Thermal Conductivity of Amorphous Indium Zinc Oxide Thin Films
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Thermal Conductivity of Amorphous Indium Zinc Oxide Thin Films Ryo Endoh1, Takayuki Hirano1, Masaaki Takeda1 and Manabu Oishi1 Nobuto Oka2 and Yuzo Shigesato2 1 Materials Characterization Laboratories, Toray Research Center, Inc., 3-3-7 Sonoyama,Otsu, Shiga, 520-8567, Japan 2 Graduate School of Science & Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa, 229-8558, Japan
ABSTRACT The thermal conductivity of amorphous indium zinc oxide (IZO) thin films was measured by the 3Ȧ method. Three IZO films were prepared by dc magnetron sputtering method on Si substrate under different O2 flow ratios (O2 / [Ar+O2]) of 0%, 1%, and 5%. The thermal conductivity of IZO films decreases with an increase in O2 flow ratio, the values of the thermal conductivity were 3.4, 3.1 and 1.2 W m-1 K-1 for O2 flow ratios of 0%, 1%, and 5%, respectively. To investigate relationships among the thermal conductivity, the structure and other physical properties, we were carried out nanoindentation, Rutherford back scattering (RBS), electron spin resonance (ESR). The result of ESR measurements indicated that the amount of conduction electron in the IZO film decreases with increasing O2 flow ratio. Increase of O2 flow ratio reduces the amount of oxygen vacancies for providing free electrons. Therefore, decreasing thermal conductivity with an increase in O2 flow ratio is attributed to decreasing conduction electrons as thermal carrier. On the other hand, the chemical composition of IZO films is independent of O2 flow ratio. Furthermore, density, Young’s modulus and hardness also show little changes with increasing O2 flow ratio. Density, Young’s modulus and hardness are strongly associated with the internal structure. It is probable that influence of oxygen vacancies on the internal structure of IZO film is negligibly small. INTRODUCTION Transparent conductive oxide (TCO) films are used for the optoelectronic devices such as liquid crystal displays, solar cells, etc. For these devices, the thermal design is very important technique for cooling and keeping the device below the maximum working temperature. Thermal properties including thermal conductivity are essential factor of the thermal design. However, until now there are only a few reports of the thermal properties of TCO films [1-3]. The purpose of this study is the evaluation of the thermal property for TCO films, especially the thermal conductivity of IZO films. We report the results of the thermal conductivity measurement for IZO films by the 3Ȧ method[4-7]. Though the thermal diffusivity and thermal effusivity measurement such as the thermoreflectance method needs the density and specific heat of the thin film for calculating the thermal conductivity, the 3Ȧ method is able to obtain it directly from the measurement results. In addition, we also report the measurement results of
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nanoindentation, RBS and ESR measurement for IZO films. The correlation of the thermal conductivity with the structure, the composition and other physical properties is discu
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