Fabrication of SrRuO 3 Epitaxial Thin Films on YBa 2 Cu 3 O x / CeO 2 / YSZ - Buffered Si Substrates by Pulsed Laser Dep
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Fabrication of SrRuO3 Epitaxial Thin Films on YBa2Cu3Ox / CeO2 / YSZ – Buffered Si Substrates by Pulsed Laser Deposition Takamitsu Higuchi, Koichi Morozumi, Setsuya Iwashita, Masaya Ishida and Tatsuya Shimoda Technology Platform Research Center, SEIKO EPSON Corporation 281 Fujimi, Fujimi-machi, Nagano 399-0293, Japan ABSTRACT Pseudocubic SrRuO3 (100) epitaxial thin films were fabricated on Si (100) with a YBa2Cu3Ox / CeO2 / YSZ (yttria-stabilized-zirconia) triple buffer layer ∼ 14 nm thick by pulsed laser deposition (PLD). Reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) revealed that the first buffer layer of YSZ (100) was epitaxially grown on naturally oxidized Si (100) substrates with the process condition of PB (base pressure) = 1×10-6 Torr, PO2 (oxygen partial pressure) = 5×10-5 Torr, and Ts (substrate temperature) = 700 °C. Higher deposition rate of YSZ in the range of 0 ∼ 0.6 nm/min brought about better crystallinity with a smaller value of a full-width at half maximum (FWHM) in the YSZ (200) rocking curve. Subsequent deposition of CeO2, YBa2Cu3Ox, and SrRuO3 resulted in an SrRuO3 (100) epitaxial thin film exhibiting good crystallinity with FWHM = 1.7° in the SrRuO3 (200) rocking curve. INTRODUCTION SrRuO3 has attracted much attention as a perovskite-type oxide electrode material for electronic devices. SrRuO3, possessing a GdFeO3-type orthorhombic structure with lattice parameters of a = 5.5670 Å, b = 5.5304 Å, and c = 7.8446 Å [1] (a = 3.9231 Å in a pseudocubic structure), is also utilized as a seed layer for heteroepitaxial growth of other perovskite oxides. Particularly for ferroelectric devices using perovskite oxides such as Pb(ZrxTi1-x)O3, heteroepitaxial growth can enhance spontaneous polarization or remanent polarization with good alignment of the polarization axis, or with large strain of the crystal lattice [2]. Although it is easy to form SrRuO3 (100) epitaxial thin films on perovskite-type single crystal substrates such as SrTiO3 (100) (a = 3.908 Å), it is difficult to fabricate SrRuO3 (100) epitaxial thin films directly on Si substrates, since an amorphous SiO2 layer is easily formed on the Si surface during the deposition of perovskite-type oxides [3]. Therefore, a metal oxide buffer layer which is thermodynamically stable in contact with Si [4] is needed. For example, MgO (a = 4.211 Å) or SrO (a = 5.140 Å), which has a rock salt-type cubic structure, has been employed as a buffer layer material. MgO is epitaxially grown on Si with an orientation relationship of MgO (100) / Si (100) [5]. Owing to a large lattice mismatch of -22.5% with Si (a = 5.431 Å), however, two different in-plane orientation relationships of MgO // Si and MgO // Si co-exist [6]. SrO is also epitaxially grown on Si. However, relatively low PB (< 1×10-6 Torr) is necessary for the epitaxial growth, which is not desirable for industrial processes [7,8] On the other hand, YSZ (a = 5.17 Å), which has a fluorite-type cubic structure, is also thermodynamically stable in contact with Si [4] an
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