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

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 13mV/pH were exhibited by the TiN reference electrode, which can be integrated in ISFET (or EIS) devices with monolithic complementary metal-oxide-semiconductor applications. Published by the AVS.