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Is it temperature or voltage that kills/degrades chips? - Page 4

post #31 of 33
I would hazard a guess that it's thermal expansion, the reason why you don't have chips dying instantly on LN2 @ 2V is because under LN2 you often have very low temperatures and that shrinks the gates but mostly always heat is the problem which causes the other 2 gates to expand towards each other and in the end you have a shorted transistor

That's what i think, after observing a mosfet that was put under abuse (overvoltaging and inadequate heatsink) on purpose under a microscope
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post #32 of 33
Voltage, current, and temperature all contribute to electromigration.

Thermal expansion/contraction rarely plays a significant role outside of extreme cooling, and when it does, solder joins are usually what fail.
Quote:
Originally Posted by ronnin426850 View Post

The idea that good coolers allow you to get away with any voltage is wrong. The voltage's dependency on the cooling goes as far as its relation with temperature. But voltage is not just this thing that heats up CPUs. It also fries them smile.gif Even if you run your CPU on LN2, you can't overvolt it sky high and expect it to live.

Reduce anyone of the above factors and you can get away with higher on the other two with the same longevity.

Every 10C you knock off very roughly double's lifespan (see Black's Equation). This is why you can use voltages under L2 that would destroy a conventionally cooled part in seconds.
Quote:
Originally Posted by DaveLT View Post

low temperatures and that shrinks the gates but mostly always heat is the problem which causes the other 2 gates to expand towards each other and in the end you have a shorted transistor

A 300C temperature change is not enough to significantly alter gate size or distance. You can fracture a die (microscopically or otherwise) with rapid cooling or heating, but the gates do not move enough relative to the silicon they are built on to come anywhere near close to shorting.
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post #33 of 33
Quote:
Originally Posted by Suyer View Post

With regard to this, I'd say that temperature is less of an issue of "thermal degradation" of compounds as it is an issue of diffusion. As you mentioned, these transistors are on very small scales, (hundreds of atoms), so I think the issue with temperature is that the doped semiconductor materials usually used in the source/drain within the transistor will slowly degrade over time due to thermal migration of the doped atoms between the p-type and n-type regions. I.e. looking at this picture:



At any temperature (above 0 K), you will get diffusion of the p-type dopant into the n-type channel and vice versa. Over time (a very significant time at 25 C), you will reach a state where the distribution of dopants is exactly the same over the source, drain, and channel, and at that point the transistor will not work at all (and probably will stop working long before that due to leakage current as the semiconductors lose their doping). Since this is due to diffusion, and typically diffusion is proportional in increase to T^(3/2), you're seeing an exponential increase in degradation due to dopant migration at higher temperatures. It's time based, so it's unlikely you'll kill your chip immediately in virtually any case where you go to a high temperature because of this, you'd have to be more worried about something melting/burning at that point. But over time, higher temperatures will lead to this process happen significantly faster as many of you have already conjectured.

It's probably possible to calculate exactly how long this process would take at various temperatures if the dimensions and dopant levels of the current Intel finfet transistors are known. I also think that this is probably where companies like AMD/Intel get their lifespans from, and target operating temperatures. For example, AMD has said that their new R9 290 card is supposed to operate at 95 C for it's lifetime, and that it's not an issue. I've personally thought that it's silly that people complain about the temperature on the cards after this, because really what AMD is telling us is that at 95 C, the card's structure will not change due to diffusion to make it unusable during it's lifetime. They probably have done this calculation on rates of dopant migration. Of course this principal can be applied to other parts of the card as well, such as the cache etc... and I don't really have knowledge about how those structures look, but in theory they should suffer from the same issue.

With regard to voltage, I was always under the impression that higher voltage just means that you can have significantly higher levels of quantum tunneling through regions where otherwise you wouldn't have it. I can't really think of a reason why increased electron movement would actually cause damage. Perhaps I'm thinking about this wrong, but it's not like the electron is crashing through the channel or the gate dielectric and forming a short circuit path in it's wake. It's really just jumping from one side to another via the quantum tunneling phenomenon. My guess would be that higher voltages lead to high local temperatures due to increased resistance, and this could possibly be causing localized defects, particularly on the interfaces of different materials, such as the metal in the source/drain and the semiconductor material next to it. Possibly why you don't have chips dying at 2V when they're cooled by LN2. I can image that your CPU probably would instantly die on air at that voltage.

This is all speculation though, similar to the above poster I am a Chemical Engineer, so most of this is based off of how materials tend to act under various physical conditions.
Very interesting too, now what's the conclusion...does the increased voltage speed up the degradation of transistors or not? Looking forward for my own studies to convince myself with my own eyes and brain...
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