Preparation of Superconducting Y-Ba-Cu-O Thin Films by Mo-Cvd
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PREPARATION OF SUPERCONDUCTING Y-Ba-Cu-O THIN FILMS BY MO-CVD Hiroshi Ohnishi*, Yoshihiko Kusakabe*, Minoru Kobayashi*, Susumu Hoshinouchi*, Hiroshi Harima** and Kunihide Tachibana** *Manufacturing Development Laboratory, Mitsubishi Electric Corp. Tsukaguchi, Amagasaki, Hyogo, 661, Japan **Department of Electronics, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto, 606, Japan ABSTRACT High-Tc superconducting Y-Ba-Cu-0 films were prepared on MgO(100) substrate by MO-CVD technique without post annealing. The highest Tc obtained was 85K. The film was made up of dense matrix and dispersed fine particles. The Y-Ba-Cu composition of matrix was nearly equal to the 1:2:3 superconducting phase. The film was highly oriented with c-axis perpendicular to the substrate. The lattice constant of the film was 11.68A. INTRODUCTION Future micro-electronic devices will require well-crystallized superconducting films with smooth surface and uniform microstructure. MO-CVD is a potential process for the preparation of such films, because this process has excellent performance in epitaxial growth of GaAs. Recently, some studies were reported for the preparation of oxide superconducting films [1-10], and a few studies succeeded in preparing Y-Ba-Cu-O superconducting films without post annealing [8-101. However, the qualities of these films are not sufficient as for the surface morphology and the microstructure. The comprehensive characterization of the films will be useful to improve the preparation technique for better quality films. In this paper, we report composition and microstructure of the as-grown films in relation to the superconductivity. EXPERIMENT The experimental Y(C 1 1 H1 9 02) 3 , Ba(C
set-up is shown in Fig.1. DPM chelates 02) 2 and Cu(C 1 1 H1 9 0 2 ) 2 were used
1 1 H1 9
REACTOR REACTOR LINE MIXING BLOCK
/VENT
LINE
SUBSTRATE
VACUUM PUMP He 02
-/
CONDUCTANCE VALVE '--HEATER BLOK
L¢ SOURCE TANK
Fig.1 Experimental set-up of MO-CVD Mat. Res. Soc. Symp. Proc. Vol. 169. @1990 Materials Research Society
of as
574
Table 1 Experimental conditions [Y(DPM) Temperature of tank 3(K) Flow rate of He (cm /min)
373 5-15
Flow rate of 02 (cm-/min): 100 Temperature of heater (k):1073 Reacting time (min) 60
Ba(DPM)
453 50
Cu(DPM)
383-388 .. 12.5-50
Pressure of reactor (Pa) : 1300 Substrate MgO(100)
precursors for Y, Ba and Cu elements respectively. They were evaporated in respective source tanks, then mixed and led into a reactor with He carrier gas. The supply of each material was controlled by the temperature of the tank and flow rate of the carrier gas. The 02 was also introduced into the reactor through an isolated gas line. The total gas pressure in the reactor was controlled with a conductance valve before a vacuum pump. Thermal decomposition of precursors and deposition of Y-Ba-Cu-0 film on a MgO(100) substrate were carried out by heating the substrate with a resistance heater block kept at 1073K. After deposition, the substrate was cooled down to room temperature in atmospheric pressure of 02. In T
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