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 Dy2O3 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 Dy2TiO5 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.