Influence of oxygen content and post-deposition annealing on structural and sensing characteristics of Tm₂o₃ thin membranes for ph detection

In this paper, we describe an electrolyteinsulatorsemiconductor (EIS) device prepared from Tm₂o₃sensing membranes deposited on Si (100) substrates through 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 10/20, 15/15, and 20/10; temperatures ranging from 700 to 900°C The Tm₂o₃ EIS prepared under an Ar/O₂ flow ratio of 15/15 with subsequent annealing at 800°C exhibited a higher sensitivity (58.02 m^V/pH, in the solutions from pH 2 to 12), a smaller hysteresis voltage (2 mV in the p ^H loop 7→ 4→ 7→ 10→ 7), and a lower drift rate (1.04 mV/h in the pH 7 buffer solution) than those of the other conditions. We attribute this behavior to the optimal oxygen content in this oxide film forming a strong (622) crystallographic orientation of Tm₂o₃, a thin low-k interfacial layer, and a large surface roughness.