In-Situ Patterning and Critical Current Density Measurements in Laser Deposited High-Tc Superconducting Thin Films
- PDF / 519,166 Bytes
- 4 Pages / 420.48 x 639 pts Page_size
- 107 Downloads / 246 Views
IN-SITU PATTERNING AND CRITICAL CURRENT DENSITY MEASUREMENTS IN LASER DEPOSITED HIGH.Tc SUPERCONDUCTING THIN FILMS R. K. Singh, C. B. Lee, P. Tiwari and J. Narayan
Department of Materials Science and Engineering North Carolina State University Raleigh NC 27695-7916 ABSTRACT
We have performed transport critical current density, Jc, measurements on epitaxial superconducting thin films which were in-situ patterned during the laser deposition process. Shadow masks of various dimensions were placed close to the substrate to generate different patterns. Epitaxial films of YBa 2Cu3 0 7 on (100) SrTiO 3 , (100) YSZ, and (100) LaAIO 3 substrates were fabricated at low processing temperatures (500-6501C) by the biased laser deposition technique in an oxygen ambient of 200 mtorr. Excellent quality superconducting thin films were formed on patterned areas. The critical temperature of the films was found to be in the range of 88 to 6 90 K, and the best critical current density values (at 77K, and zero magnetic field) greater than 6.5 x10 Amps/cm2 were obtained for silver doped YBa 2Cu3 0 7 films on (100)LaAIO 3 substrates. INTRODUCTION Epitaxial YBa 2Cu3 0 7 thin films with excellent superconducting properties have been prepared in-situ by the pulsed laser deposition technique[I-2] at temperatures in the range of 550 to 650'C in an oxygen ambient. The processing temperatures can be further reduced to 500*C by incorporation of a biased ring between the substrate and the target. As YBa2 Cu307 possesses short anisotropic coherence lengths (-15-25 Aalong a- and b-axes and -5A along its c-axis), defects like grain boundaries with widths 5-10A may affect the intergrain critical current density without affecting the intragrain critical current density in polycrystalline specimens. The measurement of the transport critical current involves patterning of the film by many different techniques including ion implantation, lift-off method, laser evaporation or wet etching[3-5]. We have developed a simple in-situ patterning method which does not require any post processing steps [6]. This method involves placement of a thin patterned steel plate (shadow making) above the substrate. Above a certain transverse dimensions of the mask, the microstructural and superconducting properties have been found to be the same for both patterned and unpatterned areas. EXPERIMENTAL
A pulsed excimer laser (2 =308 nm, r =45 ns) with energy density in the range of 2 to 2.5 J/cm 2 is employed to ablate a bulk 123 target and the evaporated material is deposited on a substrate maintained in the temperature range of 500 to 6500C in a 200 mtorr oxygen ambient [2]. In the lower temperature regime the use of a positively biased ring between the substrate and the target was found to lead to a marked improvement in the superconducting and the microstructural properties. A polished steel plate suitably patterned was placed on the substrate. The incorporation of oxygen from the jet into the film was not affected by the presence of the steel mask probably as a result o
Data Loading...
