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Design and Fabrication of an EGFET Based Chemical Sensor Using Transistor Association Technique

Ion sensitive field-effect transistor (ISFET) and extended–gate field-effect transistor (EGFET) based biosensors are widely used devices for monitoring biological–processes such as enzymatic and antigen-antibody reactions, as well as nucleic–acid hybridization. Most of the recent field-effect based biosensors reported in the literature, utilize commercial analog front-ends for easier development, even though the continuous miniaturization and the consolidated complementary metal-oxide semiconductors (CMOS) technology allows to work at low-voltage/low-noise maintaining circuit reliability. To improve the performances with respect to commercial electronic interfaces, this paper presents a comprehensive study of the design and fabrication of an EGFET by using transistor association technique, designed in standard 130 nm CMOS process. Simulation and experimental results show that the DC equivalence with a single transistor with an input-referred noise ranging from 352.7 to 176.4 nVrms from 0.1 to 10 Hz. Prototypes are investigated in a real case scenario as a pH sensor which showed a voltage sensitivity of ≈ 58 mV/pH with linearity higher than 99%. A prototype has been tested in clinical settings for the analysis of pH in urine samples in comparison to the standard reactive strips.