Graphene, a single layer of carbon atoms in a tight hexagonal arrangement, is a highly researched material due to its incredible electronic properties, with theoretical speeds 100 times greater than silicon. But putting the material into a microchip that could outperform current silicon technology has proven difficult.
The answer may lie in new nanoscale systems based on ultrathin layers of materials with exotic properties. Called two-dimensional layered materials, these systems could be important for microelectronics, various types of hypersensitive sensors, catalysis, tissue engineering and energy storage. Researchers at Penn State have applied one such 2D layered material, a combination of graphene and hexagonal boron nitride, to produce improved transistor performance at an industrially relevant scale.
“Other groups have shown that graphene on boron nitride can improve performance two to three times, but not in a way that could be scaled up. For the first time, we have been able to take this material and apply it to make transistors at wafer scale,” says Joshua Robinson, assistant professor of materials science and engineering at Penn State and the corresponding author on a paper reporting their work in the online version of the journal ACS Nano.
In the article, the Penn State team describes a method for integrating a thin layer of graphene only one or two atoms thick, with a second layer of hexagonal boron nitride (hBN) with a thickness of a few atoms up to several hundred atoms. The resulting bilayer material constitutes the next step in creating functional graphene field effect transistors for high frequency electronic and optoelectronic devices.Previous research by other groups has shown that a common material called hexagonal boron nitride (hBN), a synthetic mixture of boron and nitrogen that is used as an industrial lubricant and is found in many cosmetics, is a potential replacement for silicon dioxide and other high-performance dielectrics that have failed to integrate well with graphene. Because boron sits next to carbon on the periodic table, and hexagonal boron nitride has a similar arrangement of atoms as graphene, the two materials match up well electronically. In fact, hBN is often referred to as white graphene. To be of more than academic interest in the lab, however, the hBN-graphene bilayer had to be grown at wafer scale – from around 3 inches (75 mm) to almost 12 inches (300 mm).
Building on their earlier work with epitaxial graphene, which had already increased transistor performance by 2-3 times, this research adds a further 2-3x improvement in performance and shows the strong potential for utilizing graphene in electronics, according to Robinson. In the near future, the Penn State team hopes to demonstrate graphene based integrated circuits and high-performance devices suitable for industrial-scale manufacturing on 100mm wafers.
In addition to Robinson, the co-authors on the ACS Nano article are Michael Bresnehan, Matthew Hollander, Maxwell Wetherington, Michael LaBella, Kathleen Trumbull, Randal Cavalero, and David Snyder, all of Penn State. The work was supported by the Naval Surface Warfare Center Crane, and instrumentation support was provided by the National Nanotechnology Infrastructure Network at Penn State. “Integration of Hexagonal Boron Nitride with Quasi-freestanding Epitaxial Graphene: Toward Wafer-Scale High-Performance Devices” was published in online in the April 28, 2012, ASAP (as soon as publishable) edition of ACS Nano. Contact Joshua Robinson at email@example.com.
Joshua Robinson | Newswise Science News
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