INTEGRATED-ALL SOLID ELECTRODES pH SENSOR PERFORMANCE DEPENDENCY ON SILVER/SILVER CHLORIDE ELECTRODE THICKNESS

Environmental monitoring, biomedical research, and food processing require precise pH measurements; hence pH sensors are important. The glass-based reference electrode (RE) is the most common pH sensor but the fragility of the glass-based RE prevents it from being miniaturized. Thus, an integrated-all solid electrode (IASE) was fabricated where the Ag layer was thermally evaporated, followed by a chlorination process to form an Ag/AgCl RE, and a titanium dioxide (TiO2) thin film was used as the sensing electrode (SE) to form the integrated-all solid electrode (IASE). The influence of silver/silver chloride (Ag/AgCl) thin film electrode thickness (60, 120, 180, 240, and 300 nm) on the electrochemical-based pH sensor was studied. The IASE was applied as the extended-gate of field effect transistor (EGFET). The pH sensor sensitivity and linearity were evaluated for the IASE performance. As a result, the thicker the Ag/AgCl layer the higher the sensitivity. The 300 nm Ag/AgCl thickness showed promising sensitivity and linearity with 67.8 mV/pH and 0.9846, respectively.