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High-Performance Monolithic Graphene Transistors Created 99

Posted by samzenpus
from the fresh-out-of-the-lab dept.
MrSeb writes "Hardly a day goes by without a top-level research group announcing some kind of graphene-related breakthrough, but this one's a biggy: Researchers at the University of Erlangen-Nuremberg, Germany have created high-performance monolithic graphene transistors using a simple lithographic etching process. This could be the missing step that finally paves the way to post-silicon electronics. In theory, according to early demos from the likes of IBM and UCLA, graphene transistors should be capable of switching at speeds between 100GHz and a few terahertz. The problem is, graphene doesn't have a bandgap — it isn't a natural semiconductor, like silicon — and so it is proving very hard to build transistors out of the stuff. Until now! The researchers say that current performance "corresponds well with textbook predictions for the cutoff frequency of a metal-semiconductor field-effect transistor," but they also point out that very simple changes could increase performance 'by a factor of ~30.'"
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High-Performance Monolithic Graphene Transistors Created

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  • Hype ? (Score:4, Insightful)

    by Taco Cowboy (5327) on Thursday July 19, 2012 @05:36AM (#40695779) Journal

    ... they also point out that very simple changes could increase performance 'by a factor of ~30

     
    Excuse me but I begin to sense hype
     

    • by nedlohs (1335013)

      Why? Sounds like bog standard scientific research/publishing to me.

      Scientist A: If we did X we would probably get a factor of 30 performance boost.
      Scientist B: Great, but first publish what we have, that way we get 2 publications out of it.
      Scientist A: Better put it in the "future work" in case someone else beats is to it.

      Of course actually checking the paper indicates that isn't actually the case, and it is a much more specific claim than that sentence indicates:

      As the device is a unipolar field-effect tra

    • by subnomine (849148)

      I do feel hyped. I wish there wasn't an article every week promising new wonders that if they ever come to pass I've long forgotten about them. I love it when technology simply comes to market and POW, suddenly we all have megapixel cameras on our cell phones... The industry didn't blah-blah about that for years.

    • Why would you say that?

      Until now!

      But wait there's more!

      very simple changes could increase performance 'by a factor of ~30

      And if you order now, we'll throw in this FREE graphene infused chamois!
      Wash and wax your car with one wipe, and when you squeeze out the water: unicorn tears!

  • by nosh (213252) on Thursday July 19, 2012 @05:41AM (#40695799)

    Just because graphene might became useable does not mean it will replace silicon.

    Silicon has quite some head start, so might survive the alternatives quite some time even in those use cases where alternatives are bette (just like it happened with spinning hard discs as storage medium, or explosion engines for cars).

    And likely it has quite some downsizes that make it unfit for many purposes where silicon shines. Have they for example solved the problem of graphene to always need some current? Being able to build ultra-fast chips is nice, but if there is no way to reduce power usage of parts currently usused that might make it unfit for all but nieche markets. (Well, high-performance needing nieche markets and gamer's PC most likely).

    • by Chrisq (894406) on Thursday July 19, 2012 @05:47AM (#40695819)

      Just because graphene might became useable does not mean it will replace silicon.

      What about when we run out of sand!

    • by art6217 (757847) on Thursday July 19, 2012 @05:57AM (#40695867)

      they for example solved the problem of graphene to always need some current? Being able to build ultra-fast chips is nice, but if there is no way to reduce power usage of parts currently usused

      Many algorithms are serial. A few thousand terahertz transistors might be just enough for them. And if such an algorithm needs a lot of data, a silicone memory around might be sufficient as well.

      If you have a terahertz transistor, it will very likely find an application in computing, even if it would use 1mW when being idle.

      • Easy use is a fast DSP or AD converter. Also DA converters will benefit. Basically we could make such things cheaper and simpler if transistors were faster. Imagine a sampling period in the Terahertz. Useful things even if they don't end up in x86 architecture.

        • Re: (Score:2, Informative)

          by meta-monkey (321000)
          If you need a terahertz sampling rate, your signal must be in the 500GHz range. Nyquist Sampling Theorem [wikipedia.org]. I don't think we can hear 500GHz sounds so well.
          • Who said anything about audio?

          • by Alioth (221270)

            I can't hear 100MHz sounds so well, but my digital storage oscilloscope can. Sampling isn't just for sound.

            • I'm still looking for a digital oscilloscope that can beat a good analogue one... At the same price that is. Maybe if this sort of transistor takes off, I'll get one...

          • A/D and D/A are used for many applications and signals other than audio. Software radios and image processing come to mind.
          • There are lot of applications for the near-terahertz and terahertz band that have nothing to do with audio but an awful lot of mixing/amplification in receiver front-ends and the intermediate stages. The current components are difficult to build and so far there has been a lot of cut-and-try. It's not my field but I can appreciate the difficulties and expenses involved.

            One thing I do wonder about is how/whether the graphene still acts as a extremely good conductor of heat and how to take advantage of it

    • by Anonymous Coward on Thursday July 19, 2012 @06:03AM (#40695899)

      Have they for example solved the problem of graphene to always need some current?

      They didn't.
      The active semiconductor here is SiC, the graphene is only acting as a plain conductor.
      This is as much a graphene transistor as a MOSFET is a aluminium transistor.

      • You seem to be the only other person that actually read the article and understand it. This is a pure BS marketing transistor.
      • by MattskEE (925706) on Thursday July 19, 2012 @05:20PM (#40704361)

        It's a SiC MESFET with graphene gate. It's interesting in that the SiC is the source of C for the graphene, and they use two different growth methods to form a schottky barrier contact for the gate and an ohmic contact for the source and drain. But that's all the graphene is doing is making contacts. Maybe these are really good contacts, but it will still be limited in performance in terms of the gate length and SiC channel material parameters, which are actually pretty good but it's not a graphene transistor at all.

        These hype articles about Graphene fail to mention that conventional highly scaled CMOS processes have cutoff frequencies in the 100's of GHz already, but that's not a metric that relates well to the clock speed of a large digital chip, although it helps. Other very important factors include how tightly you can pack things, getting low-resistance low-capacitance interconnet, and managing FET to FET variability over millions/billions of transistors. These latter factors have a bigger impact on clock speed than the transistors themselves.

        I haven't read much of the latest on graphene transistors but the last ones I saw didn't come close to state of the art silicon, and their off-state current is very high because of the bandgap issue. You can make a bandgap in various ways such as sandwiching the graphene in various materials or making it into small strips but these tend to reduce the high mobility that made graphene so fascinating. I'm sure we'll see some interesting stuff come out of it but most of the press on graphene is the hype that researchers have to do to get funding.

  • It looks like a SiC MOS transistor, with electrodes (D, G, S) made out of graphene rather than metal or polysilicon. Does it really make that much difference in performance over regular MOS transistors? If so, how much of the performance gain comes from the semiconductor material (SiC vs. Si) and how much from the interconnections? How multiple layers of interconnections are handled, if at all?
  • by Required Snark (1702878) on Thursday July 19, 2012 @05:54AM (#40695855)
    I read the article (I know it's not considered good form here on Slashdot), and there seems to be a discrepancy: this is described as being a graphene transistor, but the gate uses silicon carbide as the semiconductor. So it seems like a better description would be a hybrid graphene/semiconductor transistor. Is this correct?

    If it is a hybrid then what are the limitations and how is it better then current all semiconductor circuits? As far as I know (not very much) there is no reason to build silicon carbide integrated circuits, so why would anyone want to use SIC with graphene? Is this a step to something more useful?

    I'm not trolling, I just want to get a better understanding.

    • by zrbyte (1666979) on Thursday July 19, 2012 @06:04AM (#40695907)

      Exactly the channel is SiC, while the interconnects are graphene. so in this sense it's using graphene, but it's not a transistor which uses graphene as the channel material. Previous work that has been cited in the Extremetech article is a graphene channel transistor. So there's a bit of a mix up.
      It is a significant step, but this is in no way revolutionary as the summary implies. Revolutionary would be to induce a band gap in graphene, while keeping it's extremely high mobility for fast switching and using that as the channel material.

      • Do you (or anyone here) know about the power consumption when the transistor switches and how it compares to a silicon transistor? Today on silicon the frequency is often limited by power consumption / thermal considerations. In other words, we know how to go faster on silicon but we don't. If graphene is faster but not more power efficient, then it could limit it's use to the few applications where power / thermal are not a constraint. If it's more efficient, but not much, that could also limit the speed g
        • by zrbyte (1666979) on Thursday July 19, 2012 @07:19AM (#40696195)

          Firstly, why is graphene "faster". This is mainly due to the large mobility [wikipedia.org] of electrons and holes in the material. Furthermore, (I'm not sure here) the fact that the channel is only 1 atom thick, means that switching the transistor from one state to the other should be very fast [nature.com].
          With graphene, the problem is the lack of a band gap. This means that there is always a current flowing through the device no matter which state it's in (on or off, corresponding to 1 or 0). This is a major drawback if you want to make digital transistors out of them, because the device will always draw power no matter what. Ideally you would want the device to have zero or close to zero current flowing through it in one state and have current flow in the other state. So in order to make a power efficient "digital" transistor from graphene you would need to somehow induce a band gap in the material. There are various ways to do this but none have provided the "breakthrough" the summary mentions.
          In some cases graphene transistors could be used, for example analog devices, where the above mentioned issues are not problems. This is the case of the 100 GHz transistors that the article mentions.
          The issue of dissipating heat should be quite different in the case of graphene, because of the materials very good heat transport properties.

          • In some cases graphene transistors could be used, for example analog devices, where the above mentioned issues are not problems.

            Analog circuitry in ICs require a "bandgap reference" (literally) to control bias current. Some smart engineer could provide a work-around, but it's a huge barrier.

          • Re: (Score:3, Informative)

            by Alioth (221270)

            Actually what you want is for zero current to be flowing in one state, and zero current to be flowing in the other state, too. That's the idea behind CMOS, which apart from leakage current, current only ever flows* during the transistion from one state to the other (because while it's transitioning, both N and P channel transistors will be conducting to some degree).

            * (Current may well flow in the quiescent state, if the device is being used as a switch for something through which current flows, such as an

        • by jkflying (2190798)

          The consumption from the switching is due to the capacitance at the gate. This is why smaller transistors are better, smaller transistors --> smaller gate --> smaller capacitance --> less switching power. Lower voltages mean the same thing, since you can use a weaker dielectric without it breaking down and thus lower the capacitance further (eg in DRAM), thereby lowering power consumption.

          How about graphene? It is an extremely good conductor, and that is all, in essence making no difference at all.

        • by nbsr (2343058)

          To answer that we'd first need a working graphene transistor, and the one described in the TFA is not.

          The issue currently limiting performance/watt is transistor transconductance (gain), which for bipolar transistors (at room temperature) is 1decade of output current per 60mV of input voltage change, for MOS (in subthreshold) 1decade/(80~120mV) and significantly less in saturation modes. Considering that you need ~5 decades to get ON/OFF behavior that sets the supply voltage at min. 0.5V, in practice twi

    • by sheepe2004 (1029824) on Thursday July 19, 2012 @06:38AM (#40696033) Homepage

      I read the article (I know it's not considered good form here on Slashdot), and there seems to be a discrepancy: this is described as being a graphene transistor, but the gate uses silicon carbide as the semiconductor. So it seems like a better description would be a hybrid graphene/semiconductor transistor. Is this correct?

      If it is a hybrid then what are the limitations and how is it better then current all semiconductor circuits? As far as I know (not very much) there is no reason to build silicon carbide integrated circuits, so why would anyone want to use SIC with graphene? Is this a step to something more useful?

      I'm not trolling, I just want to get a better understanding.

      Yes. They have only used graphene for the gates and contacts, not the channel itself, so a hybrid graphene/SiC transistor would probably be a better description.

      As for advantages over existing technology: as far as I know the switching speed is dependent on the channel material, NOT the gate etc. So these transistors will (afaik) be no faster than a normal SiC transistor. All the hyperbole about graphene transistors being is only in the linked news article and not in the paper. In fact the final conclusion of the paper is:

      The concept's particular strength, however, lies in the following property: within the same processing steps, many epitaxial graphene transistors can be connected by graphene strip lines along with graphene resistors and graphene/SiC Schottky diodes, and therefore complex circuits can be built up. As a special feature of graphene in contrast to semiconductors, we anticipate that even a complete logic is feasible.

      On the other hand this is still interesting for other reasons:
      1) They have demonstrated large scale integration of graphene. If we can get a bandgap in graphene without sacrificing too much mobility then combined with this kind of work we have a complete graphene chip.
      2) Another thing they emphasise in the paper is the simplicity of the lithography process. Simpler lithography means it's easier to go smaller. Smaller features = better chips.

      TL;DR - the news article is bullshit, the real result is interesting but not revolutionary (yet).

  • by Anonymous Coward

    Immediately it came to mind the image of the large black monolith in Artur C. Clarke's "2001" novel series...

  • by Anonymous Coward
    ".... it isn't a natural semiconductor, like silicon ..."

    Silicon, in its pure state, is an insulator. It only becomes a semiconductor when imputities are added to it.
  • Windows will finally run at acceptable speed?

    • No, Microsoft will see the increased speed as a chance to add even more bloat to it's operating systems, essentially negating any clock speed increases.
    • Windows will finally run at acceptable speed?

      Unfortunately, this will happen in the Year of the Linux Desktop so we will not be able to notice.... :-p

      Interpret that as you like.

  • by Anonymous Coward on Thursday July 19, 2012 @08:46AM (#40696793)

    http://www.nature.com/ncomms/journal/v3/n7/full/ncomms1955.html

    It's open access (free).

    Why the hell does this get linked to "extreme tech" instead of the realFA?

  • Black rectangular with relative dimensions 1:4:9

  • For those of us who "want to believe" this creates some dissonance. It has been widely believed by the observant, that following the crash in Roswell, we "invented" t he germanium diode a few years later. The believers associate the two events as causal. That is we reverse-engineered semi-conductor technology from them. This idea has been supported by some people in the "industry" that the crash was not cleaned up (allegedly by high-up grays or even reptilians) so that we could have a chance to boost our t

    • by Alioth (221270)

      For those not in the know, a transistor is two diodes attached in opposite orientations

      Bipolar transistors look like that, field effect transistors...well, not so much.

  • by Anonymous Coward

    As I recall, silicene (the silicon version of graphene) does have a band-gap and is actively under development for tranisistor use. Techniques such as those in the article may benefit both camps.

  • Since when was silicon a natural semiconductor? Silicon has to be doped before it will act like a semiconductor. If you apply power to a lump of pure silicon, nothing happens. It ignores you. The problem has been finding dopants that work in graphene, not that silicon is inherently semiconducting.

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