I am looking for a capacitor with good temperature stability to replace some low value ceramic caps in a bandpass filter. If I understand it correctly, the best types are PPS (poly phenylene sulfide). However, at the values I want, 47p and 82p I cannot find a COTS supplier in 0805 packaging.
What is the next best capacitor type, and how much worse is it than PPS (and how much better than ceramic)?
Temperature stability of SMT capacitors is typically specified by selecting a type known as a C0G or NP0 capacitor. These Class 1 capacitors are made to be temperature compensating and are made of non ferro-electric materials to yield superior stability.
As far as understanding and comparing various capacitors you really need to download the manufacturers family data sheets and do the specification comparisons yourself to see if any particular type will meet your needs.
Another factor to consider is that if your filter circuit includes other components such as resistors and opamps these may also have performance changes with temperature.
NP0/C0G ceramic caps are pretty good- maximum +/-30 ppm/degree C- to do substantially better would be dramatically bigger and more expensive.
For example you could machine an Invar structure and use dry N2 as the dielectric.
Stray capacitances on FR4 can have high tempco which will affect your total. Careful layout (avoid ground planes) and maybe better $$$ materials such as PTFE.
