IBM has raised the stakes in the graphene arms race, by creating a complete integrated circuit out of the remarkable form of carbon.
On Friday, the company announced its researchers have used wafer-thin graphene to build a broadband frequency mixer circuit. This near-ubiquitous circuit handles many tasks — translating a radio signal into an audible voice on a mobile phone, for example. The researchers demonstrated the circuit at up to 10GHz, and showed this level of performance was stable at up to 127°C.
In April, IBM unveiled a graphene transistor that it recorded running at 155GHz. This was an increase of more than 50 percent on the previous year's 100GHz effort, and outperforms by far anything silicon can do.
"Designed for wireless communications, this graphene-based analogue integrated circuit could improve today's wireless devices and points to the potential for a new set of applications," IBM said in a statement.
"At today's conventional frequencies, cell phone and transceiver signals could be improved, potentially allowing phones to work where they can't today, while, at much higher frequencies, military and medical personnel could see concealed weapons or conduct medical imaging without the same radiation dangers of X-rays," the company added.
Graphene, a two-dimensional form of carbon, was first isolated less than a decade ago. Its characteristics turned the future of electronics on its head: its strength, thermal, optical and electrical properties are unique, and could lead to smaller, faster and less energy-hungry electronic components. The thermal stability alone means circuits can be kept simple, with no need for a complicated design to compensate for problems caused by heating.
However, graphene can be tricky to work with. In a paper published on Thursday in Science (PDF), the researchers explained that the major challenge in integrating graphene in circuits was getting it to adhere to the other metals and oxides — such as gold — involved in building a chip. So they took a new approach and grew the graphene directly onto a silicon-carbide wafer.
The researchers annealed silicon-carbide wafers, forming layers of graphene on the surface. Making the circuits involved "four layers of metal and two layers of oxide to form top-gated graphene transistor, on-chip inductors and interconnects", IBM said.
In an interview with IEEE, Keith Jenkins, one of the scientists involved with the work, said graphene is also easily damaged by the standard etching process used in creating circuits. To deal with this, the researchers coated the graphene with a polymer called PMMA, which protected the graphene they needed for the circuit.
The method will work with existing optical lithography, IBM said, and can be applied to graphene films created by chemical vapour deposition. This means existing fabs would not need massive revamping to start using graphene in earnest.
Jenkins told the IEEE the 10GHz speed recorded for the newly announced circuit is not the limit, saying that the design is merely a proof of concept. "Ultimately, we should be able to go a lot faster," he said.