Scientists develop new graphene inverter

Ever since its discovery in 2004, scientists have considered graphene, the form of carbon that makes up graphite, as a possible alternative to the element silicon for use in electrical circuits. However, interest in graphene has largely died down due to the fact that it does not naturally have the traits necessary to allow circuits to store information.

New technology developed at the Birck Nanotechnology Center of Purdue University may have gotten around this problem, finally allowing the use of graphene in circuits. A team of researchers led by Hong-Yan Chen, a doctoral student, has created a new type of graphene inverter that can operate at room temperature. An inverter is a device that changes the type of current running through an electrical circuit to a different type.

Inverters are made up of two different types of transistors, which are electronic devices that amplify or change the direction of current in a circuit. Graphene inverters have been created before, but they could only successfully operate at minus 320 degrees Fahrenheit, making them unusable for all but very specialized uses, such as in cell phones and electronics for military operations.

One of the main problems in trying to replace silicon with graphene is that silicon has impurities added to it to make it usable in inverters. Because of its makeup, the same cannot be easily done to graphene. Researchers have possibly solved this problem by the use of "electrostatic doping," or setting up metal gates near graphene channels and inducing an electric field through them. This concept has existed for some time, but has never been used on graphene before. "It is reported for the first time by our work that electrostatic doping is useful to create digital graphene inverters," said Chen.

Another problem is that graphene has a zero band gap. This prevents it from turning the transistor on and off, which is how circuits save information.  Instead of addressing it directly, Chen and his team got around this problem by using a different type of design, termed a  "smart device layout" by Chen for the inverter. They came up with this design by focusing on the characteristics of an inverter.

Why go through all this trouble? Graphene circuits could one day power our computers and many other types of electronics we use daily. Researchers believe that devices using graphene would be able to operate at very high speeds and could also be cheaper to manufacture. "The next challenge is to show graphene's usefulness in digital applications," Chen states. He believes that the development of graphene inverters could someday lead to the creation of an "all-graphene-circuit," which could be used in digital applications.

The team is now working on perfecting their prototype, while collaborating with other groups who are fixing the problems with the band gap and electrostatic doping. The progress made by these groups will determine how long it takes to produce an all-graphene circuit. "There are several modules of our prototype device that need further work on. Collaborations with research groups working on bandgap opening or graphene doping are needed to shape the graphene inverter into its ultimate form. So the time really depends on the progress in these two fields," Chen explained.

The research paper about this development, entitled "Complementary-Type Graphene Inverters Operating at Room-Temperature," was presented in June 2011 at the 2011 Device Research Conference in Santa Barbara. Hong-Yan Chen and Joerg Appenzeller, who is an electrical and computer engineering professor and the scientific director of nanoelectronics at the center, are the authors of the paper.