> To me at least, the first part is obvious. As temperature goes up, so does
> resistance. The higher resistance requires a greater potential difference
> to send an adequeate(sp?) amount of current throught the processor.
> Without cooling, I would imagine the chip would eventually melt down. With
> cooling, I would imagine the voltage peaks out in some sort of gaussian
> curve.
For small temperature ranges then R = kT + c, the trouble is, for
semiconductors, k can be negative. This is why semiconductors
can (& do) burn out if overrun or undercooled - current can "run
away" to very large values (essentially whatever the supply rails will
stand before *they* step in & act as fuse wire)
When running digital chips very fast, what you need is a sharp
rise/fall. Now you just *never* see nice square waves like those
drawn in the text books, real signals tend to look like a sine wave.
Obviously, in these circumstances, the higher the voltage, the
steeper the rise & fall of the signal when it's changing from a 0
state to a 1 state, or vice versa.
It's also why small die sizes can be run faster than large die sizes,
the current is much smaller, so it takes less power to change from
0 to 1 in a given time.
> Which brings to mind a theory about the second part, "speed increase". Too
> much heat will damage a processor. However I wonder if there is a
> relationship between some sort of particle drift (electron???) and
> resistance that "breaks in" or "burns in" a new processor? Much like the
> performance on a new engine after it has been carefully broken in after
> the first 1,000 miles...
I get the impression that failure rates on (non-overclocked)
semiconductor device falls rapidly with time, at least over the first
few hours. This is why quality systems suppliers "burn in" or "soak
test" systems for 24-48 hours before shipping. It may be the case
that minor flaws can act as "pinch points" which eventually cause
burn out & failure, even though the chip actually measures within
spec to begin with. Also atoms within crystals can "creep" causing
minute changes to the circuit characteristics, I would have thought
that the most significant effect would be the first time the circuit
gets to its "normal" operating temperature.
Regards
Brian Beesley
