ZnO Film Flexible Printed Circuit Board pH Sensor Measurement and Characterization

An electrochemical zinc oxide (ZnO) pH sensor is proposed and prototyped using a flexible printed circuit board (FPCB). The device is resistant to acidic and alkaline solutions and exhibits excellent electrical conductivity. The sensing film was deposited by radio-frequency sputtering, providing a dense ZnO layer, and (3-aminopropyl)triethoxysilane (APTES) was used to enhance the chemical stability of the ZnO in acidic solutions. The proposed pH sensor has an average sensitivity of 37.52 mV/pH, linearity of 0.995, and a repeatable RSD value of 2.4%. Testing was conducted with Carmody's buffer pH 2–10 and a voltage-time measurement system. The stability of the prototype was determined by the measurement of the drift and hysteresis effects.