Preparation and characteristics of ruthenium dioxide for pH array sensors with real-time measurement system

Ruthenium oxide (RuO2) thin film was used as the sensing layer of hydrogen ion selective electrodes (ISE) for pH array sensors. The RuO2 sensing membrane was deposited onto a silicon wafer substrate using radio frequency sputtering technology. We measured the IDS–VG curves of the RuO2 sensing membranes connected to a MOSFET with conducting wire and immersed in the pH buffer solutions at different pH concentrations using a Keithley 236 Instrument. The results obtained the pH sensitivity of the RuO2 sensing membrane for the ISE devices at about 55.64 mV/pH. From the nonideal characteristic experimental results, the drift rate of the RuO2 ISE device was obtained at 0.38 mV/h at pH 7. The hysteretic widths of the RuO2 ISE device were 4.36 mV and 2.2 mV in pH 7–4–7–10–7 and pH 7–10–7–4–7 loop cycles, respectively. The RuO2 ISE was used for the pH array sensors structure to reduce the measurement error and testing time for four single sensors. And the reproducibility, stability, selectivity and response time of RuO2 array sensors were investigated. A real-time measurement system for pH array sensors was achieved. The system has the following advantages: portable USB DAQ card, easy to setup and use, with an application program development by the Visual Basic software, which is easily used in other computers.