Effect of silver doping on sol-gel synthesized RuAgxOy-based extended-gate field-effect transistor flexible sensor device

With the rising importance of pH detection in biomedical diagnostic applications and environmental monitoring systems, it is crucial to develop a highly efficient, cost-effective, and stable electrochemical pH sensor device. This study reports the effect of silver doping on the structural properties and electrical characteristics of the RuAgxOy films for an EGFET (extended-gate field-effect transistor) sensor. The RuAgxOy sensing film was fabricated by a sol-gel spin coating technique using different silver doping concentrations, i.e. 1, 3 and 5 mol%. These synthesized RuAgxOy films were determined by X-ray diffraction, atomic force microscopy, X-ray photo-electron spectroscopy, and energy-dispersive X-ray spectroscopy with elemental mapping to study their struc-tural properties, surface morphologies, chemical characteristics as well as their compositions and elemental distributions, respectively. The RuAgxOy sensor treated at an Ag doping concentration of 3 mol% showed a pH sensitivity of 61.38 mV/pH over the pH 2-12 range with an outstanding linearity of 0.996. This fabricated sensor exhibited an excellent reversibility associated with a lower hysteresis voltage of 3 mV and a smaller drift rate of 0.23 mV/h. Furthermore, the pH sensing performance of the RuAgxOy EGFET sensor processed with the 3 mol% condition remained constant after 500 repeated bending cycles. These results suggested that the smaller grain size, finer surface, and the presence of the metal Ag0 with larger atomic radius provide free electrons on the surface, resulting in elevated electrical conductivity of the RuAgxOy sensing platform.