Physiea C 162-164 (1989) 1535-1536 North-Holland

Y1Ba=CusO~-a THIN FILMS ~ BY RF MAGNE/RON SPUTTERING

Satoshi TAKANO, Noriki HAYASHI, Shigeru OKUDA, Hajima HITOTSUYANAGI

Osaka Research Laboratories, Sumitomo Electric Ind., Ltd. 1-3, Shimaya 1-Chorea, Konohena-Ku, Osaka, 554 Japan

YtBa=Cu3Ov-s thin f i Ires were grown on (100)M¢0 and polycrystalline YSZ substrates by RF minetron eputteri~. We measured the magnetic f ield dependence of Jc of these films. ]he films gro~ on M¢O with Jc of 4.0xlO a, 2.9 xlO e and 1.5xlO" A/cm = at OT showed 7.1xl(P A/cm = at 8T, lx10" A/cm = at 20T and 1.1x10 = A/ca = at 5 T, respec- tively. We could obtain a c-axis oriented film with a Jc of 1.2xlO'A/cm = on YSZ polvcrystalline substrate, how- ever, it showed greater degradation than the f i Ims grown on ~ in Jc with maimetic field.

1. INTRODUCTION There have been many processes proposed for

manufacturing high-Tc oxide superconducting wires. Thin f i lm deposition is one of the most promising beause of i ts capabil i ty to produce highly aligned materials and because of the f l e x i b i l i t y of the films deposited on f lex ib le thin substrates.

For wire application, i t is important to obtain superconductors whose Jc is scarecely dependent on the magnetic f ie ld. Moreover i t is necessary to grow thin films on polycrys- ta l l ine substrates.

At the beginning of the research adapting thin fi lm deposition to wires, we tr ied to relate the magnetic f ie ld dependence on Jc to the structural features of Y1Ba=CusOv-a thin films grown on (100) MgO. Y1Ba=CusOv-s thin films were also deposited on polycrystal l ine f lex ib le YSZ. The magnetic f ie ld dependence of Jc and the structural features were also char- acterized in the case of the YSZ substrates.

2 Experimental The films were deposited on the substrates

heated to 700 ~ from a composite oxide target using conventuional RF magnetron sputtering. Sputtering was carried out in an Ar+IOXO= at- mosphere with pressures of 3xlO'=-8xlO -= torr . The fi lm thicknesses were 0.7-1.4 ~ and the growth rates were 0.2-0.4 A/s.

The films grown on NgO were annealed in 02 at 920~C for 2 hr and at 400 "C for 3 hr sub-

sequently. In the case of the films grown on polycrystal l ine YSZ, Tc(R=O) was decreased by annealing the films for the same time as the films grown on (100) MgO. Therefore, anneal- ing at 950"(3 for 10 min was selected for the films grown on polycrystall ine YSZ.

For al l films, Jc was measured at OT and 77.3 K by four-probe method under the cr i te -

rion of 1 ~V. Inductively coupled plasma absorption analysis (ICP) was used for the de- termination of composition. X-ray di f f ract ion (XRD), SEN and RHEED were ut i l ized for the characterization of structural features of the films.

RESULTS AND DISCUSSIONS We obtained films with Jc of 4.0x10 e,

2.3x10 e and 1.8x!04 A/cm = using MgO (100) sub- strates. Tc(R=O) of these films was 80-84 K. The magnetic f ie ld dependence on Jc was summa- rized in Fig. l . The effect of a magnetic f ie ld on Jc largely depended on the value of Jc at 0 T. The fi lm with Jc of 4.0x10 e A/cm = had an excellent Jc under an applied magnetic f ie ld and showed 7.1xlO" A/cm = even at 8 T. The fi lm with Jc of 2.3x10 e A/cm = showed larger degradatio in Jc with the magnetic f ie ld but had Jc of lx104 A/cm = even at 20 T. Though the largest degradation was observed with the f i lm with Jc of 1.8x104 A/cm =, 1/10 of the value of Jc at OT remained even at 5 T.

All of the films had a stoichiomotric com- position within the accuracy of ICP and no

0921--4534/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland)

1536 S. Takano et aL / YtBa2Cuj07_n thin films

~r _.-----! 4.ox,o,A~,~ ) ~ApT)' /I- '. i ×~0~,~; I

10 4 ~ / t .... (ATST)

~1 s ' I 1.3Xl(PAlr.n~ J " ~ ,-O (NOT)

• , [ i :

10= [ (AT OT)

10'10' f I [ ~ H

10 a [._4, i . . . . . . . . I i , - ~ 0 10 0 ~ '

H(T)

Fig. 1 Magnet ic f iel d dependence of the cr i t i ca l current densities of the films grown on (100)M¢0

~._ i~S~mm'~ , ~ T OT)

~' 10=- "--~ I (AT1T)

<

10'

tO ° I I I 10 "= 10" 10 ° MAGNETIC FIELD(T)

Fig.2 Magnetic f ie ld dependence of the cr i t i ca l current densities of the films grown on polycrystall ine YSZ substrates

peaks other than (001) were observed by XRD. The fi lm having Jc of 4.0x10 e A/cm = had a

smooth surface and dense, almost single crystal structures having s l ight irregular streaks by RHEED patterns. The f i lm having Jc of 1.8x104 A/cm = had polycrystall ine structures showing ring patterns with some spotty d i f f ract ion by RHEED.

We could obtain a f i lm with Jc of 1.2x104 A/ca = and Tc ( R=O ) of 90.3 K as the highest value using polycrystal l ine f lex ib le YSZ. It had smoother surface than the films having Jc of 1.8x10" A/cm = and I0 B A/cm = grown on (100) MgO. Moreover i t had the same high c-axis or i -

L

Fig.3 RHEED patterns of the films grown on (A) (lO0)MgO and on (B) polycrystall ine YSZ substrates

entation as seen in the films grown on (100) MgO. Dense structures without any voids were observed by cross-sectional SEM micrographs. Moreover another fi lm grown the YSZ substrate could be bent with a compressive strain up to 0.3 X without degradation in Jc.

Magnetic f ie ld dependence of Jc of the f i lm grown on YSZ was inferior to that of the fi lm with Jc of 1.8x104 A/cm 2 grown on (100) MgO as shown in Fig,2. RHEED patterns of the film grown on YSZ showed a typical polycrystall ine structure showing ring patterns without spotty d i f f ract ion as shown in Fig.3.

4. CONCLUSIONS Experimental results revealed the rela-

tionship between msgnetic f ie ld dependence on Jc and the structural features of the films. I t seems that the rotation of deposited grains in the a-b plane related to the magnetic f ie ld dependence on Jc. To improve the properties of the films grown on polycrystall ine YSZ, i t may be necessary to align the orientation in the a-b plane.

Though it may not be easy to control the alignment in the a-b plane, thin fi lm deposi- t ion has been proven to be useful for manufac- turing f lex ib le oxide superconductors.

REFERENCES 1. M.K.Wu,J.R.Ashburn,C.W.Chu,Phys.Rev.Lett.58,

908(1987) 2 T.Nakahara,Proceedings of the 1st Interna-

tional Symposium on Superconductivity,Nagoya, (1988) H.Hitotsuvanagi,K.Satou,T.Takano,M.Nagata, Proceedings of 39th Electronic Component Con- ference,Houston, 1989