||Hydrogen ion-sensitive field effect transistor with sol-gel-derived La-modified lead titanate gate |
Department of Electrical Engineering, National Sun Yat-Sen University
*Jen-Fu Su **Ying-Chung Chen
In this thesis the amorphous lead lanthanum titanate (Pb1-xLaxTi1-x/4O3, PLT) membrane has been prepared by sol-gel method as a novel pH-sensitive layer. The lead lanthanum titanate membrane was directly deposited on the SiO2(1000Å)/p-Si substrate by spin-on coating to form the PLT/SiO2/Si EIS structure. The C-V measurement was used for examining the fabrication parameters and sensing properties. Moreover, the PLT membrane was grown onto the SiO2 gate ISFET as the PLT/SiO2 gate ISFET. The electrical properties with the different parameter conditions can be obtained by the I-V measurement.
Experimental results show that the fabrication parameters and characteristics of the PLT membrane are determined at the La-modified content about 3 mol% and the firing temperature of 400℃ via the EIS structure. There exhibits the pH response of about 44-52 mV/pH in the range of pH 2-12. Furthermore, the nonideal factors, such as drift of 0.1-0.3 mV/h, hysteresis of 2-13 mV and lifetime decay of about 72 mV/pH-day, can be also obtained via the I-V properties of the ISFET. Finally, the hardware architecture of pH measuring system has been built up. The system makes use of constant current and voltage bias technique to ensure that the variations of the output voltage can give directly the variations of pH value. For the purpose of achieving the function of data calibration and driving the liquid crystal display (LCD), the 8051 microprocessor is employed.
Keywords: ISFET, Sol-gel, Lead lanthanum titanate, Drift, Hysteresis, pH meter