Study on extended gate field effect transistor with tin oxide sensing membrane

Ion-sensitive field effect transistor (ISFET) is a device composed of a conventional ion-sensitive electrode and MOSFET device, applied to the measurement of ion content in a solution. Extended gate field effect transistor (EGFET) is another structure to isolate FET from chemical environment. In this study, the ISFET was separated into two parts. Tin dioxide (SnO2), obtained by sputtering, is used as a pH-sensitive membrane for electrode, which is connected with a commercial MOSFET device in CD4007UB or LF356N. The experimental data show that this structure has a linear pH response of about 56–58 mV/pH in a concentration range between pH 2 and 12. In addition, it is easier to fabricate and package the sensitive membrane structure and the measurement is simple for the application of disposable biosensor.