Patent ID: 8035175

Claim:
A field effect transistor for detecting ionic material, the field effect transistor comprising: a substrate formed of a semiconductor material; a source region and a drain region spaced apart from each other in the substrate and doped with an opposite conductivity type to that of the substrate; a channel region interposed between the source region and the drain region; an insulating layer disposed on the channel region and formed of an electrically insulating material; a first reference electrode disposed at an edge of the upper portion of the insulating layer; wherein the first reference electrode has an opening in the center thereof, exposing the insulating layer, and a second reference electrode disposed upon an upper surface of a separation layer and in intimate contact with the separation layer; the separation layer being disposed upon the source region, the drain region and the first reference electrode such that a lowest surface of the second electrode lies above a highest surface of the first electrode; wherein the separation layer comprises an electrically insulating material.