Diamond Transistors

Power Electronics INSIDER

Researchers at Arizona State University and Northrop Grumman are working on a new project to create power transistors from diamond. The results could yield efficiencies that significantly shrink the size of electrical grid substations and potentially drop the cost of cell phone towers.

Power transistors have traditionally been made with silicon. But the ASU Advanced Materials team, working with Northrop Grumman Mission Systems, is investigating diamond because it dissipates heat 8 to 10 times more efficiently than current materials. This means harnessing diamond to its full potential could reduce the size of power transistors by 90 percent.

Diamond also has a high breakdown field, meaning it can handle a large amount of voltage relative to most other materials, before failure. A high breakdown field is ideal for applications that handle large amounts of power, which could make these new transistors vital to advancing our transition to renewable energy and electrification of the transportation sector.

Silicon has long been the standard material for semiconductor devices. Power transistors regulate the flow of electrical power and have traditionally been made with silicon, while more advanced modern transistors are made of materials such as silicon carbide or gallium nitride.

Trevor Thornton , a professor of electrical engineering in the Ira A. Fulton Schools of Engineering at Arizona State University, is leading a team researching the use of two new transistor materials: diamond and boron nitride.

While diamond is the research team's chosen material for the main body of a transistor, they are investigating the use of boron nitride for the transistors’ electrical contacts. Like diamond, boron nitride has a high breakdown field and high thermal conductivity.

The research team expects that by combining their knowledge of how diamond and boron nitride work as transistor materials, they can create transistors made from both materials. The team's hope is that the materials complement each other and work even better together than individually.

This research has applications that would be especially useful to communications technologies. Many satellites, for example, run on solar power, which requires transistors to turn the electricity into a form usable by the satellite.

"You can't launch a power substation into space," Thornton said. "So, any improvement on size and weight in a satellite has a huge impact."

Other communications technology the transistors could improve is a bit closer to home: cell phone towers. Transistors convert power to the proper form needed to produce the radio frequencies that cell phones use.

Thornton said that one of the biggest challenges faced when designing and operating cell phone towers is keeping them cool. This is especially the case in a hot environment like Phoenix.

The power transistors in older cell phone towers are typically made from silicon, while those in newer 5G systems will use gallium nitride. Thanks to their improved heat dissipation, Thornton's team expects transistors made from diamond and boron nitride to greatly reduce the cooling power needed for cell towers. This makes the task of keeping cell towers from overheating far easier.

While the project with Northrop Grumman Mission Systems focuses on communications technology, transistors made from diamond and boron nitride also have applications in power conversion for electrical systems and for the electricity grid. These more efficient materials could reduce the size requirements for electricity grid substations. Substations typically take up an area of land the size of a building. "We’d like to make them smaller and more efficient," said Thornton.

Robert Nemanich, a faculty member in the ASU Department of Physics, leads a group conducting research on power electronics called the ULTRA Energy Frontier Research Center. He also leads a lab for growing artificial diamond material, which will be used by Thornton's team in their research. "We have been growing diamond for electronic devices for the last 10 years," Nemanich said. "We believe our diamond deposition lab has unique capabilities for the development of electronic materials and devices."

In addition to Thornton's electrical engineering expertise and Nemanich's work with diamond as an electronic material, Terry Alford, another faculty member in the Fulton Schools, provides his expertise on materials science. Alford is working on materials characterization, analyzing the properties of the materials the team is investigating. He also leads a part of the research looking into the use of new types of metallic electrical contacts connected to diamond as a substrate.

The transistor research project is funded for two years through their partnership with Northrop Grumman Mission Systems. However, to fully realize the transistors’ potential for widespread applications, Thornton said it could take longer.

"We’ll have breakthroughs, but I don't see it being widely adopted in the way we’re talking about for five to 10 years," he says. "It's that kind of medium- to long-term research for which some applications will happen quicker, while others will be 10 years for widespread consumer applications."

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