In-Situ Pulsed Laser Deposition of High-T C Yba 2 Cu 3 O 7 Superconducting Thin Films on (100) LaAlO3 Substrates
- PDF / 1,381,567 Bytes
- 4 Pages / 420.48 x 639 pts Page_size
- 27 Downloads / 180 Views
IN-SITU PULSED LASER DEPOSITION OF HIGH-Tc YBa 2Cu 3 07 SUPERCONDUCTING THIN FILMS ON (100) LaAIO3 SUBSTRATES P. Tiwari, S. Sharan, R. K. Singh, 0. W. Holland* and J. Narayan Department of Materials Science and Engineering North Carolina State University Raleigh, NC 27695-7916 *Solid State Division Oak Ridge National Laboratory OakRidge, TN 37831 ABSTRACT The formation of superconducting thin films on lanthanum aluminate substrates is very important for high-frequency applications. In this paper, we discuss the fabrication of epitaxial superconducting YBa 2Cu 3O 7 thin films on (100)LaA10 3 substrates, which exhibit excellent dielectric properties required for high frequency applications. The films were deposited by the biased pulsed laser evaporation technique (PLE) at substrate temperatures between 500-650'C and exhibit excellent crystallinity with best minimum ion channeling yields corresponding to approximately 3%. The superconducting transition temperatures varied from 88-92 K with critical current densities at 77K and zero magnetic field greater than 4 - 5 x 106 Amps/cm 2. INTRODUCTION The best quality YBa 2Cu 3O7 thin films exhibiting excellent superconducting properties have been reported on (100) SrTiO 3 substrates[l]. However, strontium titanate substrates are unsuitable for microwave applications because of their poor dielectric properties with a dielectric constant of nearly 307 at low frequencies [2,3]. In contrast, LaA103 substrates possess excellent dielectric properties with a dielectric constant of approximately 15 for low frequencies and 17 for high frequencies (53 GHz). In addition, the crystal structure is nearly cubic with a lattice parameter of 3.7904± 0.0010 which corresponds to a lattice mismatch of nearly 0.9% and 2.5% with 'a' and 'b' lattice parameter of YBa 2 Cu 30 7 , respectively. Thus lanthanum aluminate substrate presents itself as an excellent quality substrate for microwave applications. In this paper, we report the formation of excellent quality epitaxial superconducting thin films on (100) LaA10 3 substrates by the pulsed laser evaporation technique in the temperature range of 500-650'C [4,6]. In the lower temperature a positively biased interposing ring was found to improve the thin film superconducting properties. The films exhibit very high degree of crystallinity with minimum ion channeling 2 yields corresponding to ideal values and critical current densities of over 4 - 5 x 106 Amps/cm for films deposited at 600'C. EXPERIMENTAL In the experimental setup for PLE deposition of superconducting thin films, a pulsed excimer laser is directed on to a bulk target possessing a stoichiometric 1-2-3 composition and the deposited material is collected on a substrate placed at a distance of about 3-5 cm away from the target. The oxygen partial pressure in the chamber is between 180-200 mtorr with the oxygen jet directed towards the substrate. For biased deposition, a positively biased ring is placed near the target with a potential of +300-400V. During the deposition process, the beam i
Data Loading...
