New transistors can make electronics cheaper, more efficient

Saturday, Aug 1, 2015,18:37 IST By metro vaartha A A A

Washington | A material called gallium nitride (GaN) is poised to become the next semiconductor for power electronics, enabling much higher efficiency than silicon. Massachusetts Institute of Technology spinout Cambridge Electronics Inc (CEI) has announced a line of GaN transistors and power electronic circuits that promise to cut energy usage in data centres, electric cars, and consumer devices by 10 to 20 per cent worldwide by 2025.
Many of these power-electronics systems rely on silicon transistors that switch on and off to regulate voltage but, due to speed and resistance constraints, waste energy as heat. CEI’s GaN transistors have at least one-tenth the resistance of such silicon-based transistors, which allows for much higher energy-efficiency.
While GaN transistors have several benefits over silicon, safety drawbacks and expensive manufacturing methods have largely kept them off the market. The researchers managed to overcome these issues. Power transistors are designed to flow high currents when on, and to block high voltages when off. But GaN transistors are typically ‘normally on’  meaning, by default, they’ll always allow a flow of current.
The researchers developed GaN transistors that were ‘normally off’ by modifying the structure of the material. 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, said CEI co-founder Tomas Palacios, an MIT associate professor who co-invented the technology.
To drop manufacturing costs, the researchers developed new fabrication technologies which involved switching out gold metals used in manufacturing GaN devices for metals that were compatible with silicon fabrication, and developing ways to deposit GaN on large wafers used by silicon foundries.
CEI is currently using its advanced transistors to develop laptop power adaptors that are approximately 1.5 cubic inches in volume  the smallest ever made. Among the other feasible applications for the transistors is better power electronics for data centres run by Google, Amazon, Facebook, and other companies, to power the cloud.
Currently, these data centres eat up about 2 per cent of electricity in the US. But GaN-based power electronics, Palacios said, could save a very significant fraction of that. Another application will be replacing the silicon-based power electronics in electric car, Palacios said. These are in the battery chargers 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, the researchers said. GaN-based power electronics, on the other hand, could boost power output for electric cars, while making them more energy-efficient and lighter  and, therefore, cheaper and capable of driving longer distances.

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