Preparation of transparent conductive RuO2 thin film from its precursor solution

It has been reported that RuO2 has a conductive nature like common metals despite its metal oxide character and has widely been used as a coating material for electric resistors etc. However, so far no report concerning the preparation of a transparent film has been found in the literature. We continued the efforts to prepare a transparent RuO2 film and developed a new method different from the conventional sol-gel method by preparing the precursor in a n-butanol-benzene system. To analyze the process of crystallization, the thermal behavior of RuO2, gel formed initially and the gases evolved during heat-treatment of the gel were investigated by TG-DTA-MS. The structure of the thin films after heat-treatment at 100, 250, and 450degreesC was measured by the X-ray diffraction method. n-Butanol and water were observed to evolve at a temperature range of 100-180degreesC beyond their boiling points. Transformation from the gel phase to the crystalline phase occurred at a temperature range of 100-250degreesC without any observation of the heat of crystallization upon DTA analysis. These results suggest the formation of an ordered gel network structure, which seems to arise from arrangement by the interaction among RuO2, precursors having both butoxy (hydrophobic) and hydroxy (hydrophilic) groups. Furthermore, it was presumed that the RuO2 gel crystallizes through the dehydration and dealcoholization reactions among these RuO2 precursors. The RuO2 thin films with thicknesses of 7.0 and 23.8 nm after heat-treatment at 450degreesC have transmittances of 59.6-75.8%, 36.2-59.0% in the wavelength range 380-780 nm, and electrical resistivities of 9.60 X 10(-4) and 4.15 x 10(-4) Omegacm, respectively. These thin films showed sufficient adhesion to a glass substrate.