Ion-sensitive field-effect transistors with inorganic gate oxide for pH sensing

Ion-sensitive field-effect transistors (ISFET´s) have been fabricated by using silicon films on sapphire substrates (SOS). Using this structure SiO2, ZrO2, and Ta2O5films are examined as hydrogenion-sensitive materials, and Ta2O5film has been found to have the highest pH sensitivity (56 mV/pH) among them. The measured pH sensitivity of this SOS-ISFET´s is compared with the theoretical sensitivity based on the site-binding model of proton dissociation reaction on the metal oxide film and good agreement between them is obtained.