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I understand that companies heavily invested in silicon would like to portray it that way, but CPU frequencies haven't ceased to grow. DARPA manufactured a THz

by tagrun 9y ago

I understand that companies heavily invested in silicon would like to portray it that way, but CPU frequencies haven't ceased to grow. DARPA manufactured a THz transistor made of InP back in 2014. Silicon isn't the only semiconductor in nature, and others are actively being researched. Also, "when you increase the frequency you increase the power" (which is their argument) doesn't explain why they can't increase the frequencies. That was always the case even back in 1960s. What they actually need to explain is why they can't make the silicon more power-efficient anymore; all toy-physics arguments (such approximations/linearizations work only for a very limited range of frequencies, if they do at all, anyway meaning their scaling-relations aren't universal like they're trying to portray and those coefficients they ignore aren't constant across voltage, frequency, materials, ... either; you almost never get such simple and universal answers in condensed matter physics even for much simpler problems) mentioned there could have been made 50 years ago as well, but silicon CPU frequencies did go up.

tarlinian 9y ago
Transistor switching frequency has almost nothing to do with processor clock speeds which are almost entirely limited by wire RC delay. You will get increased drive currents by switching to higher mobility materials but the performance improvement over strained silicon isn't that large.
- tagrun 9y ago
  That's just a plumbing problem which can be solved by lowering temperature or using a different material with lower resistivity. Yes, it'll probably cost more, but it's a problem that can readily be solved. But if your switching frequency is slow, it doesn't matter if you use a superconductor for wires. It is the switching frequency that truly determines the limits for gate times, which in turn determines how fast your CPU is. For the record, SiGe is also very promising in terms of switching speeds. There were experiments which shows near THz frequencies.
  - deepnotderp 9y ago
    >That's just a plumbing problem which can be solved by lowering temperature or using a different material with lower resistivity. Yes, it'll probably cost more, but it's a problem that can readily be solved. No it's not. What is this magical material with ultra low resistance? And how do you plan to reduce capacitance? Btw, manufacturing terahertz speed transistors is very difficult. There are Mott FETs which will switch at 10 terahertz, but they're incredibly hard to manufacture and very power hungry.
    - d-sc 9y ago
      I can’t speak on their usability in circuits. However, materials that show properties characteristic of zero resistance exist. I’ve used them at work before. https://en.wikipedia.org/wiki/Superconductivity https://en.wikipedia.org/wiki/Superconductivity
      - deepnotderp 9y ago
        And how do you propose to cool every chip to cryogenic temperatures? Not to mention the manufacturing challenge of integrating superconductors into chips (I think InP would be the easiest candidate, and that's saying something...)
    - tagrun 9y ago
      There's nothing magical about it. As has been pointed out, chips with superconductors has been a thing for a long time (at least in experimental physics) and there's nothing magical about it, but resistivity is a (nonlinear) function of temperature and lowering it almost always lowers the resistance, so you can achieve this to an extent even with non "magical" materials without going to cryogenic temperatures. You don't have to reduce the capacitance; you'll be fine as long as you can lower the resistivity. Do you have any references for FETs that switch at 10THz? I've never heard of it and I'm interested in the physics of it.

by tagrun 9y ago

tarlinian 9y ago

Transistor switching frequency has almost nothing to do with processor clock speeds which are almost entirely limited by wire RC delay. You will get increased drive currents by switching to higher mobility materials but the performance improvement over strained silicon isn't that large.

tagrun 9y ago
That's just a plumbing problem which can be solved by lowering temperature or using a different material with lower resistivity. Yes, it'll probably cost more, but it's a problem that can readily be solved. But if your switching frequency is slow, it doesn't matter if you use a superconductor for wires. It is the switching frequency that truly determines the limits for gate times, which in turn determines how fast your CPU is. For the record, SiGe is also very promising in terms of switching speeds. There were experiments which shows near THz frequencies.
- deepnotderp 9y ago
  >That's just a plumbing problem which can be solved by lowering temperature or using a different material with lower resistivity. Yes, it'll probably cost more, but it's a problem that can readily be solved. No it's not. What is this magical material with ultra low resistance? And how do you plan to reduce capacitance? Btw, manufacturing terahertz speed transistors is very difficult. There are Mott FETs which will switch at 10 terahertz, but they're incredibly hard to manufacture and very power hungry.
  - d-sc 9y ago
    I can’t speak on their usability in circuits. However, materials that show properties characteristic of zero resistance exist. I’ve used them at work before. https://en.wikipedia.org/wiki/Superconductivity https://en.wikipedia.org/wiki/Superconductivity
    - deepnotderp 9y ago
      And how do you propose to cool every chip to cryogenic temperatures? Not to mention the manufacturing challenge of integrating superconductors into chips (I think InP would be the easiest candidate, and that's saying something...)
  - tagrun 9y ago
    There's nothing magical about it. As has been pointed out, chips with superconductors has been a thing for a long time (at least in experimental physics) and there's nothing magical about it, but resistivity is a (nonlinear) function of temperature and lowering it almost always lowers the resistance, so you can achieve this to an extent even with non "magical" materials without going to cryogenic temperatures. You don't have to reduce the capacitance; you'll be fine as long as you can lower the resistivity. Do you have any references for FETs that switch at 10THz? I've never heard of it and I'm interested in the physics of it.