A team of U.S. researchers announced Thursday they had succeeded in creating the world’s smallest transistor, breaking what had previously been perceived an insurmountable barrier in transistor size. The experimental device, which has a functional 1-nanometer gate, was built using carbon nanotubes and molybdenum disulfide rather than silicon — the material transistors in today’s electronic devices are made of. For comparison, a human hair is roughly 80,000 to 100,000 nanometers wide.
“Silicon transistors are approaching their size limit,” Moon Kim, a professor of materials science and engineering at the University of Texas at Dallas, and an author of a study detailing the creation of the transistor, said in a statement. “Our research provides new insight into the feasibility to go beyond the ultimate scaling limit of silicon-based transistor technology.”
When current flows through a transistor, a stream of electrons moves through a channel. The gate controls this movement, shutting the flow on and off as required.
Silicon — a semiconductor — has long been used to make transistors because it facilitates the free flow of electrons in a way that can be easily controlled through a process known as “doping.” However, the problem with silicon transistors is that there is a limit to how small they can be. The laws of physics set a 5-nanometer threshold on the size of silicon-based transistor gates, after which a phenomenon known as quantum tunneling makes it impossible to control the flow of electrons through them.
“This means we can’t turn off the transistors,” lead author Sujay Desai from the University of California Berkeley and the Lawrence Berkeley National Laboratory, said in a statement. “The electrons are out of control.”
The size limit also places a restriction on the number of transistors that can be placed in an integrated circuit, thereby threatening the survival of Moore’s Law — which states that the number of transistors in a semiconductor circuit doubles every two years — and crimping processor speeds.
“As of today, the best/smallest silicon transistor devices commercially available have a gate length larger than 10 nanometers,” Kim said. “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. What this means, for example, is that a cellphone with this technology built in would not have to be recharged as often.”
Using molybdenum disulfide — an engine lubricant commonly sold in auto parts shops — provides a key advantage, its comparatively high resistance allowing scientists to control the flow of electrons even with smaller gate lengths.
Currently, this is just a proof of concept. The researchers cautioned there are several “technical challenges” that need to be overcome before large-scale manufacture of such transistors becomes possible.
“We have not yet packed these transistors onto a chip, and we haven’t done this billions of times over,” co-author Ali Javey from the Berkeley Lab said. “But this work is important to show that we are no longer limited to a 5-nanometer gate for our transistors. Moore’s Law can continue a while longer by proper engineering of the semiconductor material and device architecture.”