University of Albany Professor Fatemeh Shahedipour-Sandvik and Neeraj Tripathi have eliminated the need for an external electric field to control the electrical properties of graphene. This is achieved by bandgap engineering at the interface between the graphene layer(s) and the underlying substrate. Independent internal control of the electrical properties of graphene layer(s) will allow improvement in performance of a wide range of graphene based devices including sensors and field effect transistors (FETs). The technology is available for licensing.
Graphene is a close cousin of carbon nanotubes, which are in effect graphene rolled up. A nano graphene platelet (NGP) is a nanoscale platelet composed of one or more layers of graphene plane (with a thickness of 0.34 nm to 100 nm). Single-sheet NGPs have demonstrated a much higher thermal conductivity and twice the specific surface areas when compared with single-walled CNTs. NGPs offer potential for greater performance in a wide range of applications and markets including renewable energy, aerospace, automotive, marine, electronics, construction, medical and telecommunications.
Numerous nanotechnology labs and consortia, like the European GRAND (Graphene-based Nanoelectronic Devices) are exploring graphene-based nanoelectronics. Notwithstanding the intense research interest, large scale production of single layer graphene remains a significant challenge.
Recent developments in the growth and characterization of few layers of graphene (monolayer, bilayer and more than 2 layers) have demonstrated immense potential of graphene material to be considered one of the most promising semiconductor materials for the next generation nanoelectronic devices. The unique band structure of graphene layers along with high mechanical and thermal stability has opened a wide range of device applications for graphene thin layers.
An importation characteristic of graphene thin films (monolayer, bilayer) is the fact that their electrical properties can be controlled by applications of an electrical field (perpendicular to the plane of the film). A number of experimental and theoretical reports exist in the literature on controlling electrical characteristics of graphene layers by application of an electric field. Such external field can alter concentration of carriers, and their type as well as the bandgap in monolayer and bilayer graphene layers. To create such electrical characteristics changes in graphene layer via application of a voltage (bias) to a control gate metal deposited on top of the graphene layer.
In this configuration, as has been demonstrated both experimentally and through simulations, the graphene bilayer can be used as a field effect transistor (FET) channel material where conductivity of the channel can be reduced to very low values (i.e. OFF state) by application of an external bias (field). This suggests that graphene bilayer, under this device design, can provide depletion mode (Normally ON) FET. Although demonstration of such Normally ON graphene based device is a great step forward, it is not useful for applications requiring or benefiting from Normally OFF operation.
Graphene sheets have one significant disadvantage compared with the silicon used in today’s chips. Although graphene can be switched between different states of electrical conductivity—the basic characteristic of semiconductor transistors—the difference between these states, called the on/off ratio, isn’t very high. That means that unlike silicon, which can be switched off, graphene continues to conduct a lot of electrons even it its “off” state. A chip made of billions of such transistors would waste an enormous amount of energy and therefore be impractical. The University of Albany discovery eliminates this problem.
Another limitation with the present conventional approach is the need to have a control gate metal deposited on the graphene monolayer/bilayer to control its electrical properties. Novel device design that doesn’t need a deposition of gate metal on top of the graphene layers will enable application of this material to sensors for detection of various gaseous or liquid atoms.
The College of Nanoscale Science and Engineering of the University at Albany is the first college in the world dedicated to research, development, education, and deployment in the emerging disciplines of nanoscience, nanoengineering, nanobioscience, and nanoeconomics. With over $5 billion in public and private investments, CNSE's Albany NanoTech Complex has attracted over 250 global corporate partners - and is the most advanced research complex at any university in the world. The University has a wide variety of nanotechnology innovations available for licensing.
