Interfacial effect on thermal conductivity of Y2O3 thin films deposited on Al2O3

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Abstract

The interfacial effect on thermal conductivity is studied with Y2O3 thin films deposited on an Al2O3 substrate. Y2O3 thin films with the thickness between 100 and 500 nm are prepared using rf magnetron sputtering and thermal conductivity of the films is measured using the 3ω method. The strong film thickness-dependent thermal conductivity due to the interfacial thermal resistance is observed. The film thickness-dependent thermal conductivity is explained by an interface thermal resistance between the film and substrate.

Introduction

Yttrium oxide (Y2O3) is a suitable material for a metal/insulator/semiconductor structure due to its particular physical properties such as a high dielectric constant (12–18), a wide band gap energy (5.5 eV), and high thermal stability up to 2300 °C [1]. The interfacial effect becomes more important in determining the physical properties as the system size decreases [2]. There have been reports on the reduced thermal conductivity of dielectric material consisting of nano-sized grains and films [3], [4], [5]. Nanocrystalline yttria-stabilized zirconia (YSZ) showed the strongly grain size-dependent thermal conductivity at temperatures between 6 and 480 K and the interfacial thermal resistance of grain boundaries was determined with the measured grain size-dependent thermal conductivity of YSZ [3]. Yamane et al. [4] reported the film thickness-dependent thermal conductivity of SiO2 thin films deposited on Si and obtained the interfacial thermal resistance of SiO2/Si from the film thickness-dependent thermal conductivity. As the technology to produce miniature devices has developed rapidly, the interfacial effect becomes more important. While Y2O3 has been considered as a suitable material for a metal/insulator/semiconductor structure, no much work about the interfacial effect on thermal conductivity of Y2O3 thin films has been performed. This work focuses on the interfacial effect on thermal conductivity of thin films.

In this study, the interfacial effect on thermal conductivity is studied with Y2O3 thin films deposited on Al2O3 substrates. Y2O3 thin films with thickness between 100 and 500 nm are prepared on Al2O3 substrates using rf magnetron sputtering. The optimized conditions for the growth of Y2O3 thin films are determined as varying the rf power, substrate temperature, post-annealing temperature, and deposition time. Thermal conductivity of Y2O3 films was measured using the 3ω method and the film thickness-dependent thermal conductivity is understood with the interfacial thermal resistance.

Section snippets

Experimental details

Y2O3 films are deposited on Al2O3 substrates using rf magnetron sputtering. The source material is a Y2O3 ceramic target of 2 in. diameter and 0.25 in. thickness with 99.99% purity. During the deposition, the substrate is heated and rotated with 3 rpm for the uniform film growth. Y2O3 films are grown as varying the rf power, substrate temperature, gas pressure, post-annealing temperature, and deposition time. The film structures are analyzed with an X-ray diffraction (XRD: Rigaku GDX-11P3A)

Results and discussion

It is found from the measurement of the film thickness with SEM that the film thickness increases linearly with a deposition time, which gives the deposition rate, 3.05 nm/min. The film thickness can be controlled as varying the deposition time. Fig. 1 shows the cross-sectional and surface SEM images of a 360 nm thick Y2O3 films after post-annealing at 800 °C for 2 h.

Fig. 2 shows the XRD patterns of 120, 200, 360, and 500 nm thick Y2O3 films grown for 25, 50, 100, and 150 min, respectively. The main

Conclusion

Y2O3 films are deposited on Al2O3 substrates using rf magnetron sputtering as varying the film thickness between 100 and 500 nm. The film thickness, structures, and surface conditions are analyzed with XRD patterns and SEM images. Thermal conductivity of Y2O3 thin films is measured with the 3ω method.

Y2O3 thin films on Al2O3 substrate exhibit the apparent film thickness-dependent thermal conductivity. As the thickness of Y2O3 thin films decreases, thermal conductivity of Y2O3 films is reduced

Acknowledgements

This work was supported by Korean Research Foundation Grant, KRF-2003-015-C00227, and grant No. RTI04-02-01 from the Regional Technology Innovation Program of the Ministry of Commerce, Industry and Energy, Korea.

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