Electrolyte-insulator-semiconductor devices with different integrated reference electrodes for pH detection

Abstract

Electrolyte-insulator-semiconductor (EIS) devices were fabricated with different integrated reference electrodes, including aluminum (Al), alumina (Al2O3)/Al, titanium nitride (TiN), and graphene/TiN. A titanium oxide (TiO2) film as a gate dielectric and pH sensitive membrane was used in all EIS devices. Structural characterization by Raman spectroscopy indicated that the TiO2 film comprised 20% anatase and 80% rutile crystalline phases and was an appropriate gate dielectric for EIS and ion-sensitive field-effect transistor (ISFET) device applications. Capacitance versus voltage (C–V) measurements were carried out with solutions with pH values of 4, 7, and 10 dripped on the EIS devices. The C–V curves produced the flat-band voltages (VFB) for each solution, whose dependence on the pH value determined the pH sensitivity of EIS device. The best results in terms of the chemical stability and a pH sensitivity of 13 mV/pH were exhibited by the TiN reference electrode, which can be integrated in ISFET (or EIS) devices with monolithic complementary metal–oxide–semiconductor applications.