Room-temperature preparation of biaxially textured indium tin oxide thin films with ion-beam-assisted deposition
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Jörg Hoffmann Zentrum für Funktionswerkstoffe gGmbH, Windausweg 2, 37073 Göttingen, Germany
Herbert C. Freyhardt Institut für Materialphysik, Windausweg 2, 37073 Göttingen, Germany, and Zentrum für Funktionswerkstoffe gGmbH, Windausweg 2, 37073 Göttingen, Germany (Received 25 July 2002; accepted 18 November 2002)
Biaxially aligned indium tin oxide (ITO) thin films were prepared by an ion-beamassisted deposition (IBAD) process at room temperature. Films with a transmittance at 550 nm of 90% and an electrical resistivity of 1.1 × 10−3 ⍀cm for 300 and 250 nm thickness were obtained. Investigations of the texture evolution during IBAD film growth were carried out and compared to the well-established texture development in yttria-stabilized zirconia. An in-plane texture of 12.6° full width at half-maximum (FWHM) for a 1-m-thick IBAD-ITO film was achieved. The quality of these films as electrically conductive buffer layers for YBa2Cu3O7−␦ (YBCO) high-temperature superconductors was demonstrated by the subsequent deposition of high-current carrying YBCO films by thermal co-evaporation using a 3–5-nm-thick Y2O3 interlayer. A JC of 0.76 MA/cm2 (77K, 0 T) was obtained for a 1 × 1 cm sample with ITO of 20° FWHM.
I. INTRODUCTION
The deposition of indium tin oxide (ITO) as a transparent conducting oxide used for transparent electrodes in form of polycrystalline films in semiconductor technology has been widely studied, mainly on glass surfaces.1,2 For optimum resistivity values (approximately 10 −4 ⍀cm) and transmittance in the visible range (>85%), the deposition conditions, such as oxygen pressure, deposition rate and temperature, must be carefully chosen. The typical deposition/annealing temperature is about 300 °C. At low temperatures, i.e., lower than 100 °C, it was not possible to obtain crystalline films with good properties. For many applications, which, for example, require a deposition on organic materials, such low deposition temperatures are desirable. Currently, low-temperature deposition techniques are under investigation, e.g., an ion-beam-assisted deposition (IBAD) technique that allows good optical and electrical properties by room temperature (RT) deposition.3,4 The crystallinity of these films is not reported. The impact of ions with moderate high energies (greater than about 100 eV) on the growing film during an IBAD process is well known to improve the crystallinity and to force a pronounced texture perpendicular to the film surface. Frequently, a grain alignment is also observed in the film plane. These so-called biaxially 442
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J. Mater. Res., Vol. 18, No. 2, Feb 2003 Downloaded: 14 Mar 2015
textured films reveal a reduced number of large-angle grain boundaries, which might affect the optical and electrical properties of transparent conductive oxides like ITO. Conductive thin films also may be of strong interest for high-temperature superconducting (HTSC) applications. If they can be grown with a biaxial texture, they are of current interest as a template for HTSC deposit
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