The effects of sensing electrode thickness on ruthenium oxide thin-film pH sensor

• A compact accurate pH sensor employing a RuO2 thin film sensing electrode.
• Integration of RuO2 electrode with electroplated Ag/AgCl reference electrode.
• Effect of sensing electrode thickness on pH sensing accuracy is investigated.
• pH sensitivity of 68.63 mV/pH is demonstrated for 300 nm thick sensing electrode.
• Experimental results demonstrate excellent pH sensor performance.

A miniaturised pH sensor structure employing an R.F. sputtered ruthenium oxide sensing thin-film electrode in conjunction with an electroplated Ag/AgCl reference electrode is developed and the effect of the thickness of the sensing electrode on the measurement accuracy is investigated. Experimental results show that the pH sensor exhibits Nernstian slopes of 66.52 mV/pH, 68.63 mV/pH, 67.73 mV/pH, and 54.83 mV/pH for ruthenium oxide film thicknesses of 425, 300, 175 and 50 nm, respectively. All the pH measurements were carried out at a temperature of 22 °C. The performance and characterisation of the pH sensors in terms of sensitivity, response time, pH resolution, stability and reversibility are discussed.