Qingxiao Wang (left) and Moon Kim (right) used the atomic resolution electron microscope at UT Dallas to characterize the tiny transistor, just 1nm in size. Photo: UT Dallas.
Qingxiao Wang (left) and Moon Kim (right) used the atomic resolution electron microscope at UT Dallas to characterize the tiny transistor, just 1nm in size. Photo: UT Dallas.

In the quest for faster and more powerful computers and consumer electronics, big advances come in small packages. Over the years, the high-performance, silicon-based transistors that control today's electronic devices have steadily been getting smaller and smaller, allowing those devices to perform faster while consuming less power.

But even silicon has its limits, so researchers at The University of Texas at Dallas and elsewhere are looking for better-performing alternatives. In a new paper published in Science, UT Dallas engineers and their colleagues describe a novel transistor made with a new combination of materials that is even smaller than the smallest possible silicon-based transistor.

"Silicon transistors are approaching their size limit," explained Moon Kim, professor of materials science and engineering at UT Dallas and an author of the study. "Our research provides new insight into the feasibility to go beyond the ultimate scaling limit of silicon-based transistor technology."

The study authors also included Kim's graduate student Qingxiao Wang, together with collaborators at the University of California, Berkeley, Stanford University and the Lawrence Berkeley National Laboratory, which led the project. Researchers in California fabricated the transistor and performed theoretical simulations, while the UT Dallas team physically characterized the device using an atomic resolution electron microscope on campus.

When current flows through a transistor, a stream of electrons travels through a channel, like tap water flowing through a faucet out into a sink. A ‘gate’ in the transistor controls the flow of electrons, shutting the flow off and on in a fraction of second, allowing the transistor to act like a tiny switch.

"As of today, the best/smallest silicon transistor devices commercially available have a gate length larger than 10nm," said Kim. "The theoretical lower limit for silicon transistors is about 5nm. The device we demonstrate in this article has a gate size of 1nm, about one order of magnitude smaller. It should be possible to reduce the size of a computer chip significantly utilizing this configuration."

One of the challenges in designing such small transistors is that electrons can randomly tunnel through a gate when the current is supposed to be shut off. Reducing this current leakage is a priority.

"The device we demonstrated shows more than two orders of magnitude reduction in leakage current compared to its silicon counterpart, which results in reduced power consumption," Kim said. "What this means, for example, is that a cellphone with this technology built in would not have to be recharged as often."

Instead of using silicon, the researchers built their prototype device with a type of two-dimensional semiconductor material known as a transition metal dichalcogenide (TMDs). Specifically, their experimental device structure used a TMD called molybdenum disulfide for the channel material and a single-walled carbon nanotube for the gate.

Kim said that many technical challenges need to be solved before large-scale manufacturing of the new transistor is practical or even possible. "Large-scale processing and manufacturing of TMD devices down to such small gate lengths will require future innovations," he said.

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