Thin films connect novel oxide materials with silicon chips

Researchers from North Carolina State University (NC State) and the US Army Research Office have developed a way to integrate novel functional materials onto a computer chip, allowing the creation of new smart devices and systems.

The novel functional materials are all oxides and include several types of materials that, until now, could not be integrated with silicon chips. These are: multiferroic materials, which have both ferroelectric and ferromagnetic properties; topological insulators, which act as insulators in bulk but have conductive properties on their surface; and novel ferroelectric materials. They are thought to hold promise for applications including sensors, non-volatile computer memory and microelectromechanical systems (MEMS).

"These novel oxides are normally grown on materials that are not compatible with computing devices," says Jay Narayan, professor of materials science and engineering at NC State and co-author of a paper on the work in Applied Physics Reviews. "We are now able to integrate these materials onto a silicon chip, allowing us to incorporate their functions into electronic devices."

The approach developed by the researchers allows them to integrate the materials onto two platforms, both of which are compatible with silicon: a titanium nitride platform, for use with nitride-based electronics; and yttria-stabilized zirconia, for use with oxide-based electronics. Specifically, the researchers developed a suite of thin films that can serve as a buffer to connect the silicon chip to the relevant novel materials. The exact combination of thin films varies, depending on which novel materials are being used.

"These novel oxides are normally grown on materials that are not compatible with computing devices. We are now able to integrate these materials onto a silicon chip, allowing us to incorporate their functions into electronic devices."Jay Narayan, North Carolina State University

For multiferroic materials, researchers use a combination of four different thin films: titanium nitride, magnesium oxide, strontium oxide and lanthanum strontium manganese oxide. But for topological insulators, they would use a combination of only two thin films: magnesium oxide and titanium nitride.

These thin film buffers align with the crystalline planes in the novel oxide materials, as well as with the planes of the underlying substrate – effectively serving as a communicating layer between the two materials. This approach, called thin film epitaxy, is based on the concept of domain-matching epitaxy, and was first proposed by Narayan in a 2003 paper.

"Integrating these novel materials onto silicon chips makes many things possible," Narayan says. "For example, this allows us to sense or collect data; to manipulate that data; and to calculate a response – all on one compact chip. This makes for faster, more efficient, lighter devices."

Another possible application, Narayan says, is the creation of LEDs on silicon chips, to make ‘smart lights’. Currently, LEDs are made using sapphire substrates, which aren't directly compatible with computing devices. "We've already patented this integration technology, and are currently looking for industry partners to license it," Narayan says.

This story is adapted from material from North Carolina State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.