Spin Speed and Duration Dependence of TiO 2 Thin Films pH Sensing Behavior

Titanium dioxide (TiO 2 ) thin films were applied as the sensing membrane of an extended-gate field-effect transistor (EGFET) pH sensor. TiO 2 thin films were deposited by spin coating method and the influences of the spin speed and spin duration on the pH sensing behavior of TiO 2 thin films were investigated. The spin coated TiO 2 thin films were connected to commercial metal-oxide-semiconductor field-effect transistor (MOSFET) to form the extended gates and the MOSFET was integrated in a readout interfacing circuit to complete the EGFET pH sensor system. For the spin speed parameter investigation, the highest sensitivity was obtained for the sample spun at 3000 rpm at a fixed spinning time of 60 s, which was 60.3 mV/pH. The sensitivity was further improved to achieve 68 mV/pH with good linearity of 0.9943 when the spin time was 75 s at the speed of 3000 rpm.