Move over graphene, there’s a new 2D wonder material being hailed as a potential Moore’s law extender, called silicine. This one‐atom‐thick two‐dimensional crystal of silicon could be the ultimate miniaturization enabler, setting the stage for future generations of faster, more energy-efficient microchips.
A cousin to graphene, silicine consists of a single layer of atoms arranged in a honeycomb pattern, but where graphene is carbon-based, silicine is made from silicon atoms. Thus it offers an easier path to integration for a microelectronics industry already dominated by silicon.
Traditional silicon-based transistors can only get down to about 5 atoms thick before becoming unpredictable and losing performance, the invention of a silicene transistor pushes that limitation back to just one atom. And in computing, smaller means faster.
Silicine has had a rather remarkable journey. First theorized in 1994, it wasn’t until 2010 that researchers began making headway in developing the silicon analogue to graphene. Two years later, several teams around the world independently succeeded in creating silicine in the lab.
Now researchers at the University of Texas at Austin’s Cockrell School of Engineering are unveiling details of the first silicene transistor, a crucial characteristic for logic operations.
The devices were developed by Deji Akinwande, an assistant professor in the Cockrell School’s Department of Electrical and Computer Engineering, and his team, which includes lead researcher Li Tao. Their demonstration that silicine can be made into transistors is a major advancement in the search for alternative CMOS materials.
“Nobody could have expected that in such a short time, something that didn’t exist could make a transistor,” says Guy Le Lay, a materials scientist at Aix-Marseille University in France, who was one of the first scientists to create silicine.
Despite its promise, there are major challenges associated with silicene, such as its instability when exposed to air.
To reduce exposure to air, the researchers formed a silicene sheet by allowing a hot vapor of silicon atoms to condense onto a crystalline block of silver inside a vacuum chamber, then added a 5-nanometer-thick layer of alumina on top. Thus protected, the team was able to safely peel it of its base and transfer it to an oxidized-silicon substrate. By scraping off some of the silver, the team exposed two islands of metal (acting as electrodes) with a strip of silicene between them.
The exposed silicine still degrades in about two minutes, but that window of time was sufficient to measure its properties. While its electrons were “sluggish” in comparison with graphene, silicine’s buckled structure endows it with a tuneable band gap, which graphene, being flat, lacks. Since band gaps are what give semiconductors the ability to switch currents on and off, they are the foundation of transistors.
The technique shows promise for other paper-thin, air-sensitive materials too, but its silicon-nature makes silicine a serious contender for commercial adoption.
“Apart from introducing a new player in the playground of 2-D materials, silicene, with its close chemical affinity to silicon, suggests an opportunity in the road map of the semiconductor industry,” Akinwande said. “The major breakthrough here is the efficient low-temperature manufacturing and fabrication of silicene devices for the first time.”