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 SiO
2
, ZrO
2
, and Ta
2
O
5
films are examined as hydrogenion-sensitive materials, and Ta
2
O
5
film 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.