Fabrication of YBa2Cu3O7-δ film by laser chemical vapor deposition using Ba(hfa)2ṡtetraglyme

PHYSICA(~

Physica C 235-240 (1994)577-578 North-Holland

Fabrication of YBa2Cu307-5 Film by Laser Chemical Vapor Deposition using Ba(hfa)2.tetraglyme Yasuyuki MIZUSHIMA, and Izumi HIRABAYASHI

Superconductivity Research Laboratory, ISTEC, 2-4-1 Mutsuno, Atsuta-ku, Nagoya 456, JAPAN Superconducting oxide films of YBa2Cu307-8 (YBCO) were produced on magnesia (MgO) and strontium titanate (STO) single crystal substrates (100) by laser metalorganic chemical vapor deposition. Ba(hfa)2.tetraglyme was used as a Ba source metalorganic material. When KrF laser was irradiated during deposition, smoother surface of YBCO film was obtained compared to that without irradiation. YBCO film prepared at 750 °C on the MgO substrate showed 69 K of Tc, and Tc became 85 K with KrF laser irradiation. 1.

INTRODUCTION

High-Tc superconducting oxide thin films have been studied by metal organic chemical vapor deposition (MOCVD). However, there are some problems in YBa2Cu307-8 (YBCO) film produced by MOCVD, such as deviation of composition ratio of YBCO because of instability of MO sources. Especially, Ba MO source used to be kept high temperature because of low vapor pressure compared with Y or Cu MO sources. Recently, a novel Ba source which has high volatility and stability against water had been developed [1]. YBCO film was prepared using this Ba source [2]. The authors have studied the YBCO film prepared with laser assisted MOCVD. In this study, YBCO film was prepared with laser MOCVD using this Ba source and effects of laser were investigated. 2.

EXPERIMENTAL

Table 1 lists the condition of deposition. The source materials were ~-diketone of tris (dipivaloyl-methanato) yttrium (Y(DPM)3), copper (Cu(DPM)2), and Ba(hfa)2.tetraglyme (hfa = 1,1,1,5,5,5-hexafluoro-2,4pentanedionate, tetraglyme = 2,5,8,11,14pentaoxapentadecane). The mixture of the source materials with argon carrier gas was introduced into the reactor through the pipe inlet. The oxygen gas was separately

introduced into the reactor. MgO and STO (100) single crystal substrate (10x10x0.5 mm 3) was used for a substrate. The substrate was heated by a ceramic heater. KrF excimer laser (248 nm) was introduced into the reactor through a window and irradiated on the substrate directly during the deposition. The crystalline phase of the films was determined by the X-ray diffraction (XRD) pattern. The decomposition of the source materials was observed by the UV spectroscopy. The surface morphology was observed by a scanning electron microscope (SEM) and atomic force microscope (AFM). Table 1 Conditions of deposition with laser MOCVD Evaporator temperature (°C) Y(DPM)3 Ba(hfa)2.tetraglyme Cu(DPM)2 Deposition temperature 02 gas flow rate Deposition time Total pressure KrF laser Intensity Repetition rate

0921-4534/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved. SSDI 0921-4534(94)00850-7

112 °C 111 °C 104 °C 750 - 800 °C 160 cm3/min 60 min 3 Torr 248 nm 100 mJ 10 Hz

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RESULTS

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DISCUSSION

The YBCO film prepared at 800 C showed 77 K of Tc(--0) on the MgO substrate and 87 K on the STO as grown. Spiral growth is observed for the YBCO film on the MgO substrate by AFM, that is not on the STO substrate. Figure 1 shows the temperature dependence of electrical resistivity of the YBCO films prepared at a temperature of 750 C for 40 min. with and without KrF laser irradiation. The resistivity of the film prepared with KrF irradiation shows the metallic decrease and Tc becomes higher than the other one. Tc of the film without laser irradiation is 69 K and that with laser irradiation is 85 K. Many grain boundaries are observed in the film prepared without laser irradiation by SEM and AFM (Fig. 2 (a)). The grain boundaries are hardly observed in the film with laser irradiation (Fig. 2 (b)). The grain boundaries are diminished by the irradiation of laser. Therefore, the property of superconductivity is improved. 4.

CONCLUSION

YBCO films are prepared by laser MQCVD using Ba(hfa)2-tetraglyme. Smoother surface and higher Tc film is obtained with laser irradiation. ,~, O 1.0 LO ¢N n" "" 0.8 In" ~) ¢) 0.6 C

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Fig. 2 SEM micrographs of the film surfaces of (a) YBCO film prepared without laser irradiation. (b) with laser irradiation.

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Acknowledgments

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This work supported by NEDO. We acknowledge Dr. H. Meinema (TNO Industrial Research, The Netherlands) for supply of Ba(hfa)2 tetraglyme.

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Fig. 1 Temperature dependance of electrical resistivity of the YBCO filmes prepared with and without laser irradiation.

References

[1] K. Timmer et. al, Inorg. Chim. Acta, 190 (1991) 109. [2] C.I.M.A. Spee et. at, J. Phy. IV Sept. (1991 C2-295.