Effects of Post-Deposition Annealing and Oxygen Content on the Structural and pH-Sensitive Properties of Thin Nd $_{2}$O $_{3}$ Films

This paper describes the structural properties and sensing characteristics of thin Nd
₂
O
₃
sensing membranes deposited on silicon substrates by means of reactive sputtering. X-ray diffraction, X-ray photoelectron spectroscopy, and atomic-force microscopy were used to study the chemical and morphological features of these films as functions of the growth conditions (argon-to-oxygen flow ratios of 20/5, 15/10 and 10/15; temperatures ranging from 600degC to 800degC). The thin Nd
₂
O
₃
electrolyte-insulator-semiconductor devices prepared under a 15/10 flow ratio with subsequent annealing at 700degC exhibited a higher sensitivity (56.01 mV/pH, in the solutions from pH 2 to 12), a smaller hysteresis voltage (4.7 mV in the pH loop 7 rarr 4 rarr 7rarr 10 rarr 7), and a lower drift rate (0.41 mV/h in the pH 7 buffer solution) than did those prepared at the other conditions. We attribute this behavior to the optimal oxygen content in this oxide film forming a high density of binding sites and a small surface roughness.