For electronics beyond silicon, a new contender emerges

During fabrication, the annealing process injects hydrogen ions into thin films of samarium nickelate (SNO) and yttrium-doped barium zirconate (BYZ). During operation, an electric field moves the charges from one layer to the other, and the influx or loss of electrons modulates the band gap in the SNO, resulting in a very dramatic change in conductivity. (Image courtesy of Jian Shi.)

NEW TRANSISTOR ACHIEVES ‘COLOSSAL’ SWITCHABLE RESISTANCE USING QUANTUM MATERIALS AND PHYSICS DEVELOPED IN A FUEL CELL LAB

Silicon has few serious competitors as the material of choice in the electronics industry. Yet transistors, the switchable valves that control the flow of electrons in a circuit, cannot simply keep shrinking to meet the needs of powerful, compact devices; physical limitations like energy consumption and heat dissipation are too significant.

Now, using a quantum material called a correlated oxide, Harvard researchers have achieved a reversible change in electrical resistance of eight orders of magnitude, a result the researchers are calling “colossal.” In short, they have engineered this material to perform comparably with the best silicon switches.

The finding arose in what may seem an unlikely spot: a laboratory usually devoted to studying fuel cells—the kind that run on methane or hydrogen—led by Shriram Ramanathan, Associate Professor of Materials Science at the Harvard School of Engineering and Applied Sciences (SEAS). The researchers’ familiarity with thin films and ionic transport enabled them to exploit chemistry, rather than temperature, to achieve the dramatic result.

Because the correlated oxides can function equally well at room temperature or a few hundred degrees above it, it would be easy to integrate them into existing electronic devices and fabrication methods. The discovery, published in Nature Communications, therefore firmly establishes correlated oxides as promising semiconductors for future three-dimensional integrated circuits as well as for adaptive, tunable photonic devices.

Challenging silicon

Although electronics manufacturers continue to pack greater speed and functionality into smaller packages, the performance of silicon-based components will soon hit a wall.

“Traditional silicon transistors have fundamental scaling limitations,” says Ramanathan. “If you shrink them beyond a certain minimum feature size, they don’t quite behave as they should.”

Yet silicon transistors are hard to beat, with an on/off ratio of at least 10⁴ required for practical use. “It’s a pretty high bar to cross,” Ramanathan explains, adding that until now, experiments using correlated oxides have produced changes of only about a factor of 10, or 100 at most, near room temperature. But Ramanathan and his team have crafted a new transistor, made primarily of an oxide called samarium nickelate, that in practical operation achieves an on/off ratio of greater than 10⁵—that is, comparable to state-of-the-art silicon transistors.

In future work the researchers will investigate the device’s switching dynamics and power dissipation; meanwhile, this advance represents an important proof of concept.

“Our orbital transistor could really push the frontiers of this field and say, you know what? This is a material that can challenge silicon,” Ramanathan says.

Read more . . .