Graphene - Moore's Law marches on...

Discussion in 'Electronic Design' started by Dirk Bruere at NeoPax, Jan 7, 2011.


    ( -- Move over silicon. There's a new electronic material in
    town, and it goes fast. That material, the focus of the 2010 Nobel Prize
    in physics, is graphene -- a fancy name for extremely thin layers of
    ordinary carbon atoms arranged in a "chicken-wire" lattice. These
    layers, sometimes just a single atom thick, conduct electricity with
    virtually no resistance, very little heat generation -- and less power
    consumption than silicon.

    With silicon device fabrication approaching its physical limits, many
    researchers believe graphene can provide a new platform material that
    would allow the semiconductor industry to continue its march toward
    ever-smaller and faster electronic devices -- progress described in
    Moore's Law. Though graphene will likely never replace silicon for
    everyday electronic applications, it could take over as the material of
    choice for high-performance devices.

    And graphene could ultimately spawn a new generation of devices designed
    to take advantage of its unique properties.

    Since 2001, Georgia Tech has become a world leader in developing
    epitaxial graphene, a specific type of graphene that can be grown on
    large wafers and patterned for use in electronics manufacturing. In a
    recent paper published in the journal Nature Nanotechnology, Georgia
    Tech researchers reported fabricating an array of 10,000 top-gated
    transistors on a 0.24 square centimeter chip, an achievement believed to
    be the highest density reported so far in graphene devices.

    In creating that array, they also demonstrated a clever new approach for
    growing complex graphene patterns on templates etched into silicon
    carbide. The new technique offered the solution to one of the most
    difficult issues that had been facing graphene electronics.

    "This is a significant step toward electronics manufacturing with
    graphene," said Walt de Heer, a professor in Georgia Tech's School of
    Physics who pioneered the development of graphene for high-performance
    electronics. "This is another step showing that our method of working
    with epitaxial graphene grown on silicon carbide is the right approach
    and the one that will probably be used for making graphene electronics."

    Unrolled Carbon Nanotubes

    For de Heer, the story of graphene begins with carbon nanotubes, tiny
    cylindrical structures considered miraculous when they first began to be
    studied by scientists in 1991. De Heer was among the researchers excited
    about the properties of nanotubes, whose unique arrangement of carbon
    atoms gave them physical and electronic properties that scientists
    believed could be the foundation for a new generation of electronic devices.

    Carbon nanotubes still have attractive properties, but the ability to
    grow them consistently -- and to incorporate them in high-volume
    electronics applications -- has so far eluded researchers. De Heer
    realized before others that carbon nanotubes would probably never be
    used for high-volume electronic devices.

    But he also realized that the key to the attractive electronic
    properties of the nanotubes was the lattice created by the carbon atoms.
    Why not simply grow that lattice on a flat surface, and use fabrication
    techniques proven in the microelectronics industry to create devices in
    much the same way as silicon integrated circuits?

    By heating silicon carbide -- a widely-used electronic material -- de
    Heer and his colleagues were able to drive silicon atoms from the
    surface, leaving just the carbon lattice in thin layers of graphene
    large enough to grow the kinds of electronic devices familiar to a
    generation of electronics designers.

    That process was the basis for a patent filed in 2003, and for initial
    research support from chip-maker Intel. Since then, de Heer's group has
    published dozens of papers and helped spawn other research groups also
    using epitaxial graphene for electronic devices. Though scientists are
    still learning about the material, companies such as IBM have launched
    research programs based on epitaxial graphene, and agencies such as the
    National Science Foundation (NSF) and Defense Advanced Research Projects
    Agency (DARPA) have invested in developing the material for future
    electronics applications.

    Georgia Tech's work on developing epitaxial graphene for manufacturing
    electronic devices was recognized in the background paper produced by
    the Royal Swedish Academy of Sciences as part of the Nobel Prize

    The race to find commercial applications for graphene is intense, with
    researchers from the United States, Europe, Japan and Singapore engaged
    in well-funded efforts. Since awarding of the Nobel to a group from the
    United Kingdom, the flood of news releases about graphene developments
    has grown.

    "Our epitaxial graphene is now used around the world by many research
    laboratories," de Heer noted. "We are probably at the stage where
    silicon was in the 1950s. This is the beginning of something that is
    going to be very large and important."

    Silicon "Running Out of Gas"

    A new electronics material is needed because silicon is running out of
    miniaturization room.

    "Primarily, we've gotten the speed increases from silicon by continually
    shrinking feature sizes and improving interconnect technology," said
    Dennis Hess, director of the National Science Foundation-sponsored
    Materials Research Science and Engineering Center (MRSEC) established at
    Georgia Tech to study future electronic materials, starting with
    epitaxial graphene. "We are at the point where in less than 10 years, we
    won't be able to shrink feature sizes any farther because of the physics
    of the device operation. That means we will either have to change the
    type of device we make, or change the electronic material we use."

    It's a matter of physics. At the very small size scales needed to create
    ever more dense device arrays, silicon generates too much resistance to
    electron flow, creating more heat than can be dissipated and consuming
    too much power.

    Graphene has no such restrictions, and in fact, can provide electron
    mobility as much as 100 times better than silicon. De Heer believes his
    group has developed the roadmap for the future of high-performance
    electronics -- and that it is paved with epitaxial graphene.

    "We have basically developed a whole scheme for making electronics out
    of graphene," he said. "We have set down what we believe will be the
    ground rules for how that will work, and we have the key patents in place."

    Silicon, of course, has matured over many generations through constant
    research and improvement. De Heer and Hess agree that silicon will
    always be around, useful for low-cost consumer products such as iPods,
    toasters, personal computers and the like.

    De Heer expects graphene to find its niche doing things that couldn't
    otherwise be done.

    "We're not trying to do something cheaper or better; we're going to do
    things that can't be done at all with silicon," he said. "Making
    electronic devices as small as a molecule, for instance, cannot be done
    with silicon, but in principle could be done with graphene. The key
    question is how to extend Moore's Law in a post-CMOS world."

    Unlike the carbon nanotubes he studied in the 1990s, de Heer sees no
    major problems ahead for the development of epitaxial graphene.

    "That graphene is going to be a major player in the electronics of the
    future is no longer in doubt," he said. "We don't see any real
    roadblocks ahead. There are no flashing red lights or other signs that
    seem to say that this won't work. All of the issues we see relate to
    improving technical issues, and we know how to do that."

    Making the Best Graphene

    Since beginning the exploration of graphene in 2001, de Heer and his
    research team have made continuous improvements in the quality of the
    material they produce, and those improvements have allowed them to
    demonstrate a number of physical properties -- such as the Quantum Hall
    Effect -- that verify the unique properties of the material.

    "The properties that we see in our epitaxial graphene are similar to
    what we have calculated for an ideal theoretical sheet of graphene
    suspended in the air," said Claire Berger, a research scientist in the
    Georgia Tech School of Physics who also has a faculty appointment at the
    Centre National de la Recherche Scientifique in France. "We see these
    properties in the electron transport and we see these properties in all
    kinds of spectroscopy. Everything that is supposed to be occurring in a
    single sheet of graphene we are seeing in our systems."

    Key to the material's future, of course, is the ability to make
    electronic devices that work consistently. The researchers believe they
    have almost reached that point.

    "All of the properties that epitaxial graphene needs to make it viable
    for electronic devices have been proven in this material," said Ed
    Conrad, a professor in Georgia Tech's School of Physics who is also a
    MRSEC member. "We have shown that we can make macroscopic amounts of
    this material, and with the devices that are scalable, we have the
    groundwork that could really make graphene take off."

    Reaching higher and higher device density is also important, along with
    the ability to control the number of layers of graphene produced. The
    group has demonstrated that in their multilayer graphene, each layer
    retains the desired properties.

    "Multilayer graphene has different stacking than graphite, the material
    found in pencils," Conrad noted. "In graphite, every layer is rotated 60
    degrees and that's the only way that nature can do it. When we grow
    graphene on silicon carbide, the layers are rotated 30 degrees. When
    that happens, the symmetry of the system changes to make the material
    behave the way we want it to."

    Epitaxial Versus Exfoliated

    Much of the world's graphene research -- including work leading to the
    Nobel -- involved the study of exfoliated graphene: layers of the
    material removed from a block of graphite, originally with tape. While
    that technique produces high-quality graphene, it's not clear how that
    could be scaled up for industrial production.

    While agreeing that the exfoliated material has produced useful
    information about graphene properties, de Heer dismisses it as "a
    science project" unlikely to have industrial electronics application.

    "Electronics companies are not interested in graphene flakes," he said.
    "They need industrial graphene, a material that can be scaled up for
    high-volume manufacturing. Industry is now getting more and more
    interested in what we are doing."

    De Heer says Georgia Tech's place in the new graphene world is to focus
    on electronic applications.

    "We are not really trying to compete with these other groups," he said.
    "We are really trying to create a practical electronic material. To do
    that, we will have to do many things right, including fabricating a
    scalable material that can be made as large as a wafer. It will have to
    be uniform and able to be processed using industrial methods."

    Resolving Technical Issues

    Among the significant technical issues facing graphene devices has been
    electron scattering that occurs at the boundaries of nanoribbons. If the
    edges aren't perfectly smooth -- as usually happens when the material is
    cut with electron beams -- the roughness bounces electrons around,
    creating resistance and interference.

    To address that problem, de Heer and his team recently developed a new
    "templated growth" technique for fabricating nanometer-scale graphene
    devices. The technique involves etching patterns into the silicon
    carbide surfaces on which epitaxial graphene is grown. The patterns
    serve as templates directing the growth of graphene structures, allowing
    the formation of nanoribbons of specific widths without the use of
    e-beams or other destructive cutting techniques. Graphene nanoribbons
    produced with these templates have smooth edges that avoid
    electron-scattering problems.

    "Using this approach, we can make very narrow ribbons of interconnected
    graphene without the rough edges," said de Heer. "Anything that can be
    done to make small structures without having to cut them is going to be
    useful to the development of graphene electronics because if the edges
    are too rough, electrons passing through the ribbons scatter against the
    edges and reduce the desirable properties of graphene."

    In nanometer-scale graphene ribbons, quantum confinement makes the
    material behave as a semiconductor suitable for creation of electronic
    devices. But in ribbons a micron or so wide, the material acts as a
    conductor. Controlling the depth of the silicon carbide template allows
    the researchers to create these different structures simultaneously,
    using the same growth process.

    "The same material can be either a conductor or a semiconductor
    depending on its shape," noted de Heer. "One of the major advantages of
    graphene electronics is to make the device leads and the semiconducting
    ribbons from the same material. That's important to avoid electrical
    resistance that builds up at junctions between different materials."

    After formation of the nanoribbons, the researchers apply a dielectric
    material and metal gate to construct field-effect transistors. While
    successful fabrication of high-quality transistors demonstrates
    graphene's viability as an electronic material, de Heer sees them as
    only the first step in what could be done with the material.

    "When we manage to make devices well on the nanoscale, we can then move
    on to make much smaller and finer structures that will go beyond
    conventional transistors to open up the possibility for more
    sophisticated devices that use electrons more like light than
    particles," he said. "If we can factor quantum mechanical features into
    electronics, that is going to open up a lot of new possibilities."

    Collaborations with Other Groups

    Before engineers can use epitaxial graphene for the next generation of
    electronic devices, they will have to understand its unique properties.
    As part of that process, Georgia Tech researchers are collaborating with
    scientists at the National Institute of Standards and Technology (NIST).
    The collaboration has produced new insights into how electrons behave in

    In a recent paper published in the journal Nature Physics, the Georgia
    Tech-NIST team described for the first time how the orbits of electrons
    are distributed spatially by magnetic fields applied to layers of
    epitaxial graphene. They also found that these electron orbits can
    interact with the substrate on which the graphene is grown, creating
    energy gaps that affect how electron waves move through the multilayer

    "The regular pattern of magnetically-induced energy gaps in the graphene
    surface creates regions where electron transport is not allowed," said
    Phillip N. First, a professor in the Georgia Tech School of Physics and
    MRSEC member. "Electron waves would have to go around these regions,
    requiring new patterns of electron wave interference. Understanding this
    interference would be important for some bi-layer graphene devices that
    have been proposed."

    Earlier NIST collaborations led to improved understanding of graphene
    electron states, and the way in which low temperature and high magnetic
    fields can affect energy levels. The researchers also demonstrated that
    atomic-scale moiré patterns, an interference pattern that appears when
    two or more graphene layers are overlaid, can be used to measure how
    sheets of graphene are stacked.

    In a collaboration with the U.S. Naval Research Laboratory and
    University of Illinois at Urbana-Champaign, a group of Georgia Tech
    professors developed a simple and quick one-step process for creating
    nanowires on graphene oxide.

    "We've shown that by locally heating insulating graphene oxide, both the
    flakes and the epitaxial varieties, with an atomic force microscope tip,
    we can write nanowires with dimensions down to 12 nanometers," said
    Elisa Riedo, an associate professor in the Georgia Tech School of
    Physics and a MRSEC member. "And we can tune their electronic properties
    to be up to four orders of magnitude more conductive."

    A New Industrial Revolution?

    Though graphene can be grown and fabricated using processes similar to
    those of silicon, it is not easily compatible with silicon. That means
    companies adopting it will also have to build new fabrication facilities
    -- an expensive investment. Consequently, de Heer believes industry will
    be cautious about moving into a new graphene world.

    "Silicon technology is completely entrenched and well developed," he
    admitted. "We can adopt many of the processes of silicon, but we can't
    easily integrate ourselves into silicon. Because of that, we really need
    a major paradigm shift. But for the massive electronics industry, that
    will not happen easily or gently."

    He draws an analogy to steamships and passenger trains at the dawn of
    the aviation age. At some point, it became apparent that airliners were
    going to replace both ocean liners and trains in providing first-class
    passenger service. Though the cost of air travel was higher, passengers
    were willing to pay a premium for greater speed.

    "We are going to see a coexistence of technologies for a while, and how
    the hybridization of graphene and silicon electronics is going to happen
    remains up in the air," de Heer predicted. "That is going to take
    decades, though in the next ten years we are probably going to see real
    commercial devices that involve graphene."

    Provided by Georgia Institute of Technology (news : web)

    Dirk - My new book - Transcendence UK - Occult Talk Show
    Dirk Bruere at NeoPax, Jan 7, 2011
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  2. Dirk Bruere at NeoPax

    Rich Grise Guest

    Dirk Bruere at NeoPax wrote:
    > ( -- Move over silicon. There's a new electronic material in
    > town, and it goes fast. That material, the focus of the 2010 Nobel Prize
    > in physics, is graphene -- a fancy name for extremely thin layers of
    > ordinary carbon atoms arranged in a "chicken-wire" lattice.

    Isn't this just graphite, sliced really, really thin?

    Rich Grise, Jan 9, 2011
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  3. On 09/01/2011 01:06, Rich Grise wrote:
    > Dirk Bruere at NeoPax wrote:

    >> ( -- Move over silicon. There's a new electronic material in
    >> town, and it goes fast. That material, the focus of the 2010 Nobel Prize
    >> in physics, is graphene -- a fancy name for extremely thin layers of
    >> ordinary carbon atoms arranged in a "chicken-wire" lattice.

    > Isn't this just graphite, sliced really, really thin?

    Really simple.
    Another discovery that was decades late.

    Dirk - My new book - Transcendence UK - Occult Talk Show
    Dirk Bruere at NeoPax, Jan 9, 2011
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