Effect of silver doping on sol-gel synthesized RuAg_xO_y-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 RuAg_xO_y films for an EGFET (extended-gate field-effect transistor) sensor. The RuAg_xO_y 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 RuAg_xO_y films were determined by X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy with elemental mapping to study their structural properties, surface morphologies, chemical characteristics as well as their compositions and elemental distributions, respectively. The RuAg_xO_y 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 RuAg_xO_y 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 RuAg_xO_y sensing platform.