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."
The "100 times greater"... (Score:5, Interesting)
...refers to electron mobility [wikipedia.org], 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!
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...refers to electron mobility [wikipedia.org], 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!
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. :-)
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uuuuh i can feel your nipple neutron there baby!
Re:The "100 times greater"... (Score:5, Interesting)
The increased mobility has little to do with gates. In fact, you want gates (in MOSFETs [wikpedia.org]) 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.
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I'm not sure why it's considered so amazing to discover...
Science writing is frustrating if you know anything at all about what's being discussed. It's dumbed down to the point that you feel less informed for having read it. They invariably leave out the "trivial" little detail that makes it all make sense. They might as well just write, "Something new and nifty and important has been discovered! But it's too complicated to explain it to you, so we'll spare you the boring, complicated details."
Re:The "100 times greater"... (Score:5, Funny)
Your in-depth analysis intrigues me, and I wish to subscribe to your newsletter.
Question about "holes" (Score:3, Interesting)
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, inste
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Representing charge as "holes" is useful for current said to be flowing from a higher voltage (lacking electrons) to a lower voltage. The electrons are actually going from where they are in excess (giving a more negative charge) to where they are lacking. Therefore, the "holes" and electrons are trading places. It's like heat being dissipated, and saying "cold" is moving in.
The way you describe the motion of electrons and holes as being equivalent but in opposite directions is a very good way to look at i
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Mod parent +1 Informative, pls. (Score:2)
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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.
First of all, holes are not the result of net positive charges in an atom. In silicon, you can create holes by replacing a silicon atom in the crystal lattice with a boron atom. Silicon has 4 valence electrons, but boron only has 3. Therefore, the silicon atom that is replaced by the boron could form 4 bonds with neighboring silicon atoms. The boron can only form 3. The remaining empty space is what we call a hole. Note that nothing is electrically charged.
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.
A hole moving in one direction is not the sa
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where the extra dot in the colon shows the extra electron.
Additionally, that extra electron is not forced into the conduction band; some small minority will still be associated with an atom at room temperature. Additionally, the percen
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Re:The "100 times greater"... (Score:5, Funny)
I think you mean silicone.
The "e" is very important. (As the raver said to the priest).
Re:The "100 times greater"... (Score:5, Funny)
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negligable thickness -- (Score:1)
I know, I know, a different enhancement problem set from the target of silicone [wikipedia.org] enhancements. But I prefer the more natural sort of enhancement, myself.
But the health issues of silicone and asbestos and the like do raise a question to me about graphene and other carbon filament materials.
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Polycrystal silicon is used for transistor gates and routing signals over very short distances, maybe they mean to r
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Does "higher electron mobility" necessarily mean more conductive in the "off" state? I thought it just meant faster switching.
I was just pointing out that it doesn't address the significant problems in current devices. I don't think it will significantly affect either if it were used as a replacement semiconductor (if it even could be used that way). When materials like carbon nanotubes are made into 'transistors' the device changes significantly and generally works on different principles that current devices, so what holds for silicon transistors goes out the window.
Re:The "100 times greater"... (Score:5, Interesting)
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.
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No, by that time it will more closely resemble a large truck.
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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.
There also is a group investigating this at Georgia Tech: http://www.physics.gatech.edu/npeg/index.html [gatech.edu] (site has a halfway-decent FAQ for those not familiar with graphene).
I met one of the students from the GT group recently and he mentioned the scotch tape solution and said he said his lab were investigating how to manufacture the material practically. For all it's promise, I got the impression that two or three major breakthroughs were needed to make it viable. It's definitely a few years away. (I me
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Re:The "100 times greater"... (Score:4, Interesting)
Re:The "100 times greater"... (Score:5, Informative)
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Seriously though, thanks, I didn't realize that moving to on-die cache would've made such a drastic difference in transistor count. Very interesting.
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Cache is the easy way out - but it doesn't necessarily give you much better performance beyond a certain size (for typical workloads anyway).
So what do you do if you have so much transistors left, that using all
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I will physically reach out and strangle the first person to make a joke relating 100GHz to the system requirements of Windows...
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But... (Score:2)
Imagine 100Ghz! (Score:1)
Unfortunate name (Score:3, Funny)
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Re:Unfortunate name (Score:4, Funny)
Is it actually possible to Godwin a thread about microprocessor engineering?
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"Herr Fuhrer" is just a title, literally translated as Mr. Leader.... just like we use Mr. President.
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Well... um... who do you suppose that that title is actually most associated with? Hint: Germany's current president does not use that title, or any variation on it.
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Which part of "any variation" was I unclear about? I don't think she uses Frau Fuhrer, either.
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I, for one... (Score:3, Funny)
Seriously, however, I don't expect to see a CPU based on this anytime soon.
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so you shouldn't, at one atom thick.
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The Sony Playstation 36, Holodeck Edition.
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You must be extremely conservative...
I'm waiting for my one MegaCore processor with 1,048,576 cores, while mocking the market-war with MegiCore processors who only have 1,000,000 cores, but perform better at rendering realistic 3D models of females.
Would oxidation be a problem? (Score:5, Interesting)
I recall that early compact discs had this problem, in which oxygen trapped in the plastic would oxidize the aluminum and reduce its reflectivity.
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New material? (Score:1)
At heavy-load CPU temps? (Score:1)
Bad for RF? (Score:2, Informative)
Questions to ask proponents of new semiconductors (Score:4, Insightful)
2) Can you make good low resistance contacts?
3) Can it be doped?
Graphene probably fails 1 and 2 at this point. I'm not sure about 3.
2D (graphene) and 1D (carbon nanotube) semiconductor systems have a lot of trouble with surface effects ruining your ability to make decent devices.
Re:Questions to ask proponents of new semiconducto (Score:2)
Re:Questions to ask proponents of new semiconducto (Score:1)
If electron mobility was important silicon would have been replaced by Galium Arsenide years if not decades ago. GaAs can pass all of the first 3 requirements suggested by the parent - but not in a scalable way. For example you can get a good quality insulator on it, but its just bloody hard to do.
Re:Questions to ask proponents of new semiconducto (Score:1)
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Graphene Valley? (Score:1)
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HFE (Score:1)
link to the paper (Score:3, Informative)
http://www.thinkgene.com/um-physicists-show-electrons-can-travel-over-100-times-faster-in-graphene-than-in-silicon/ [thinkgene.com]
Won't be used commercially for awhile (Score:1)
What I'd like to build with this stuff is ... (Score:2)
... a Yagi antenna [wikipedia.org] resonant at a wavelength somewhere between 700nm and 400nm. Now I just need a high power transmitter and some feedline to connect to it.
But carbon is ee-vul!! We must reduce our graphene (Score:1)
Excellent, I can replace... (Score:2)
Oh boy... (Score:1)
let me clear up some confusion... (Score:5, Informative)
It can be doped. This is another thing Fuhrer has done (as well as other people... but this is his article we're talking about). You don't want to insert something into the crystal structure (that ruins it), but you can layer the top of it with potassium ions (about 1 per 1000 carbons), which dopes it just fine. This isn't a bulk semiconductor though, and the addition of charged impurities (dopants) decreases device performance (in bulk, it's a metal). You can very easily electrostatically gate graphene in any direction you want; transistors and PN junctions are easy to make this way.
It is not hard to make graphene. The "scotch tape" method from Manchester is widely used, but there are a number of other ways to do it which may be commercially viable: oxidizing graphite, ultrasounding graphite with special polymers (Dai's method), growing it from SiC wafers. Of course, none of these really work yet, and may never be economical.
Graphene is stable in air (almost all devices are measured in air at some point), and liquids. It's not going to spontaneously dissolve on you just because it's only 1 atomic layer thick. It's actually very robust.
It can be used with silicon processing techniques. People are using SiO2, HfO2 and all the usual silicon processing with it.
Big companies are looking at this material. IBM has already reported results on their work at physics conferences, I'm fairly sure that the more secretive companies (Intel) are also working with graphene... just like they worked with nanotubes.
Graphene for sale (Score:1)
It is interesting stuff - I saw Prof Geim speak about it and it seems to me one of these areas where quantum theory and experiment intersect,
New? (Score:2)
can you put a billion devices on a chip for $100? (Score:2)
Technical error (Score:2)
Sounds familiar (Score:2)
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Silica : crystalline silicon dioxide aka sand
Silicon : element # 14, greyish semimetallic crystalline
Silicone : Inorg. polymer typ. -Si(CH3)2-O- Liquid or can be rubber if crosslinked. Using for boob jobs.
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