Effects of ceramic-film thickness on humidity sensitivity of Al/Ba1-xLaxNbyTi1-yO3/SiO 2/Si structure

Abstract

Using the argon ion-beam sputtering technique, 0.5, 1 or 2 μm of Ba1-xLaxNbyTi1-yO3 (x = 0.25%, y = 0.25%) film was deposited on a SiO2/Si substrate to make metal-insulator-semiconductor capacitors. The dependence of the humidity sensitivity of the device on the film thickness was studied. The sensor with the 0.5 μm film was nine times more sensitive than that with the 2 μm film. The results are explained by the porosity and pore-volume distribution of the films, which were extracted from the device capacitance at different relative humidities based on a physical model. The thinner the thin film, the higher was the porosity, and thus the higher was the sensitivity of the device to humidity. Compared with the porosity, the pore-volume distribution hardly affected the humidity sensitivity because the fractions of pores with radii smaller than 50 Å were almost the same (∼70%) for the three film thicknesses.