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Massachusetts Institute of Technology - Technology Review - How to save the troubled Graphene transistor

DCN Corp® - Graphene-based non-boolean logic circuits.  Credit - University of California, RiversideAs the buzz with all aspects of nanotechnology continues on a daily basis - there still remains the problem of ensuring that Graphene "switches off" when being prompted to act like a conventional semiconductor.  It is the lack of Graphene's switching off mode which threatens to scupper its future use in emerging generation of transistors.  However, researchers from University of California, Riverside - believe they may have found an innovative solution.

Clearly the writing is on the wall for the traditional silicon (Si) chip - at an increasing rate transistors have been shrinking for the last half of century but realistically they cannot be continually miniaturized forever.  Nowadays most industry pundits believe that the down-scaling of the Si chip technology cannot extend much beyond 2026.  Therefore, the million dollar question, is what will replace it?

One heavily speculated possibility is Graphene, whereby various teams around the world have been employing the 'wonder material' to fabricate faster transistors.  For example, last year, one team clocked a Graphene transistor at a cool 427 GHz, so you could be mistaken for assuming that Graphene is the perfect Si replacement.  However, not so fast, because there is a significant problem with Graphene which makes it difficult to employ in conventional transistors.  That problem being that it does not have a band gap.  Meaning that there is no energy range in Graphene in which electron states cannot exist.  In other words - effectively it is impossible to switch off Graphene, which as stated above constitutes a serious trouble for fabricating towards a future nano transistor.

Today (20/08/2013) - Guanxiong Liu and co-workers at Riverside (University of California) - have managed to find a way that enables for Graphene transistors with no band gap to work in an entirely different manner than that of conventional switches.  As stated - "the obtained results present a conceptual change in Graphene research and indicate an alternative route for Graphene's applications in information processing,"

Every known solid material has its own characteristic bands of energy whereby electrons can flow to form a conductor or are prevented from flowing to form an insulator.  In a conventional semiconductor - electrons cannot flow at low energy and so the material behaves as an insulator.  However, a relatively small amount of energy can 'push' electrons into the conduction band where they flow freely forming a conductor.  Essentially the energy difference between such insulting and conducting states is the band gap and so the ability to switch between one state and the other is the definitive characteristic of a transistor/switch.

The problem with Graphene as stated above is that it has no band gap, thus, electrons can freely flow at any energy.  Moving forward - the major focus of Graphene engineers/researchers (worldwide) is to find means of creating an artificial band gap employing methods, such as applying electric fields, doping with atoms or by stretching and squeezing the material.  Unfortunately, such approaches have met with modest success, because practical digital circuits require a band gap on the order of 1 eV at room temperature (RT).  However, the best efforts with Graphene have merely produced a modest band gap in a few hundred meV.  Even such a milestone has come at a serious cost.  The best Graphene transistors are super fast but they heavily 'leak' energy and/or current like there's no tomorrow and/or like water through a sieve.

It is claimed that Liu and co-workers have come-up with a different approach - "we intentionally avoid any attempt to artificially induce an energy band, which would make Graphene "more-silicon-like,"  Instead it is proposed to rely on a different phenomenon dubbed negative resistance to enable for transistor-like behavior.  In essence negative resistance is the counter-intuitive phenomenon in which a current entering a material causes the voltage to drop across the material.  Multiple research groups - including the Riverside one, have shown that Graphene demonstrate negative resistance in certain circumstances.  The Riverside idea is to take a standard Graphene field-effect transistor and find circumstances whereby it demonstrates negative resistance (or negative differential resistance).  Effectively the drop in voltage is assumed to act like a switch to perform as a logic gate.

Again, it is claimed that the main contribution of the published result is to demonstrate how several Graphene field-effect transistors can be combined/manipulated in a way which produces conventional logic gates.  Journal citation available here.  For example - Liu and co-workers can build elementary XOR gates out of only three Graphene field-effect transistors when compared to eight when employing Si.  Such a difference translates to a significantly smaller area on a chip - typically a 1/1000 smaller.  In summary, all such claimed benefits translate into a system which dramatically outperforms Si - Liu and co-workers state "several orders of magnitude higher than for any reported or even projected scaled circuits."  Original article available here

DCN Corp finds that the above research extremely innovative, and as claimed previously - we at DCN Corp believe we have developed a coating methodology enabling for the even fabrication of nanoparticles, which could effectively act as a band gap interface for subsequent fabrication by Graphene.  In being able to do so, and if you and/or your colleagues are interested in making such a coating methodology reality - please ensure to contact the company as soon as practicably possible.