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One of the most durable semiconductor materials ever made—silicon carbide—has turned out to be one of the most difficult to produce for commercial use.
But Tangali Sudarshan is working hard to change that. The veteran USC electrical engineering professor is engaged in several projects funded by the U.S. Department of Defense aimed at making silicon carbide chips easier to make and more reliable to use.
Common silicon chips used in computers and other electronics devices cannot function reliably in harsh conditions such as high heat or exposure to harsh chemicals and radiation. Scientists have discovered that silicon carbide is nearly immune to such conditions, making it an ideal choice for a new generation of semiconductors that can be used on satellites, in automobile electronics, and in other extreme conditions. But its very toughness makes silicon carbide much less easy to manipulate.
“One of the problems with growing silicon carbide wafers is that there tend to be many micro defects in the material that can have a significant influence on device performance,” Sudarshan said. “We have just applied for a patent for an instrument that can detect these defects and create a map of every chip so that a buyer will know exactly what he’s getting.”
Sudarshan's 20-person team, which includes master’s and Ph.D. students, undergraduate research assistants, and post-doctoral fellows, has also developed a technique for polishing silicon carbide wafers for commercial use. It’s not as simple as it might sound: silicon carbide is commonly used as an abrasive, so polishing the material in its wafer form is like trying to make sandpaper smooth.
“Silicon carbide is grown in ingots, then cut into five or six hundred micron slices with diamond sawblades,” Sudarshan said. “The challenge is to produce a quality surface that’s damage-free. We’ve developed a way to polish the surface and will be providing that service for a fee to commercial clients.”
Sudarshan’s silicon carbide research efforts also include a new process for depositing high-quality films on silicon carbide substrates—a key step in device fabrication. The team also is working on new methods for chemical etching of silicon carbide for device fabrication. Because the substance is hard and chemical resistant, normal methods of chemical etching don’t work, Sudarshan said.
The engineering researchers also are working with U.S. Air Force and Naval research labs to study the electronic properties of silicon carbide for use in different applications. Finally, the team is developing a controlled porosity on the surface of silicon carbide wafers that would allow its use in optical and gas sensors in harsh environments.
“We’ve also discovered that silicon carbide is biocompatible, which means it could be used in implantable biomedical devices without being rejected by the body,” Sudarshan said. “That could open up a lot of new possibilities.”
Several of Sudarshan’s former graduate students formed BandGap Technologies, a Columbia firm that is hard at work growing silicon carbide crystals for commercial possibility. Sudarshan continues to consult with the former students and jointly publish scientific papers with them.
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