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Light-Emitting Particles Yield Faster Computing
schliz writes to tell us that researchers at the University of California San Diego are developing new transistors based on particles called 'excitons' in an attempt to speed up the interaction between computing and communications signals. "Excitons are formed by linking a negatively-charged electron with a positively-charged 'hole'. An exciton decays when the electron and hole combine, emitting a flash of light in the process. By joining exciton-based transistors to form several types of switches, the UCSD physicists were able to achieve switching times on the order of 200 picoseconds."
Excitons...hmmm, what a bright idea!
McCain/Palin '08. Now THAT's hope and change!
wow what if there was a light emmitting particle used in computing....maybe with charge =-e, and spin 1/2...hey that might work great in silicon!
We're talking about a faster porn delivery system. This quote kind of says it all,
""Excitons are formed by linking a negatively-charged electron with a positively-charged 'hole'."
Hmmm.... 200 ps switch times.
A modern processor operating at 2GHz has one clock cycle every 500ps. A signal leaving a flop and travelling to another flop typically goes through about 20 gate delays, yielding a switch time of 500/20=25ps.
Tell me again how this is faster?
Because the one in the submission was fairly content free. You can come to your own conclusions about what its unattributed original source is.
Exciton-based circuits eliminate a 'speed trap' between computing and communication signals
A wikipedia article, but still better than the submission
I'm still scratching my head, but at least it's not drawing blood anymore.
How does a "hole" differ from a positron? In fact, that was Dirac's initial model for a positron -- a hole in a sea of negative energy level electrons.
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
An exiton is just an electron "bounced" out of its location, leaving a positively charged hole behind. The negative electron and the positive hole (the imaginary particle) pair forms an "exotic atom" state similar to a hydrogne atom, but with a much lower binding energy and a much larger size.
This behavior is the standard behavior semiconductors.
It appears the difference here is that when the electron/hole pair reunites, a photon is emitted.
This appear awfully close to what an LED is, and the article is void of any information to distinguish this component from the LED.
don't cut it off www.mgmbill.org
Disclaimer: I work in a lab that develops both transistors and photocells. I don't know exactly what they did, but based on the summary and the article, I'd surmise the following.
In an organic photocell an incoming photo will excite an electron. The positive and negative charges (electron and hole) will be "linked" together (i.e. they will move around together). In this state they are not useful. However, if you can separate them and draw them in different directions, then you'll get a current. They can only be drawn apart if you create a situation in which it is energetically favorable for them to separate, usually by attracting them to high and low work function contacts. Therefore, in a photocell of this type, you sandwich two materials together - one in which it is easy for holes to move, but difficult for electrons, and one in which it is easy for electrons to move, but difficult for holes (called the hole transport and electron transport layers). Then, you put a bias across the layers by using two dissimilar contact materials, one high work function and one low work function. Note that one contact needs to be transparent (ITO is most common) so photons can get to the middle layers.
Anyway, when an exciton is created it goes on a random walk through the material in which it is created, and will eventually collapse. The 'exciton diffusion length' is the distance over which your average exciton will move before collapsing. You want any created excitons to be within a diffusion length of the interface between the hole and electron transport layers. When the exciton hits an interface, it separates and the charges move towards their respective contacts. Put a load across the contacts, and you've got a working circuit (assuming excitons are being created).
This is a mildly simplified explanation, but it works.
Anyway, you can go the other way - imagine injecting an electron in one side and a hole into the other. You could choose your materials such that they would meet up at the interface and collapse together, emitting a photon. This is an OLED, and is conceptually similar to the photocells I just described.
So now imagine that you make it so that either the hole or electron transport layer is semiconducting. You could set up your device such that a dielectric layer and then a 'gate' contact are touching the transport layers along an axis perpendicular to the nominal current flow through your device (like in a thin-film transistor). Then, the layers would only transport charge (like in a transistor) and hence emit light (like in an OLED) when a voltage is applied to the gate contact. Then you have a thin-film device across which you put a bias that only emits light (and draws current) when it is switched 'on' by the gate contact.
In other words, you've combined a TFT with an OLED. Very, very slick.
Excitons are _not_ supposed to be faster switchers (it even says this in the article).
The value proposition is that they can switch at the same rate as electronic circuits, but where normal electronic circuits have slower interconnect, excitons based switching transistors can use faster interconnect.
Basically electrons traveling down wires travel only about 50-75% the speed of light (as I recall that's some phonon-limit). In addition, there with current MOSTFET transistor technology, the gates are voltage sensitive so you need to charge up the capacitance as well. If a exiton transitor emits a photons, the photon has the potential to travel faster (given the right interconnect medium up to near the speed of light) to the next switch resulting in overall faster computing.
In the short term, this could make some things easier transiting things from one chip to another chip (say a processor to a memory chip), between chips in a multi-chip module (using some inter-die optical interconnect layer), or even from one side of a chip to another (which takes longer than a clock cycle in todays advanced high-speed chips).
In the longer term, these types of breakthroughs may actually make computing faster. For example, if your computation involved no feedback, in principle, it would be limited by switching speed (and many circuit design techniques try to do this today by pipelining clocks with data in the same direction), but with feedback, you eventually become limited by circuit-to-circuit propagation delay (so-called wire-delay). This is probably what they are thinking about it helping, but that type of development is probably much further away.
My guitar amp works on vacuum tubes. Basically, the negatively charged cathode emits electrons when heated, creating a "space charge" in the area. In the recto tube (responsible for the characteristic "Sag" effect due to reaction delays when current demand jumps) this floats across to the positively charged anode and gets siphoned away; in a triode or beam tetrode or pentode or whatever else, a grid manages the flow.
I've used a MOSFET as a source follower, the source being the negative source of course, to supply current flow to the Baxandall tone stack. Basically, the MOSFET has a positively doped channel, and a negatively doped source and drain. The source and drain contain many electrons, while the channel contains holes. Applying a charge to the grid causes P material to form an N channel allowing electron flow. In a P channel MOSFET this works the other way. (it's hard for me to explain this, the above is likely wrong)
In a BJT, an NPN has two negative electron-filled materials and a P material filled with holes. A PNP has two areas of holes, and one of electrons.
A silicon diode uses a region full of electrons (anode), and a region full of holes (cathode).
Guess what? Everything works on electrons and holes (holes don't move)!
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How is that new?
Individual electrons travel at much slower speeds in a wire, on the order of molecules in a gas between collisions.
Electrons and positrons aren't made of quarks. They're fundamental particles.
You're right! My bad. I was under the impression that all of the "classic" atomic particles (protons, neutrons, and electrons) were made of quarks.
When our name is on the back of your car, we're behind you all the way!
Basically this means a faster internet, yes?
because if this method can be used to convert photons into electrons quicker it means there will be less internet bottle necks because the backbone is fibre but is controlled by electronic computers
null
How will it perform within a Beowulf cluster?
That's not very fast, actually.
1/200e-9 is only 5GHz. And that's a single transistor, not a processor. 200GHz+ for a single transistor is possible with current transistor processes.
More importantly, how does this help power dissipation? This is our primary concern. If they can run at 5GHz with extremely little power, then it might be useful.
You are looking for this link:
http://en.wikipedia.org/wiki/Velocity_of_propagation
Electromagnetic waves travel at the speed of light in a vacuum. In copper wire it can be as low as 40% of the speed of light.
If I recall, converting from electricity to light and back was really slow, so this will help switching speeds, and thus internet bandwidth.
Electrons themselves do move at an appreciable fraction of the speed of light, but in random directions. The net movement of electrons (called the drift speed) is quite slow, however.