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A new multi-function microsensor with a barium lanthanum titanate (Ba1-xLaxTiO3) thin film is developed for the fabrication of a thin-film resistor and a metal-insulator-semiconductor (MIS) capacitor on a SiO2/Si substrate. The results reveal that the thin-film resistor has good sensitivity to visible light and good thermal sensitivity within the temperature range of 28-400 °C. The MIS capacitor is sensitive to changes in the relative humidity (RH), with a 130% change of the current for a humidity change from 12 to 92% RH at a test frequency of 500 Hz, and with short response times of 5 and 4.5 s for the adsorption and desorption of water vapor, respectively. The effects of the test frequency on the photo, thermal and humidity sensitivity performances are also investigated. Since the lifetime of charge carriers of Ba1-xLaxTiO3 thin films is only 16 ms, about half that of Sr1-xLaxTiO3 thin films, the device can detect light modulation at higher frequencies.

Using the argon ion-beam sputtering technique, 0.5, 1 or 2 µm of Ba 1−x La x Nb y Ti 1−y O 3 (x = 0.25%, y = 0.25%) film was deposited on a SiO 2 /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.

The optical characteristics of barium-strontium titanate-niobate (Ba 1−x Sr x Nb y Ti 1−y O 3 ) thin-film resistor are investigated and the effects of annealing gas and annealing temperature on photoelectrical properties are studied. Experimental results show that Ba 1−x Sr x Nb y Ti 1−y O 3 thin films are highly sensitive not only to visible light, but also to ultraviolet light. As compared to N 2 -annealed devices, O 2 -annealed devices have higher photosensitivity and lower dark current. Moreover, the photosensitivity of the O 2 -annealed devices is reduced for higher annealing temperature. Based on scanning electron microscope (SEM) study and grain-boundary theory, it can be concluded that 400 • C in O 2 is the optimal annealing condition, which can give a photosensitivity as high as 8400% to visible light and 5500% to ultraviolet light.