Influence of oxygen content on the structural and sensing characteristics of Y2O3 sensing membrane for pH-ISFET

This paper describes the physical and sensing characteristics of Y2O3 sensing membrane grown on Si substrates through reactive rf sputtering. The structural and morphological features of these films were investigated using X-ray diffraction, atomic force microscopy and X-ray photoelectron spectroscopy. We find that the electrolyte-insulator-semiconductor structure with Y2O3 sensing membrane prepared under an argon-to-oxygen flow ratio of 25/5 and annealed at 800 °C exhibited a higher sensitivity of about 54.5 mV/pH in the solutions from pH 2 to pH 12, a smaller drift rate of 2 mV/h in the pH 7 buffer solution, and a lower hysteresis voltage of 4.78 and 6.39 mV in the pH 7 → 4 → 7 → 10 → 7 and pH 7 → 10 → 7 → 4 → 7 loops, respectively. We attribute this behavior to (a) the presence of small amounts of oxygen in the sensing film preventing Y-silicate or amorphous silica from forming at the Y2O3/Si interface and (b) the low surface roughness.