The pH-sensing and light-induced drift properties of titanium dioxide thin films deposited by MOCVD

Titanium dioxide thin films were deposited on thermally oxidized silicon wafers by metal organic CVD (MOCVD). Then the resulting TiO2/SiO2/Si test structures were annealed in dry oxygen for 60 min at temperatures 700, 800, 900, and 1000 °C, respectively. Refractive index and relative permittivity of the as-deposited and annealed titanium dioxide layers were investigated by spectral ellipsometry and high frequency capacitance–voltage (HF-CV) measurements. The pH-sensing properties of the titanium dioxide layers were investigated by capacitance–voltage measurements on electrolyte/insulator/silicon (EIS) structures. In addition, light-induced drift of the test structures was investigated by illumination using 12 V light bulb for 60 min in a measurement chamber. The titanium dioxide layers revealed refractive index of 2.38–2.58 (λ=550 nm) and relative permittivity of 31.28–36.27. Integral pH-sensitivities (pH ranging from 3 to 11) of the titanium dioxide layers were 57.4–62.3 mV/pH (T=32 °C). All the titanium dioxide layers showed no light-induced drift. After long-term measurement, the titanium dioxide layer annealed at 900 °C revealed a better stability of the pH-sensing properties than other titanium dioxide layers investigated in this study.