Abstract
Ion-sensitive field effect transistors (ISFET’s) have many advantages than the conventional ion selective electrode because of the small size of their sensitive area, robustness, rapid response, high sensitivity, low output impedance, low sample volumes, batch processing capability, low cost and the potential for on-chip circuit integration. The main part of an ISFET is the usual metal oxide silicon field effect transistor(MOSFET) with the gate electrode replaced by chemically sensitive membrane, electrolyte and a reference electrode (RE). Like in MOSFET, the channel resistance in ISFET depends on the electric field perpendicular to the direction of the current. Charges from solution accumulate on top of this insulating membrane and do not pass through the ion-sensitive membrane. Hence, the pH value of the solution can be detected by the ISFET. In this thesis, the barium titanate (BaTiO3) thin film was prepared by sol-gel method to be the sensor gate of ISFET. The barium titanate thin films were deposited on SiO2(1000A)/p-Si substrates by spin-on coating method, and the EIS structure was obtained. The flat-band voltage(ΔVBF) can be shifted by C-V measurement. The optimum conditions were found that the fluxing temperature was 110℃ and fluxing time was 4.5 hours, and firing temperature was about 340℃ and thin film thickness was about 1μm, and the sensitivity of 55.8 mV/pH in the range of pH1~pH11 can be obtained.