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  Date: 10/08/2015

MIT researchers fabricate reliable GaN power transistors at low cost

There are hardly any electronic devices, which doesn't require power conversion from one voltage to other voltage and most of the times, the conversion is from AC voltage source to DC voltage source in personal digital devices. For each of such billions of digital electronics devices, you compulsorily need voltage rectifying diodes, power switching transistors, and transformers. You need at least twice the number of diodes and twice the number of transistors to power each of the digital device we use. That's a huge market for power semiconductor devices.

Most of the diodes and transistors today are made up of the popular silicon material. The power conversion efficiency is in the range of 80 to 95% depending on the architecture of power conversion and also the load requirements. With the Internet of things (IoT) market growing into not just billions, but tens of billions of digital devices. An increment of even 0.1% efficiency improvement in power conversion will result in big saving in power. The use of silicon -based power semiconductor devices can only push the efficiency up to 95% and also they have the limitations when it comes to size of the device and also the switching speeds.

The power semiconductor industry successfully explored two important materials to achieve higher power efficiency, small size and also faster switching. The two materials are Silicon Carbide (SiC) and Gallium Nitride (GaN). To give a simple example of potential benefit of SiC and GaN, the present AC/DC adapter of a notebook computer can be packed with in a size of mobile phone charger by using Silicon Carbide and Gallium Nitride power semiconductor devices. Silicon Carbide is already popular in solar power conversion, electric automotive and many such conversion applications. Gallium Nitride had some issues related to cost and also yield. They have been overcome recently. And now you have a company making GaN power semiconductor devices with the name "Efficient Power Conversion (EPC)" The EPC is offering GaN power semiconductor devices at a cost equal to Silicon power semiconductor devices. EPC founder CEO Alex Lidow need to be appreciated for the early effort in bringing the GaN device from lab to factory.

Added to this is the latest announcement by a start-up company called Cambridge Electronics Inc. (CEI), a spin out of Massachusetts Institute of Technology (MIT), which has announced GaN power switching transistors.

CEI says the on-resistance of its GaN transistors is 10 times less than silicon-based transistors. The founders of this company who are also MIT researchers able to precisely mix different semiconductor materials and deposit in the form of layers to achieve reliable switch-off of the transistor in default mode.

These researchers could reduce the manufacturing cost of non-silicon semiconductor materials by developing new fabrication technologies. Example they could use less expensive metals instead of gold in manufacturing GaN devices and they could deposit Gallium Nitride on silicon using the processes which are less expensive.

“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” comments one of the founder of CEI.

The founders of CEI includes Tomás Palacios, an MIT associate professor of electrical engineering and computer science, Anantha Chandrakasan, the Joseph F. and Nancy P. Keithley Professor in Electrical Engineering, now chair of CEI’s technical advisory board; alumnus Bin Lu SM ’07, PhD ’13, CEI’s vice president for device development; Ling Xia PhD’12, CEI’s director of operations; Mohamed Azize, CEI’s director of epitaxy; and Omair Saadat PhD ’14, CEI’s director of product reliability.

As per our analysis EPC, the earlier entrant in this market also used a similar process in achieving low-cost manufacturing of gallium nitride power semiconductor devices.

GaN semiconductor devices not only improves the power conversion efficiency of AC/DC adapters of personal digital devices. The solar power, electric cars, data centres and any such applications requiring power conversion from AC to DC and DC to AC will benefit hugely by moving over to Gallium Nitride -based semiconductor switching.
Author: Srinivasa Reddy N
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