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Hardware Science

Graphene May be the New Silicon 115

esocid writes to share that University of Maryland physicists have demonstrated that the material of the future may be graphene rather than silicon. Electricity conduction through graphene is about 100 times greater than that of silicon and could offer many improvements to things like computer chips and biochemical sensors. "Graphene, a single-atom-thick sheet of graphite, is a new material which combines aspects of semiconductors and metals. [...] A team of researchers led by physics professor Michael S. Fuhrer of the university's Center for Nanophysics and Advanced Materials, and the Maryland NanoCenter said the findings are the first measurement of the effect of thermal vibrations on the conduction of electrons in graphene, and show that thermal vibrations have an extraordinarily small effect on the electrons in graphene."
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Graphene May be the New Silicon

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  • by 26199 ( 577806 ) * on Monday March 24, 2008 @06:34PM (#22850836) Homepage

    ...refers to electron mobility [], a concept I hadn't previously encountered. But it's easy enough to understand: if I apply a unit electric field to a material, how fast does it make the electrons drift? This is the mobility.

    Apparently graphene (also new to me ... a single-atom layer of carbon) is exciting because it has much higher electron mobility than silicon. Which leads to faster switching times, although they don't explain that part.

    All this seems to be theoretical at the moment, due to insufficiently pure graphene. Still, 100th the switching delay is not a bad target to be aiming at... 100Ghz processing!

  • by MichaelCrawford ( 610140 ) on Monday March 24, 2008 @06:47PM (#22850932) Homepage Journal
    While you could coat it with a hard protective layer like aluminum oxide, I think it would be hard to protect it well enough to prevent oxidation from degrading a layer only one atom thick.

    I recall that early compact discs had this problem, in which oxygen trapped in the plastic would oxidize the aluminum and reduce its reflectivity.

  • by wass ( 72082 ) on Monday March 24, 2008 @06:58PM (#22851046)
    Graphene has been studied for a few years now, even longer if you count it as rolled into a nanotube.

    What took awhile (and was solved with a fairly low-tech solution : scotch tape) was how to make a single layer of graphene to measure, whereas graphite usually rolled off into multi-layer pieces.

    Graphene is interesting for a number of reasons. Primarily is it's Minkowski lightcone-like density of states. The Fermi level lies right at the cone vertex, which makes this material a "zero-bandgap insulator", which brings about a huge number of interesting properties in itself.

    Anyway, graphene has been hugely popular in condensed matter physics for a few years now, and people have studied the phonon spectra, I remember going to a seminar about the modes of graphene in a carbon nanotube a few years ago.

    However, don't get your hopes up for mass-produced graphene tech anytime soon. While people will probably demonstrate small-scale single-electron transistors or other interesting graphene devices (if they haven't already), the ability to deposit and pattern graphene is still very crude, and it's hard to do anything other than one-off devices at this point.
  • by DigiShaman ( 671371 ) on Monday March 24, 2008 @07:02PM (#22851074) Homepage
    I remember reading about how physicists are running into the limitations of "C" (speed of light) with regards to signal propagation across the CPU die. Even though something measuring 143 mm^2 is small, at speeds of 100GHz (or was that 1Thz), I doubt your processing can remain symmetrical. If that's true, such fast CPUs will need to be engineered for asymmetrical processing instead.
  • by mapsjanhere ( 1130359 ) on Monday March 24, 2008 @07:31PM (#22851300)
    It's also very hard to "solder" interconnects on a single layer sheet. Alnd, due to the 2 dimensional nature of the graphene sheet you can't easily take advantage of modern multilayer silicone processing. Making a true device from this will be challenging.
  • by Cecil ( 37810 ) on Monday March 24, 2008 @07:39PM (#22851350) Homepage
    On the other side of the coin, the design for an original Pentium had around 5 million transistors. Modern processors have more like 300 million. What's changed? Well, dual-core, and 64-bit, sure. But a lot of those extra transistors are to create extra pipelines or additional specialized instructions or even specialized pipelines that only run specialized instructions to compensate for the fact that the clock speeds just won't ramp up as quickly as designers want. Perhaps if we were able to start cranking up the clock speeds again, it would be possible to start streamlining those pipelines and instruction sets into something more manageable for keeping your signals properly synchronized.
  • by Btarlinian ( 922732 ) <tarlinian@gm a i l . com> on Monday March 24, 2008 @08:10PM (#22851656)

    Thanks, now I don't have to RTFA. I was wondering why pure conductivity improvements are good for gates. Semiconductors are used for a reason. :-)

    The increased mobility has little to do with gates. In fact, you want gates (in MOSFETs []) to be as resistive as possible, but still not attenuate the electric field that results from the gate voltage, hence the use of Halfnium dioixde instead of silicon dioxide (you can make it thicker, (and thus more resistive) while still having a strong enough field.)

    Mobility results from the equation v=(mu)E, where mu is the mobility and v is the velocity of an charge carrier (electron or hole) The reason we use semiconductors is that we can easily control the number of electrons or holes. But by increasing the speed of electrons, we can allow them to switch faster since they will be able to cross the channel more quickly. That's why smaller transistors can switch more quickly, the channel length is shorter so it takes less time for carriers to traverse them.

    I'm not sure why it's considered so amazing to discover that graphene has a good electron mobility. Since, the entire structure consists of delocalized pi orbitals, you would expect electrons to easily travel through graphene. I'm not sure how graphene would be doped either. I suppose you could use boron and phosphorous like in silicon, but it remains to see if they will still bond appropriately. Ah well, there's a reason, they're professors and I'm a student.

  • by GPS Pilot ( 3683 ) on Tuesday March 25, 2008 @12:29AM (#22853578)
    As I understand it, a "hole" is just the absence of an electron, which leads to a net positive charge for a particular atom. Kind of like a positive ion, but I think use of the term "ion" is limited to liquid solutions/gases/plasmas.

    An electron can move and fill a hole, but leaves another hole behind in the location it just departed. So a "hole" moving in one direction is entirely equivalent to an electron moving in the opposite direction, is it not?

    If so, why does this term have any usefulness, if, instead of saying "the hole moved from point A to point B" you could just as easily say "the electron moved from point B to point A"?

    Help me understand why much ado is made about holes.

Order and simplification are the first steps toward mastery of a subject -- the actual enemy is the unknown. -- Thomas Mann