Electrical Properties Of Indium Tin Oxide Thin Films Prepared By Electron Beam Evaporation

Indium tin oxide (ITO) has been widely used as a transparent conductive film in solar cells, liquid crystal displays and other optoelectronic devices, owing to its high transmittance of visible light and relatively low resistivity. However, the study of its piezoresistive effect is quite rare. As a candidate for the active strain elements in high-temperature environment, it has received some attention abroad and new researches are being carried out. The purpose of this article is to study its electrical property by measuring the piezoresistive effect, which is characterized by a gauge factor (G), and the temperature coefficient of resistance (TCR).The indium tin oxide films were prepared by electron beam evaporation on glass substrates and its chemical composition, crystal structure and optical properties were characterized by routine procedures. The effect of post-deposition annealing process on its property was also studied. And then, photolithography and wet etching were used to pattern the ITO films for electrical measurement, which involved the measurement of temperature coefficient of resistance and the gauge factor. The former was obtained by changing the temperature of the film through blackbody radiation and measured the resistance under different temperatures. A model was established to fit the resistance-temperature curve during the temperature decreasing stage. The temperature coefficient of resistance and activation energy of the carriers was obtained from the fitting parameters. The latter experiment was carried out at room temperature. By changing the displacement at one end of the ITO sample, the gauge factor could be calculated from the resistance change with the different strains. Since the resistance of the ITO samples had a drift during the measurement process which can not be ignored, this had to be included in all the calculations. The effect of joule heating on the resistance change due to the test current was also estimated and proved to be negligible compared with that due to piezoresistivity. The gauge factors of the ITO samples were measured under the tensile strain and compressive strain as well, a consistent gauge factor of -2.1 was obtained.