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The problem is with carbon in general is it has a band gap 5x larger then Silicon. Which overall (but not entirely) means if you want to build a transistor with
by valarauca1 12y ago
The problem is with carbon in general is it has a band gap 5x larger then Silicon. Which overall (but not entirely) means if you want to build a transistor with Diamond (or graphene) you need to put 5x as much voltage into it.
The reason graphene is great for transistors is with its higher band energy its 5x harder for it to soft set itself. So if we pretend todays 11nm transistors have a 1% chance of electron tunneling, carbon would have a 0.2%.
The problem is that same switch would take 5x as much power to switch. Which means a modern 220w cpu would now need 1100watts of power :x
- jpmattia 12y ago> The problem is with carbon in general is it has a band gap 5x larger then Silicon. Which overall (but not entirely) means if you want to build a transistor with Diamond (or graphene) you need to put 5x as much voltage into it. I should have said electron affinity rather than electronegativity: You're not trying to get electrons from the valence band into the vacuum, just from the conduction band to the vacuum. Diamond actually has a negative electron affinity, which is why the vacuum electronic folks were excited about it.
- ars 12y agoYou started by saying 5x voltage, switched to 5x power, and ended with 5x energy. Those are not the same thing. You can have 5x voltage without changing the power or the energy.
- marcosdumay 12y agoYou can have 5x the voltage without changing the power consumption if you reduce the capacitance. If you keep the transistors at the same size, a computer working with 5x mode voltage will use 5x more power if operating at the same frequency. (But you can probably make it run faster...) That said, except for very few embedded applications, computers today operate on a voltage that's much bigger than the silicon band gap. I'm not convinced it'd be a problem.
- cfallin 12y agoActually, all else being constant, 5x voltage yields 25x power: P = CV^2 * f (multiply by activity factor if pedantic; assuming all transistors toggle every cycle here.)
- marcosdumay 12y agoAnd, of course, you are right.
- tesseract 12y agoThe silicon band gap is ~1.1V at room temperature. Mainstream modern processor core voltages are around 1.2V (maybe less for the very latest parts) and "ultra low voltage" processors operate as low as 0.7V.
- kken 12y ago>The problem is with carbon in general is it has a band gap The band gap is not a function of the element alone, but mainly of the crystal structure. Different allotropes of carbon have vastly different band structures. Diamond has a high band gap, as you mentioned. But Graphene has none, and that is one of the major obstacles of the material.
- valarauca1 12y agoThe problem with having none is that makes your transistors even more vulnerable to quantum effects.
- typon 12y agoThat's not the main problem. The main problem of not having a bandgap is that you don't have a transistor...
- kken 12y agoSshhh.. It's not allowed to talk in that way about the graphene "transistor". You may upset certain funding sources. But you know, it is really fast! Just almost useless transconductance and no off state, but we can fix it later!
- typon 12y agoBut bilayer graphene has an induced bandgap!! What? The mobility goes to shit as soon as you touch it with a substrate? Well that's not a problem, we'll design vacuum suspended GFETs, but I'll get right back to you when I figure out how to put an oxide around that sucker