Characterization on pH sensing performance and structural properties of gadolinium oxide post-treated by nitrogen rapid thermal annealing

A detail investigation on the pH sensing performance of Gd ₂O₃ layer was proposed in this work. Electrolyte- insulator-semiconductor (EIS) structure with Gd₂O₃ layer deposited directly on silicon by reactive radio frequency sputtering with Gd target was chosen as the testing platform. The postdeposition rapid thermal annealing (RTA), performed at various temperatures for 1 min in N₂ ambience, was first used to improve the pH sensing performance of Gd ₂O₃. With RTA treatment at 800°C, pH sensitivity of Gd₂O₃ EIS structure can be increased from 35.5mV/pH to 55 mV/pH. This behavior can be explained by the increase of surface sites, which is supported by atomic force microscopy analysis. With RTA treatment at 700°C and 800°C, the drift coefficient for Gd₂O₃ layer was reduced to 0.03 and 1.2mV/h, which is resulted from the densification of Gd ₂O₃ layer supported by x-ray photoemission spectrometry. Therefore, Gd₂O₃ layer with RTA in N₂ ambience at 700°C or 800°C could be a potential candidate for pH-sensitive membrane.