Properties of Ta205 Gel Thin Films Prepared by the Drop-Coating Methodt

Abstract

Coating sol solutions were prepared from anhydrous ethanol solutions of Ta(0C2H5)5. With the addition of high-purity acetic acid, Ta(0C21-15)5 was partially hydrolyzed by trace amounts of water in the acetic acid used and further condensation took place. Among the sol solutions obtained, the solution (A) containing 1.2 mol% Ta(OC21-15)5 together w ith acetic acid at its molar ratio of 1.5 to Ta(0C2H5)5 was transparent and stable on storage for two months. When chelating agents (diethyl malonate, acetylacetone, ethyl acetoacetate and ethyl acetate) were added to one of the starting solutions, the agents (especially diethyl malonate)were found to remain in gels when the solution was dried at room temperature. Among these gels, one containing acetylacetone crystallized at the highest temperature of about 830 °C on heating. Ta205 gel thin films were prepared from the solution (A) by the drop-coating method, the solution was dropped on a substrate to spread over and evaporate. Preparation under dry nitrogen (-0% relative humidity) gave a transparent gel film at room temperature. DTA analysis revealed that, on heating in air, the gel film crystallized around 840 °C which was higher by about 100 °C than the crystallization temperatures of the other gels prepared under high relative humidities. On heating under nitrogen atmosphere, the exothermic peak of crystallization at 840 °C decreased extremely to be replaced by a weak exothermic peak (appearing) at 1000 °C. Preparation test under different relative humidities and substrate temperatares showed that transparent gel films were obtained regardless of substrate ternpetatures under low relative humidities, while only at somewhat elevated substrate temperatures under high humidities. t Properties of T a 205Thin Films Prepared by the Sol-Gel Process. I.