I'm trying to understand why an ISFET needs a reference electrode. I have looked up several answers online but still dont understand. I have drawn out the doping, a MOSFET and the ISFET:

Mosfet Isfet In my mind, a change in pH changed the H concentration around the sensing pad which changed the properties of the channel?

  • \$\begingroup\$ Can you apply a gate voltage to the normal FET with only the + side of a battery? You need a reference, and that is what the reference electrode is for. It completes the circuit. \$\endgroup\$ – LukeHappyValley Sep 30 at 10:00
  • \$\begingroup\$ Doesn't the accumulation of H+ due to low pH create an electric filed anyhow? I imagine that connecting only to the positive side of a battery would cause some electrons to move into the wire as they are attracted by the excess + charge. ? \$\endgroup\$ – leo electrics Sep 30 at 10:15
  • \$\begingroup\$ @lukeHappyValley my intuition actually makes me think that I would still see an effect if I connected to only the positive terminal of a battery. \$\endgroup\$ – leo electrics Sep 30 at 10:25

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