First Graphene Transistor

An anonymous reader writes "UK researchers are announcing the first ever workable transistor made of graphene — that's one layer of carbon atoms. It's thinner and smaller than a silicon transistor can ever be, and it works at room temperature. When silicon electronics are dead, this is what many speculate is going to take over. There's slight controversy as they decided to announce their results via a review article, rather than wait for their (submitted) peer review paper to come out."

Re:practical?

[cyfer2000]

There are two ways to make graphene I have known, one is to exfoliate graphite [wikipedia.org] and the second one is to produce an oversaturated silicon carbide single crystal [sciencemag.org], and the graphene will grow epitaxially from the carbon layer on the surface of the silicon carbide crystal. None of these two can be "practical" IMHO. I also believe the researchers claim the new transistor is "practical" just to differentiate them from the old [gatech.edu] ones [whatsnextnetwork.com]. Anyway I will read the real paper on Nature Materials and see what Novoselov's group has done this time.

Re:Impressive

[PhysicsPhil]

The Intel work you reference is just bonding an indium phosphide laser chip onto a silicon wafer, not actually creating a silicon laser by itself. While a Raman laser has been produced in silicon, the real device of interest, an electrically pumped diode laser is still the stuff of dreams.

Re:What's with the picture in TFA?

[purify0583]

Perfect graphene is flat. But any imperfections caused by a missing carbon or an extra carbon will cause it to bend slightly. Which would explain the ripples.

Source from wikipedia :

Perfect graphenes consist exclusively of hexagonal cells; pentagonal and heptagonal cells constitute defects. If an isolated pentagonal cell is present, then the plane warps into a cone shape; insertion of 12 pentagons would create a fullerene. Likewise, insertion of an isolated heptagon causes the sheet to become saddle-shaped. Controlled addition of pentagons and heptagons would allow a wide variety of shapes to be made.

Re:What's with the picture in TFA?

[PhysicsPhil]

I mean, the article's about a completely flat sheet of atoms joined in a structure with four edges from eac node. So, why are they showing a ripply surface made from a hexagonal structure, with three edges from each node?

As you note in your follow-up post, the hexagonal bonding structure is correct for graphene. The rippling motion is a result of thermal fluctuations. Normally you don't see it much because the graphene is bonded to a substrate, but as the second link in the main article explains, free standing membranes do actually ripple.

Re:practical?

[Chris Burke]

I think background radiation will be one of its main reasons it will fail for a CPU and RAM. With a structure 1 atom thick there is no room for failure. Either an atom exists or it doesn't. Knock an atom out of place then it fails. With a conventional transistor as its bulk material all that happens is it degrades its performance but it can take it (most of the time).

That's true, and actually with current silicon device sizes a single alpha particle strike has the possibility of flipping a bit in an SRAM. This is one part of why NASA uses old cpus -- one of the simplest methods of radiation hardening is to simply use larger structures that require a larger amount of energy to change state. Then they add more shielding and such on top of course.

Peer Review!

[drolli]

Peer Review is a very important thing. Not only it prevents some bad reseaarch from entering Journals, but it actually increases the quality of articles published - because Referees ask meaningful Questions, whcih can help to clarify unclear points.

Re:Works at room temperature?

[Baron Eekman]

Actually, it was Nosovelov and Geim's group in Manchester. See e.g. their original article in Science [sciencemag.org].

Re:practical?

[crgrace]

That's true, and actually with current silicon device sizes a single alpha particle strike has the possibility of flipping a bit in an SRAM. This is one part of why NASA uses old cpus -- one of the simplest methods of radiation hardening is to simply use larger structures that require a larger amount of energy to change state. Then they add more shielding and such on top of course.

That's actually not true at all. The chance a transient error (SRAM bit flip) or worse, a long term change in the threshold voltage of a device actually gets worse when the structures are larger. That is because the chance for a radiation event to occur in the gate oxide is linearly proportional to the thickness of the oxide. Fine-line CMOS has thinner oxides, so it is more tolerant.

On top of that, what you are discussing (shielding, structure geometry) is called radiation tolerance, not radiation hardening. A radiation hard IC process implies dielectric isolation between the devices. For example, the use of SOI is quite prevelent in nuclear/space applications. The reason NASA uses old CPUs is because they are available in rad-hard dielectrially isolated technology. Intersil in Palm Bay, FL, still has rad-hard 286s coming off the line right now. Dielectrically isolated IC processes with the feature sizes needed to produce modern CPUs simply do not exist because of the lack of an economic incentive. That is the only reason NASA and DOD use such old CPUs.

Re:practical?

[Joe Dutch]

In fact that's the beautiful, and arguably the most perplexing, thing abbout graphene. Charge carriers travel thousands of interatomic distances without scattering, even when under 'dirty' conditions. Adsorbates, proximal substrates, lattice vibrations, none of these seems to phase the carriers in their passage from one place to another. This is truly astounding, and we really don't yet know why. But it does suggest that this is one less big thing to worry about when it comes to making devices.

Moreover, graphene is structurally robust, even down to an atom thick and sub-10-nm wide. It doesn't fall apart, it doesn't aggregate, it doesn't oxidize --- it's just happy to be what it is. This is not as astounding as the ballistic nature of it's carriers --- the carbon-carbon bond in graphene/graphite is one of the strongest known, stronger even than the carbon-carbon bond of diamond! Nonetheless, even the most naively optimistic researchers find this pretty amazing.

Of course, there are *lots* of other big things to worry about, it's just that material and electronic stability aren't among them.

As per making a ballistic field-effect transistor (a la a carbon nanotube FET), this has already been done, and the characteristics are rubbish! And there's no way around this. Conventional device structures in graphene leak like sieves, which seems to be fundamental rather than a consequence of fabrication issues. Which is why the SET result is so encouraging. The characteristics are still not fabulous, or at least not yet, but it's likely that this could be the only way to make a transistor with useful ON-OFF behaviour.

Oh, and CNTs are never going to be a goer for consumer electronics, imho. Their properties are just too dependent on their chirality (which determines even whether they are semiconducting or metallic), and there is still no good way of addressing this. Graphene doesn't suffer from this problem, the properties of one sheet are the same as those of any other sheet. Rotational alignment and edge structure could causes problems at the dimensions people are talking about for future single electron devices. But at least you don't have the problem of not knowing if you've even got a metal or a semiconductor, as you do with nanotubes.

But then of course, there are all those unseen issues to come. But that's the wonderful thing about emerging fields of research, you get to wax lyrical about all the great possibilities that could be without all those bothersome reality-induced pitfalls that always arise. We're still in the honeymoon period of graphene research. How long the actual marriage will last is anyone's guess.