American researchers have discovered a material that allows reversibly changing electrical resistance as efficiently as silicon transistors but on a scale of electrons.
The material, a correlated oxide called samarium nickelate, performs well at room temperature as well as at several hundred degrees Celsius, making it suitable for integration into existing electronic devices and fabrication methods.
Hailed one of the best possible alternatives to silicon, the innovative material has been described in a study by Harvard School of Engineering and Applied Sciences (SEAS) researchers in the recent issue of the journal Nature Communications.
“Traditional silicon transistors have fundamental scaling limitations. If you shrink them beyond a certain minimum feature size, they don't quite behave as they should,” said one of the study’s authors Shriram Ramanathan, Associate Professor of Materials Science at SEAS.
Until today, available alternatives offered insufficient on-off ratios. Whereas the minimum required for practical use is 104, even the best correlated oxides have previously achieved 100 at best. The newly discovered samarium nickelate transistor provided an on/off ratio of more than 105, which is comparable with state-of-the-art silicon-based devices.
“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 said.
To create the orbital transistor, the researchers have used doping, introducing different atoms into the crystal structure of the material to make its electrons move around more easily. The ability of electrons to move through the material has a direct effect on the material’s ability to resist or conduct electricity. In this case, the Harvard team manipulated the band gap, the energy barrier to electron flow.
“By a certain choice of dopants – in this case, hydrogen or lithium – we can widen or narrow the band gap in this material, deterministically moving electrons in and out of their orbitals,” Ramanathan said.
In the orbital transistor, protons and electrons move in or out of the samarium nickelate when an electric field is applied, regardless of temperature, so the device can be operated in the same conditions as conventional electronics. It involves no liquids, gases, or moving mechanical parts and in the absence of power, the material remembers its present state – an important feature for energy efficiency.
Material scientists have been studying the family of correlated oxides for years, but the field is still in its infancy, with most research aimed at establishing the materials’ basic physical properties.
“We have just discovered how to dope these materials, which is a foundational step in the use of any semiconductor,” said Ramanathan.
Samarium nickelate is likely to catch the attention of applied physicists developing photonic and optoelectronic devices.
“Opening and closing the band gap means you can now manipulate the ways in which electromagnetic radiation interacts with your material,” said Jian Shi, a postdoctoral fellow in Ramanathan’s lab at Harvard SEAS. “Just by applying an electric field, you’re dynamically controlling how light interacts with this material.”
However, the researchers say, the field is still in its infancy, about as advanced as was the transistor technology in the 1950s.