Characterization of sputtered iridium dioxide thin films
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Characterization of sputtered iridium dioxide thin films P. C. Liao, W. S. Ho, and Y. S. Huanga) Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan, Republic of China
K. K. Tiong Department of Electrical Engineering, National Taiwan Ocean University, Keelung 202, Taiwan, Republic of China (Received 9 December 1996; accepted 16 January 1998)
Iridium dioxide (IrO2 ) thin films, deposited on Si substrates by reactive rf sputtering method under various conditions, were characterized by atomic force microscopy (AFM), x-ray diffraction (XRD), electrical-conductivity, spectrophotometry, ellipsometry and Raman scattering measurements. The average grain sizes of the films were estimated by AFM. A grain boundary scattering model was used to fit the relation between the average grain size and electrical resistivity. The optical and dielectric constants were determined by the ellipsometry measurements. The results of the electrical and optical studies show a metallic character of the films deposited at higher temperatures. The results of XRD and Raman scattering indicate that the IrO2 films deposited at temperatures higher than 300 ±C show the presence of (200) texture.
I. INTRODUCTION
Iridium dioxide, IrO2 , is one of a few naturally highly conductive stoichiometric oxides1 ; the oxides have bulk resistivities at room temperature ranging from 30 to 100 mV-cm and are corrosion resistant.2 In recent years, much attention had been paid to the investigation of sputtered iridium oxide films (SIROF’s) for their potential technological applications in the oxygen and chlorine evolution anodes,3–6 electrochromic displays,7,8 pH sensors,9–12 electrodes for neural stimulation,13,14 and the capacitor of nonvolatile memories and dynamic random access memories.15,16 The properties of the IrO2 films employed in any of these applications will be sensitive to the structure of the films, which will be influenced by the methods and the conditions of film preparation. SIROF’s deposited at temperatures T > 130 ±C are found to be polycrystalline,17 while those deposited at T , 100 ±C are amorphous or microcrystalline. Amorphous SIROF’s had been found to be considerably hydrated due to the residual water vapor in the reactor chamber, and it had been reported that some of the impurities such as O2 , H2 , H2 O, and Ar present in the film can be eliminated by heating in vacuum. Moreover, an exothermic phase transition at about 300 ±C transforms the amorphous material into a polycrystalline form.18 The high-temperature behavior of SIROF’s is important for applications in pH sensors, microelectronic devices, etc. However, very few information about the
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http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 5, May 1998
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solid state properties of SIROF’s can be found in the literature. In this article we report a detailed characterization of the solid s
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