Structural properties and sensing characteristics of high-κ Eu₂O₃ film for electrolyte-insulator- semiconductor pH sensors

In this study, we report the effect of thermal annealing on the structural properties and sensing characteristics of Eu₂O₃ sensing membrane deposited on Si substrates through reactive sputtering for electrolyte-insulatorsemiconductor (EIS) pH sensors. X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy revealed the structural, morphological, and chemical features, respectively, of Eu₂O₃ films after they had been subjected to annealing at various temperatures (700, 800, and 900 °C). The Eu₂O₃ EIS device annealed at 900 °C exhibited a higher sensitivity of 58.65 mV/pH, a lower hysteresis voltage of 1 mV, and a smaller drift rate of 0.38 mV/h than did those prepared at the other annealing temperatures. We attribute this behavior to an increase of the amount of oxygen sites improving the stoichiometry of Eu₂O₃ film and its surface roughness.