09 September 2013

Researchers Construct Graphene-Based Chips – With An Assist From DNA Molecules

Image Caption: To the right is a honeycomb of graphene atoms. To the left is a double strand of DNA. The white spheres represent copper ions integral to the chemical assembly process. The fire represents the heat that is an essential ingredient in the technique. Credit: Anatoliy Sokolov 

DNA molecules contain the genetic instructions essential to the development and function of living organisms, but new research suggests that they could also play a key role in the future of computer chips.

Researchers from Stanford University believe that DNA could become the template of next generation microchips constructed from an experimental substance known as graphene, which is a one atom thick sheet of carbon atoms arrayed in a honeycomb pattern.

Engineers believe that graphene could be a better semiconductor than silicon, and new research led by Stanford chemical engineering professor Zhenan Bao suggests that the nucleotide polymers that contain our genetic code could help assemble graphene transistors.

In a recent edition of the journal Nature Communications, Bao and her colleagues describe how they set out to solve one of the great problems currently surrounding the future of the electronics industry: the demand for smaller, faster and cheaper silicon chips.

However, despite that demand, the nature of how silicon chips work could hamper the development of such highly-sought after products, explained Stanford School of Engineering associate director of communications Tom Abate.

“Everything starts with the notion of the semiconductor, a type of material that can be induced to either conduct or stop the flow of electricity. Silicon has long been the most popular semiconductor material used to make chips,” he said. “The basic working unit on a chip is the transistor. Transistors are tiny gates that switch electricity on or off, creating the zeroes and ones that run software.”

“To build more powerful chips, designers have done two things at the same time: they’ve shrunk transistors in size and also swung those gates open and shut faster and faster,” Abate added. “The net result of these actions has been to concentrate more electricity in a diminishing space. So far that has produced small, faster, cheaper chips. But at a certain point, heat and other forms of interference could disrupt the inner workings of silicon chips.”

According to Bao, developers need a material that will enable them to build smaller, faster transistors that use less power to function – and that’s where graphene comes in. The new substance has the physical and electrical properties that will enable it to be used to create next-gen semiconductors, provided a way can be found to mass-produce it.

The Stanford researchers believe that ribbons of the single-atom-thick substance could create semiconductor circuits if they are laid side-by-side. Due to graphene’s minute dimensions and favorable electrical properties, they assert that these nano-ribbons would be able to create chips that are extremely fast but require little power to operate.

“However, as one might imagine, making something that is only one atom thick and 20 to 50 atoms wide is a significant challenge,” said co-author and post-doctoral fellow Anatoliy Sokolov. To overcome that hurdle, the researchers came up with the idea of using DNA as an assembly mechanism, Abate added.

DNA strands are long and thin, and share roughly the same dimensions as the graphene ribbons that Bao and her associates intended to create. They also contain carbon atoms, which just so happens to be the material used to craft graphene. Using both those physical and chemical advantages, the researchers took a small sample of silicon to serve as a support for their experimental transistors.

“They dipped the silicon platter into a solution of DNA derived from bacteria and used a known technique to comb the DNA strands into relatively straight lines,” Abate said. “Next, the DNA on the platter was exposed to a copper salt solution. The chemical properties of the solution allowed the copper ions to be absorbed into the DNA.”

After that, the platter was heated and engulfed in methane gas, which also contains carbon atoms. The heat wound up serving as a catalyst that assisted the assembly process, freeing some of those carbon atoms in the DNA and methane. Once free, those atoms rapidly connected with one another to form stable graphene honeycombs.

“We demonstrated for the first time that you can use DNA to grow narrow ribbons and then make working transistors,” Sokolov said. Bao added that the process required a lot of refinement, but that it could potentially be a step forward in making graphene-based semiconductors a reality. Their research was supported by the National Science Foundation and the Stanford Global Climate and Energy Program.

Read more: Artificial photosynthesis hits milestone in producing cheap, clean hydrogen from water


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