In Situ Preparation of Y-Ba-Cu-O Thin Films on Silicon Single Crystals
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IN SITU PREPARATION OF Y-Ba--Cu--O THIN FILMS ON SILICON SINGLE CRYSTALS Hanns-Ulrich Habermeier, Gunter Wagner, and Giinter Mertens Max-Planck-Institut fuir Festk6rperforschung, Heisenbergstr.1, Federal Republic of Germany
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Stuttgart,
ABSTRACT Superconducting Y-Ba--Cu-O thin films with critical temperatures exceeding 80 K are deposited on silicon single crystal substrates using the pulsed laser deposition technique. Deposition from a sintered Y1 Ba 2 Cu 3 0 7 target in oxygen ambient of 0.1 - 5 mbar onto substrates kept at 700°C to 820°C results in crystalline films in which the target composition of the metallic constituents is preserved. No post deposition treatments are required to obtain high values for the zero resistance. X- ray analysis as well as Raman spectroscopy reveal that specimens prepared at optimum conditions are single phase c-axis oriented. In contrast to films prepared on LaA10 3 or SrTiO 3 the surface morphology shows a granular structure. The films prepared by this technique are quite stable against chemicals used in conventional lithographic patterning, however, a strong correlation between film quality before patterning and some degradation after patterning is observed.
INTRODUCTION The development of an advanced preparation technology for high temperature superconductor (H-TS) thin films, e.g. Y- Ba--Cu--O,opens the possibility of their practical implementation into the area of microelectronics. Devices based on Josephson junctions,passive interconnects in conventional circuitry,semiconductor devices combined with UTS elements using the considerable potential of the electrical and optical properties of HTS materials are some of the applications envisaged in the near future. However, these films have been sucessfully deposited with good superconducting properties only on insulating substrates like SrTiO 3 ,MgO, ZrO 2 and LaAIO 3 . The deposition on semiconductor substrates, e.g. silicon, yielded much poorer results [1,2,3] and no superconductivity is observed if preparation schemes are applied combining low temperature deposition with ex--situ furnace annealing. Basically, the problem of low quality HTS films on silicon arises from the interaction of film species with the substrate at high temperatures required for crystallization of the oxides in the superconducting phase. To reduce this diffusive interaction a variety of buffer layers such as 5iO2 , ZrO2 or MgO have been used and films with Tc'S up to 80 K have been reported [ 4 1. The direct depostion of Y-Ba--Cu--O on silicon has been proven to be successful if the material is deposited on substrates at temperatures,Td,exceeding 6000C where the tetragonal crystalline phase is formed immediately [ 5,6 ]. In this so called in--situ scheme the first layers of the deposit will act as a naturally grown diffusion barrier. These films not only have a high value of Tc, they are also relatively stable and can be patterned using conventional lithography [ 7 ]. In this paper we report the development of a preparation scheme for Y-Ba--Cu--
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