IEEE 2014 Medal of Honor Recipient Comes from the Field of Power Semiconductors
B. Jayant Baliga, originally from the outskirts of Bangalone, India, is this year’s IEEE Medal of Honor recipient. Science and engineering were a part of Baliga’s life from an early age. His father, one of India’s preeminent electrical engineers, was chairman and managing director of Bharat Electronics Limited. Baliga developed his interest in science, especially electrical engineering, by immersing himself in his father’s technical library. Later he studied electrical engineering at the Indian Institute of Technology Madras. While studying there Baliga found a subject that interested him even more, physics, but switching majors was not an option. He decided to combine his interests and study semiconductors. Wanting to avoid living under his father’s shadow, Baliga decided to continue his studies of semiconductors abroad at Rensselaer Polytechnic Institute (RPI) in Troy, New York.
As a master student studying under Sorab K. Ghandhi, Baliga worked on gallium arsenide semiconductors. During his Ph.D. work he investigated a technique he could use for growing indium arsenide and gallium indium arsenide semiconductors, a process now known as metal-organic chemical vapor deposition. This research was extremely dangerous, as the compounds involved would detonate when exposed to air. Ghandhi was not detoured, and counseled his student to build a reaction vessel that was “really tight”. After earning his Ph.D. in 1974, Baliga hoped to acquire a research position with IBM or Bell Laboratories. However, with only a student visa, Baliga was not able to get an interview with either institution. A fellow graduate student at RPI, who was also working for General Electric Research Laboratory, told him about a position investigating power devices. Baliga was not thrilled with the possibility of working with power devices, believing that all the interesting work had already been done. With no other options, Baliga applied and got the job.
Baliga’s early work for GE involved thyristors-semiconductor devices, which are now mostly used for handling extremely high voltages. During his studies, Baliga thought it may be possible to get them to work like regular transistors, which can be switched on and off on command. GE had the need for energy-saving variable-frequency motor drives, and Baliga designed a thyristor-like device that combined attributes of MOSFETs and bipolar transistors. At this time these semiconductors had not been combined.
Baliga’s colleagues shared his idea with GE’s chairman and CEO, Jack F. Welch Jr., and in 1981 Welch traveled to GE’s research center to be briefed on the new transistor concept. The meeting went well and within a year the team was fabricating wafers with the new design. Originally the device was named the “insulated-gate rectifier,” in an attempt to distinguish it from ordinary transistors. Later Baliga changed with name to insulated-gate bipolar transistor (IGBT) as to not confuse application engineers.
The IGBT was successful in avoiding catastrophic “latch up” – the thyristor-like continuation of current flow after a transistor is turned off. However, it was still switching off too slowly to be used for variable-frequency motor drives. Known methods of upping the speed of a transistor would ruin this type of MOS device. Baliga created a way to speed up the IGBT: electron irradiation. While this method had been used on bipolar power rectifiers, it damaged the MOS device. Baliga figured out a way to apply enough heat to repair the damaged done to the MOS structure while keeping the speed boost.
After one of GE’s investments went badly, Welch decided to sell off GE’s entire semiconductor business in 1988, leaving Baliga’s expertise useless to the company. While Baliga was ensured he would have a position in management, his heart was still in science. With other offers holding little promise, and the academic activity in power devices nonexistent in the United States, Baliga chose to create his own research program. In 1988 Baliga moved to North Carolina State, where he has taught and done research for 25 years now. Recently, President Obama visited to announce the creation of the Next Generation Power Electronics Innovation Institute and a $140 million US grant to the university that Baliga and his team at the university’s Future Renewable Electric Energy Delivery and Management Systems Center helped to win.
One of the goals of the new institute is to speed the development of MOSFETs and other power devices made with wide-bandgap semiconductors. In the future wide-bandgap MOSFETs should be cheap and reliable enough to replace IGBTs. Baliga is ok with this potential outcome. While he’s the creator of the silicon IGBT, a narrow-bandgap device, Baliga has always supported wide-bandgap devices as well. While developing the IGBT at GE, he was also creating the first wide-bandgap power semiconductor, a gallium arsenide rectifier. During this time he also created a way to calculate from basic theory what semiconductor types function best for power devices. This expression is now known as Baliga’s figure of merit, and highlights the potential of silicon carbide and other wide-bandgap semiconductors. The challenge, and what Baliga and his students are actively pursuing, is a way to make these devices cheap enough to compete with silicon.
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Schneider, David. (2014, May). The Power Broker. IEEE Spectrum, 52-58.