MIT develops hybrid chip

An MIT team has succeeded in creating a hybrid chip, combining silicon and gallium nitride.

Processor speed is dependent on size. “We won’t be able to continue improving silicon by scaling it down for long,” Tomas Palacios, assistant professor in the Department of Electrical Engineering and Computer Science said: “It’s very difficult to make them a lot smaller.”

One answer is to use new advanced materials for the transistors. “There are several semiconductor materials that offer better performance than silicon,” Palacios says. “The problem is, even though they allow for very fast transistors, they cannot compete with silicon in terms of integration and scalability.”

But combining two different kinds of materials on a single, hybrid chip would allow conventional silicon to provide the vast majority of the transistors, while a material with better performance would be used for those that need to work faster.

Instead of trying to grow the high-performance semiconductor material on top of a silicon chip, as others have attempted, the MIT team embedded a gallium nitride layer into a standard silicon substrate. This not only produces a faster chip, but one that is highly efficient, and means the chips can be manufactured using standard processes.

Thomas Kazior, technical director of Advanced Microelectronics Technology at Raytheon Integrated Defense Systems, said the new advance addresses some of the present limitations of both silicon and gallium nitride technology. This could “enable a new class of high-performance mixed-signal and digitally controlled RF [radio frequency] circuits for use in a wide range of Department of Defense and commercial applications,” he said.

Such hybrid chips could also lead to much more efficient cell phone manufacturing, Palacios said.

At present, the new technique has been used to make chips that are about one square inch in size. Conventional chip manufacturing processes typically uses eight or 12-inch wafers. “We have several ideas in that direction,” Palacios said. “We are already discussing with several companies how to commercialize this technology and fabricate more complex circuits.”

The results will appear in the IEEE journal Electron Device Letters.