Growth behavior and defects in conductive SrRuO 3 thin films grown on a Si(100) substrate by sputtering
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The microstructural characteristics of ion-beam-sputtered conductive SrRuO3 films, such as interfacial reactions, which govern growth behavior, defects, and thermal stability, were investigated using transmission electron microscopy. On a Si substrate, two binary constituents of SrRuO3, i.e., SrO and RuO2 were shown to have quite different reaction behaviors. The reduction of the RuO2 constituent to elemental Ru by Si led to an unstable contact of SrRuO3 on the Si substrate. Possible reaction thermodynamics are suggested, which are based on the formation energies of the corresponding reactions. In the case of films grown in an oxygen-deficient atmosphere, stacking faults were observed. The stacking faults originated from twinning on the {111}pc plane to accommodate the oxygen deficiency in the growth atmosphere by changing the arrangement of RuO6 octahedra from corner to one of face sharing.
I. INTRODUCTION
SrRuO 3 , a metallic conductor (approximately 280 ⍀ cm for single crystals), is structurally compatible with superconducting, ferroelectric, and high dielectric constant materials.1 In fact, SrRuO3 has been employed as an electrode in epitaxially grown single-crystal capacitors and has been shown to have excellent qualities in terms of higher dielectric constants and low leakage current characteristics in BaxSr1−xTiO3 capacitors,2– 6 as well as higher fatigue resistance in ferroelectric capacitors.7–9 Epitaxial SrRuO3 thin films have been successfully grown on a variety of substrates such as SrTiO3,1,7–9 LaAlO3,3,10 MgO with a Pt or BaTiO3 buffer layer,11,12 and Si with a yttria-stabilized zirconia (YSZ) buffer layer.2,13 On the other hand, only several reports have appeared on the microstructural characteristics of conductive SrRuO3 thin films, which have been grown directly on the silicon (Si) substrate.4,5,14,15 When grown at temperatures higher than 500 °C, an SrRuO3 film is polycrystalline in nature with a columnar morphology and has the characteristics of a metallic conductor.14,15 It has been observed that the interface between Si and the SrRuO3 film is susceptible to certain chemical reactions during the growth of the film, resulting in a randomly oriented polycrystalline SrRuO3 film on Si but with rather good lattice matching.5 For this reason a yttria-stabilized zirconia (YSZ) buffered Si substrate is used for the epitaxial growth of SrRuO3 thin films on which YSZ is capable of preventing interfacial reactions between SrRuO3 and Si.2,13 It would be expected that these reaction layers, 1998
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J. Mater. Res., Vol. 16, No. 7, Jul 2001 Downloaded: 15 Jul 2014
without the YSZ buffer layer, could also affect the microstructure as well as the growing lattice planes of the SrRuO3 film, thus leading to a deterioration in the electrical conductivity path between the film and substrate. In addition, since the microstructure of SrRuO3 films plays a decisive role in the structure and electrical properties of capacitor devices, it is important to understand the microstructural natur
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