[SI-LIST] Re: Temperature vs. performance in different type of processes.
- From: "Ingraham, Andrew" <Andrew.Ingraham@xxxxxxxxxx>
- To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Fri, 13 Jul 2001 19:40:08 -0400
> "CMOS,Bipolar and BI-CMOS processes each have unique characteristics that
> determine these
> performance conditions." said in the article.
>
> Can somebody shed some light on it? Why do they have different temperature
> defined for maximum and minimum conditions?
>
It is a function of the physics of bipolar vs. MOS transistors.
For bipolars, recall that the current through a semiconductor junction at a
given voltage increases as the temperature increases. That's just how they
work. Bipolar transistors are "stronger" (conduct more) and generally
switch faster when they get hot. (This was what made linear bipolar amps
susceptible to "thermal runaway.")
I don't recall off-hand the physics that determine temperature dependency
for MOSFETs, but the end result is that they switch faster at lower
temperatures. Cryogenic cooling is used on some faster CMOS computers. You
can even buy "souped up" computers with a built-in refrigeration unit
attached to the CPU.
> What is for BI-CMOS?
That depends on the individual Bi-CMOS circuit. It could go either way.
Heck, I suppose it could be nonlinear with the fastest (or slowest) point in
the middle of the temperature range. (There's no one way to design a
circuit and call it "Bi-CMOS.")
Regards,
Andy
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