Annealing temperature effect on the electrical characteristics and pH sensitivity of TiO2/ZnO bilayer films

The effect of annealing temperature on the surface morphology and electrical properties of composite bilayer, TiO₂/ZnO were studied in this investigation. The composite thin films were applied as the sensing membrane of an Extended Gate Field-Effect Transistor (EGFET) based pH sensor. TiO₂ and ZnO were deposited on Indium Tin Oxide (ITO) by using sol-gel spin-coating process. The effects of the varied parameter on the sensor sensitivity and linearity were also investigated. The sensitivity of the TiO₂ thin film towards pH buffer solution was measured by dipping the sensing membrane in pH4, pH7 and pH10 buffer solution. In addition, these thin films were characterized by using Field Emission Scanning Electron Microscope (FESEM) to obtain the surface morphology of the composite thin films. Meanwhile, I-V measurement was done in order to determine the electrical properties of the thin films. According to the result obtained in this experiment, thin film that annealed at highest temperature, which is 500°C produced highest sensitivity, 53.3 mV/pH. Relating the I-V characteristic of the thin films and sensitivity, the sensing membrane with higher conductivity gave better sensitivity.