Structural and sensing characteristics of Dy₂O₃ and Dy₂TiO₅ electrolyte-insulator-semiconductor pH sensors

In this paper, we describe an electrolyte-insulator-semiconductor device for biomedical engineering applications prepared from Dy₂O ₃ and Dy₂TiO₅ sensing membranes deposited on Si substrates by means of reactive radio frequency sputtering. The structural and morphological features of these films with annealing at various temperatures were studied by X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy. Compared with the Dy₂O₃ film, electrolyte-insulator-semiconductor devices incorporating a Dy ₂TiO₅ sensing film annealed at 800 °C exhibited a higher sensitivity (57.59 mV/pH in the solutions from pH 2 to 12), a smaller hysteresis voltage (0.2 mV in the pH loop 7 → 4 → 7 → 10 → 7), and a lower drift rate (0.362 mV/h in the pH 7 buffer solution), presumably because of its thinner low-k interfacial layer at the oxide/Si interface and its higher surface roughness.