Preparation and properties of hydrogen ion-sensitive field effect transistors with sol–gel-derived Mg-modified lead titanate gate

A sol–gel-derived Mg-modified lead titanate (PMT) membrane has been applied successfully as a novel hydrogen ion-sensitive layer. The fabrication parameters and characteristics of the amorphous PMT membrane are determined at a firing temperature of 350–450 °C and Mg content below 7 mol% via differential thermal, thermogravimetric and X-ray diffraction analyses. The optimized fabrication parameters of the PMT membrane for hydrogen ion-sensitive field effect transistors (ISFETs) include a Mg content of 4–5 mol%, thickness of 0.5 μm and firing temperature of 400 °C. These parameters were determined via capacitance–voltage measurements of the electrolyte–insulator–semiconductor structure. These membranes exhibit a quasi-Nernstian response of 58–59 mV/pH, good surface adsorption and corrosion resistant characteristics. The output characteristics of the PMT gate ISFET are very similar to those of metal oxide field effect transistors at a specific pH concentration. In the saturation region, the pH response and linearity can be controlled by adjusting the gate–source voltage (VGS), e.g. the pH responses of −8.4, −24.3 and −32.7 μA/pH and the correlation coefficients of 0.99067, 0.99959 and 0.99963 at VGS=1, 3 and 5 V can be obtained, respectively. In the non-saturation region, a linear pH response exists at about 59 mV/pH.