Integrated solid-state electrode for extended-gate FET pH sensor / Aimi Bazilah Rosli

pH sensors considered as a crucial element in broad applications such as medical, agriculture and industrial. There are several methods used to detect the pH level as simple as a litmus paper to a complicated electronic device. Among them, extendedgate field effect transistor (EGFET) pH sensor is receiving significant attention due to its advantages such as low cost, simple structure and flexible shape. An EGFET system consists of a separated substrate containing sensing material connected to the gate terminal of a FET. The two electrodes that are essential for an EGFET system are sensing electrode (SE) and a reference electrode (RE). The conventional RE is a glass tube containing liquid electrolyte making it bulky and not suitable for miniaturization. To realize miniaturization of an EGFET sensor system, the SE needs to be sensitive and RE needs to be in solid-state form. In addition, these solid-state electrodes also need to be fabricated onto one substrate to allow sensor miniaturization. Among the material used for SE, zinc oxide (ZnO) is a preferable material due to its versatile properties in terms of physical and electrical properties. Other than that, ZnO also was known for its various nanostructure morphologies.