Transmission electron microscopy study of the structure of radio frequency sputter-deposited yttria-stabilized zirconia
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Brian R. Stoner Curriculum in Applied and Materials Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 2759, and Materials and Electronic Technologies Division, MCNC, Research Triangle Park (RTP), North Carolina 27709
Jeffrey Y. Thompsona) Curriculum in Applied and Materials Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, and Department of Operative Dentistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599 (Received 10 September 2002; accepted 24 October 2002)
Transmission electron microscopy (TEM) was used to investigate the structural properties of sputter-deposited yttria-stabilized zirconia (YSZ) thin films. YSZ films were deposited over a range of temperatures and background oxygen levels. Additionally, a multilayered structure was produced by cyclic application of a substrate bias. Plan-view TEM showed that temperature and oxygen levels did not have a significant effect on grain size but did alter the phases present in the thin films. Cross-sectional TEM showed the development of texture in the multilayer film, both within the individual layers and in the entire film.
I. INTRODUCTION
Yttria-stabilized zirconia (YSZ) thin films exhibit a number of properties (e.g., high refractive index, low thermal conductivity, good corrosion resistance) that make them useful in a number of applications. Particular interest in YSZ revolves around its use as a buffer layer in superconducting films1,2 and in the development of thermal barrier coatings.3,4 Given their high fracture toughness and strength, zirconia thin films may also be useful in applications where a film with good mechanical properties is required, such as wear-resistant coatings or the modification of brittle substrate materials. Zirconia-based thin films can be deposited by an assortment of techniques, including plasma spraying,5 electron beam evaporation,6 radio frequency (rf) and direct current sputtering,7 chemical vapor deposition,8 laser ablation,9 and ion-beam sputtering.10 The microstructure and properties of a YSZ film are strongly dependent on the deposition method and parameters. Two studies by Ji et al. examined the effect of biassputtering on zirconia thin films.11,12 The first study examined zirconia doped with 2 and 4.5 mol% yttria. In a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 1, Jan 2003
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both cases, the films deposited with bias showed a very strong preference for the (111) orientation, while those grown with no bias were randomly oriented. The second study involving zirconia used undoped ZrO2. Substrate biases of −100 and −400 V both caused the formation of tetragonal zirconia; however the lower bias showed a strong (200) preference, while the higher bias showed the (111) preference seen for doped films. The texturing effect is common for thin films of other materials grown under a substrate bias. One stud
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