A novel SnO2/Al discrete gate ISFET pH sensor with CMOS standard process

In this paper, we present a method allowing industrial production of integrated ion sensitive field effect transistor (ISFET) sensor. An ASIC CMOS standard process is used to integrate the sensor and signal processing circuit; then the sensor is plated with the sensing membrane (SnO2) by sputtering. The structure of the ISFET is novel SnO2/Al discrete gate. The discrete gate ISFET and the readout circuit were fabricated with a conventional standard CMOS IC process where no extra mask was required. The experimental data show that the SnO2/Al discrete gate ISFET sensors have a high linearity of 58 mV/pH in a concentration ranging from pH 2 to 10. The low offset and low power readout circuit for the discrete gate ISFETs pH sensor was designed and evaluated for monolithic in this study.