As the title states, what is the smallest value of resistor that can be
reasonably put on chip. I will be using the 0.25micron standard process.
I need it to be small so that efficiency will not suffer.
Thank you.
It depends on what do you mean by a "standard" process.
You did not mention what kind of resistances you are looking at.
Too small, and your parasitics may overwhelm it, and process variations may be large as well.
If you use metal then the value can be very small. Not
super well controlled. Silicided poly would probably be
the next step up.
If you are trying to dissipate power in a small geometry,
be sure you understand the electomigration (aluminum
and soft silicides) and power density (thin film resistors)
limits. You may find information on the latter, lacking.