A hydrophobic polymer such as parylene has ion dissociation sites of extremely low density. An electrolyte-parylene interface manifests a constant potential independent of solution composition. The parylene-gate ISFET can be used as a solid state reference electrode. These films can also be used for the substrate of a CHEMFET, where the recent chemical modification technology is introduced. In this paper, the concept of a parylene-gate ISFET based on the site-binding model is investigated. As applications, a probe-type all solid state pH sensor integrating an Si3N4 gate, a parylene gate and an Au pseudo-reference electrode is discussed. A pK ISFET chemically modified with crown ether compounds is also reported.
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