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Strained Silicon to Perpetuate Moore's Law
An anonymous reader noted a story floating around about a new technology known as strained silicon (or maybe 'Stained' since the article calls it both ;) which AMD & IBM figure will make CPUs 24% faster. A little bit on how it works as well, but not much substance.
Strained silicon is a great technology. you get 30% (or whatever) better electron mobility, which makes for faster capaciter discharge, and thus faster transister switching, and reduced heat generated in the process. However, you can't strain it much more than they already have. It bought the lithography folks another few hundred megahertz, but it's not going to keep moore's law alive for another couple decades, at least not by itself.
Strained silicon doesn't really address the two big problems facing silicon lithography: leakage current, and the ever rising costs of dynamic power costs. Even with strained silicon there are still hundreds of millions of capacitors, each charging and dischanrging billions of times a second. If the frequency increases by some number X and the number of caps increases by some number Y, you have to drop the charge on each cap by X*Y or the dynamic power usage goes up. Furthermore, leakage current, which used to contribute almost nothing to the energy needs of a CPU, now makes up a good percent of the electrical and heat budgets. The drains are just too close to the body. There are too few atoms of semiconductor to act as a resistor.
It's a nice one-time speed bump, but it does solve the hard problems, just puts them off for another year.
Alternating thin layers of different lattice constant materials can change the semiconductors properties, in particular, the bandgap. It is possible to turn Si into a direct-bandgap material (like GaAs) this way.
The problem in large scale mfg (back then) was eliminating crystaline defects.
Not really... read it again, they talk about removing the stuff from the new CPUs for AMD and IBM. From what I understand Intel does not remove it.
Just a note,
Intel has been using strained silicon since Prescott. They made the same claims before releasing it. But we can see now that it really doesn't make much of a difference so they're removing the emphasis from clock speed and optimizing for lower speeds.
Nothing to see here. Old news.
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What ever happened to the idea of using a diamond substrate for chips instead of silicon? I remember reading about this 6 months ago: some MTI group were perfecting a system that could manufacture diamonds in a high-temp/pressure chamber, cheap enough that it would be viable to use instead of silicon. The diamond was supposed to have much better thermal properties and allow much faster chips....
And a slight addition: It does not perpetuate moores law, it is just mitigating the problems that occured with gate dielectric scaling.
Moore's Law requires constant downscaling of the gate insulator in the transistor. Recently the industry came to a point where the tunnelling current through the insulator became so high that it is not possible to make it any thinner. This problem can be counteracted by increasing the channel mobility using strained silicon.
But still even for small blocks (like your 16 bit adder) where lines are relatively short, charging and discharging of gate capacitance (expecially for modern thin gates) is another limiting factor in both speed (RC) and power (F*CV^2/2).
A related thing (that I personally worked on for many years) is how do you build general-purpose computing logic where you connect gates not with your standard "wires" but with real (matched) transmission lines. Belive me, it is not a trivial task, even if you have an ideal transmission lines (i.e., superconducting) and your active devices can operate at hundreds of GHz, you STILL get your "clock frequency" in the order of several 10s of GHz for small blocks, not hundreds.
Paul B.
It bought the lithography folks another few hundred megahertz, but it's not going to keep moore's law alive for another couple decades, at least not by itself.
This has been true for every innovation since before Moore first made his observation that is now known as Moore's Law.
To get a 100% increase in transistor count (or popularly and probably more relevently, processor performance) every 18 months has required numerous individual ideas, each of which is worth a one-time-only boost of 30%, 20%, 10%. Hell, a lot of times we're happy with 1%. Moore's Law isn't a Law like gravity, it's a testament to how successfull engineers have been in finding those 10%, 20%, 30% increases repeatedly and consistantly for several decades. There have been predictions that Moore's Law would end due to some problem for almost as long, and the truth is that it would end if the stream of innovations like strained silicon ever stopped.
You probably realize that, I just wanted to state it explicitly for those who may think Moore's Law is some trend that will continue on its own until some major roadblock is hit. There's always a major roadblock but engineers keep finding ways around them because they rock.
Oh, and I agree that the major problems today are wire capacitance and leakage current. Wire cap has been known as a big hurdle for quite a while, since just from the math you could tell that when you scale down the transistors get smaller and faster but the wire cap stays constant. Leakage current seems to have more or less snuck up on the industry, though, and it's causing some shakeups that may disrupt Moore's Law for a bit. You can already see it if you look at performance graphs for the last few years.
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I mean, lets say things just suddenly stop and say 10ghz is the max chip speed and every other thing intel tries explodes the chip within 10 seconds. So maybe intel folds because of that (I'm a bad american... I really don't care about a companies right to profit. (i also have corporate grammar)) But some other chip maker can then take this speed limit and generate a process to develop that chip for extremely low level costs. Or maybe other people come along and argue for power and heat friendly chips which are only slightly less than the upper bounds.
Then us software people start to run out of the excuse of "Hey, you should upgrade, then it'll run faster." And we can get down to the business of making the software just work correctly without having to worry about the next big thing we should be taking advantage of (sadly Game devs are still screwed for many more years.) We might even take the time to build software to eek out every possible advantage from the cpu ... you know ... back like we did when we thought 640k would be enough for anybody.
Then give it a few years... say 50. And suddenly bio computing or quantum computing takes shape and a new industry of chip design is born and bolsters us into the next phase... but in the meantime we've done a good job of building a nice little base in the phase we are in. Use it as a benchmark against the designs of the next phase.
I guess I don't see hitting this wall a bad thing. It seems that knowing there's a wall in front of you stimulates more in trying to get around the wall than seeing an endless open field does in making you feel like you might as well just sit down and take a breather.
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