across the world, in data centers, electric cars, and consumer devices -- by 10 to 20 percent worldwide by 2025. Power electronics is used to convert electricity to higher or lower voltages and different currents -- like in an electric substation -- and many of these systems rely on silicon transistors to regulate voltage. The downside of silicon is that it wastes energy as heat due to speed and resistance constraints. "CEI's GaN transistors have at least one-tenth the resistance of such silicon-based transistors," said the MIT Energy Institute (MITEI) in a statement. "This allows for much higher energy-efficiency, and orders-of-magnitude faster switching frequency -- meaning power-electronics systems with these components can be made much smaller." CEI is focused on creating transistors that can help data centers use less energy by enabling power electronics. This could also help lower prices for electric vehicles (EV) and make power adapters up to one-third smaller. "This is a once-in-a-lifetime opportunity to change electronics and to really make an impact on how energy is used in the world," said CEI co-founder Tomás Palacios, an MIT associate professor of electrical engineering and computer science, in a statement. Although GaN may seem like a flawless material, it has stayed largely off the market because of safety issues and expensive manufacturing. But MIT researchers have helped remove these barriers. "Power transistors are designed to flow high currents when on, and to block high voltages when off. Should the circuit break or fail, the transistors must default to the "off" position to cut the current to avoid short circuits and other issues -- an important feature of silicon power transistors," MITEI said. "But GaN transistors are typically 'normally on' -- meaning, by default, they'll always allow a flow of current, which has historically been difficult to correct. Using resources in MIT's Microsystems Technology Laboratory, the researchers -- supported by Department of Defense and DOE grants -- developed GaN transistors that were "normally off" by modifying the structure of the material." GaN transistors are normally made by growing a thin layer of GaN on top of a substrate. However, the MIT researchers layered different materials with disparate compositions in their GaN transistors. "We always talk about GaN as gallium and nitrogen, but you can modify the basic GaN material, add impurities and other elements, to change its properties," Palacios said. To reduce manufacturing costs for GaN the researchers at MIT developed fabrication "process recipes" that would replace gold materials with depositing GaN on large wafers. "Basically, we are fabricating our advanced GaN transistors and circuits in conventional silicon foundries, at the cost of silicon. The cost is the same, but the performance of the new devices is 100 times better," Lu explained. At CEI, the researchers are developing 1.5 cubic inch power adaptors that can be used for data centers -- which use around 2 percent of electricity in the US. "Another major future application... will be replacing the silicon-based power electronics in electric cars," MITEI explained. "These are in the chargers that charge the battery, and the inverters that convert the battery power to drive the electric motors. The silicon transistors used today have a constrained power capability that limits how much power the car can handle. This is one of the main reasons why there are few large electric vehicles." However, power electrons using GaN could help make EVs smaller and more energy efficient. Palacios explained, "Electric vehicles are popular, but still a niche product. GaN power electronics will be key to make them mainstream." To launch CEI, Palacios used MIT's Innovation Teams program, which brings MIT students to the research team to produce commercially-feasible products. For more:
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