A Highly pH-Sensitive Eelectrolyte Insulator Semi-conductor Element Using A Stack of Anodic Gd Oxide/Silicon Oxide

In this paper, the Gd₂O₃/SiO₂ stacks were fabricated in an anodic oxidation method and used as a pH-sensitive electrolyte insulator semiconductor (EIS) element for pH value test. Several outstanding results are obtained, they are: (1) The higher pH-value solution the EIS samples were immersed in, the more rugged surface the films were observed. (2) The etched thickness of the Gd₂O₃ layer almost linearly increases with the decrease of pH value. (3) The C-V curves for EIS samples etched with decedent pH- value solutions were shifted to right in a ratio around 56.72 mV/pH. (4) When fixing in the same capacitance, the linear factor of the voltage compared with a fitting linear curve is 99.98%, which is much closed to ideal case. From those results, the Gd₂O₃ oxide can be adequately regarded as a pH-sensitive EIS device for the bio-medicine test of the human blood, urine and even saliva, of which pH-values may be changed by different syndromes of diseases.