RobG wrote on Jan 2nd, 2012, 8:29am:On another site a person was wondering how much a poly resistor would self heat if dissipating ~2.5 mW @ 2mA. I would have dismissed it, but I guess it can be a problem. Poly is encased in oxide so the thermal resistance to the outside world is relatively high. Do any of you know about what to expect for temp increase, or the typical recommended current density for poly?
Foundry specifications for current density should be your guideline here.
It will be foundry unique due to thickness of the poly layer.
Heating of substrate can be done using the total
wattage on chip and the thermal (degrees C/watt)
rating of the package.
Localized heating on the die is a little toughter.
You can do a thermal model and estimate the thermal
conductivity of each layer and all that. Its a time consuming
PITA. If you got silicon, you can do an infrared photo to
see whats "hot or not"
From prior work, a hot element on die, tends to conduct pretty well
to whats around it. (based on the "hot or not" pixs) Thermal
isolation of oxides, probably not that good
because the oxides are so thin.
Best I got.