Study on pH at the point of zero charge of TiO2 pH ion-sensitive field effect transistor made by the sputtering method

In this article, the current-voltage curve of an ion-sensitive field effect transistor (ISFET) is used to find the pHpzc (pH at the point of zero charge) of a pH-ISFET device. The pHpzc is an important parameter of a pH-ISFET device that is used directly to obtain the relationship between the equilibrium constants, Ka and Kb, and pH sensitivity. In this study, titanium dioxide (TiO2) acted as the sensitive membrane of a pH-ISFET, and was deposited by the sputtering method with a thickness of about 250 Å. A Keithley 236 Semiconductor Parameter Analyzer was used to measure the drain-source current (IDS) versus the gate voltage (VG) curve at room temperature. Furthermore, this was used to determine the sensitivity of the TiO2 pH-ISFET, and then this information has substituted into the theoretical metal oxide semiconductor field effect transistor (MOSFET) model to determine the ISFET threshold voltage. Thus, the surface potentials of the TiO2 pH-ISFET for different pH values were obtained. Furthermore, it is well known that when the pH is equal to the pHpzc the surface potential must be zero and accordingly, we attained a pHpzc of 6.2 for the TiO2 pH-ISFET.