A field effect transistor for use as an ion sensor has a P-type silicon substrate on which are formed a source region and a drain region. An N-type isolation diffusion layer is formed on the outer peripheral surface of the silicon substrate and this diffusion layer is surrounded by an insulation layer....http://www.google.com/patents/US4903099?utm_source=gb-gplus-sharePatent US4903099 - Field effect transistor for use as ion sensor
