It is LM108 and LM112 (internally compensated) and there is de facto no trick there. It has 1nA enter bias which happens to be reasonably steady with temperature as in many bipolar opamps since β basically improves with temperature. Later iterations like LT1008/LT1012 or OP97 pushed it all the way https://low-noiseamplifier70246.blogthisbiz.com/41014420/the-5-second-trick-for-pin-diode-switch