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NdBa2Cu3O7-δ superconducting thin films made by the PLD method
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PHYSICA ®
~
ELSEVIER
Physica C 282-287 (1997) 677--fJ78
NdBa2CU30,-6 Superconducting Thin Films Made by the PLD Method Seung-Hyun Moon and Byungdu Oh LG Corporate Institute of Technology, 16 Woomyeon-dong Seocho-gu, Seoul 137-140, Korea We have made NdBa2Cu307_o (NBCO) thin films on (100) SrTi03(STO) substrates by the pulsed laser deposition (PLD) method. We have found the optimum deposition conditions in the mixed gas of oxygen and argon as well as in pure oxygen. The NBCO thin films of Te 93 - 93.5 K were obtained, and they were grown epitaxially with c-axis preferred orientation. The critical current density of the NBCO thin films were 1 - 2 X 106 Alcm2 at 77 K.
=
It was reported that bulk Ndl+xBa2-xCu307-0 (NBCO) materials made by the oxygen-controlledmelt growth (OCMG) method in the reduced oxygen atmosphere in argon gas have superconducting transition temperature (Te) of - 96 K,[1-5] which is the highest among RBa2Cu307_o where R is the rare earth material such as Nd, Sm, Eu, Gd, etc. In addition, the NBCO single crystals have shown a large critical current density (Je) at high applied magnetic field[3]. Hence, it was expected that good superconducting thin films made of NBCO material would have high Te and large Je. Several groups have made NBCO thin films with Te ~ 90 K by using the laser ablation method [6-8], as well as sputtering [9-10]. In this work, we report the study of various deposition conditions in the reduced oxygen atmosphere, by using the mixed gas of oxygen and argon during deposition. NBCO thin films were deposited on (100) SrTi03(STO) substrates by using the PLD method with a KrF (248 nm) eximer laser. The energy density and repetition rate of the laser were fixed at 2-3 J/cm2 and 10 Hz respectively, and the distance between target and substrate (dt-s) was - 6.8 cm. The typical deposition rate was about 5-10 nmlmin. The reduced oxygen environment during deposition was made by mixing oxygen and argon. Resistance vs. temperature (R vs. T) curves of NBCO thin films deposited at some optimized conditions in the mixed gas as well as in pure oxygen are in Fig. 1. The inset shows the transition region. The transition temperatures (Te's) of both NBCO films were in the range of 93 - 93.5 K. The NBCO thin film made in the mixed gas was deposited at 0921-4534/97/$17.00 @ Elsevier Science B.Y. All rights reserved. PH S0921-4534(97)00492-9
substrate temperature T sub. ::: 760°C, and total chamber pressure PlOt. =400 mTorr (P02 ::: 20 mTorr and PAr 380 mTorr). The one made in pure oxygen was deposited at T sub. =770°C and p::: 800 mTorr. The resistivity was smaller for the film made in the mixed gas, and it was about 0.2 mQcm, comparing to the film made in the pure oxygen of 0.35 mQcm at 300K. Fig. 2(a) shows Te as a function of Tsub. for NBCO thin films deposited at two different processing gas conditions at the same total pressure PlOt of 800 mTorr, for pure oxygen and the mixed gas of - 3 % O2 in Ar. We note that the substrate
=
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2
12
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90
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92
94
96
98
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4
o~~--~~~~==~
o
50
100
150
200
250
Temperature (K)
Fig. 1. Resistance vs. temperature curves of NBCO thin films deposited at optimized conditions in the mixed gas and pure oxygen. The inset shows the transition region.
678
S.-H. Moon. B. OhlPhysica C 282-287 (1997) 677-678
temperature range to produce thin films ofTe (R =0) > 90 K is broader for the mixed gas case, Tsub. 720 - 790°C, compared with the case of pure oxygen growth, T sub. =760 - 780°C. Fig. 2(b) shows Te as a function of the oxygen amount in the mixed gas (P02lPtot.) for three different 800 or total pressures during deposition. At Ptot. 1000 mTorr, the NBCO thin films of Te > 90 K could be obtained in broad range of 02/Ar ratio including pure oxygen growth. At lower total pressure of Ptot. = 400 mTorr, we obtained good superconducting NBCO thin films in the reduced oxygen process, but we could not obtain good superconducting NBCO thin films for any substrate temperature range of 700 - 810°C with only pure
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(a)
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REFERENCES
0
80
70
0
oxygen. In pure argon, in-situ NBCO thin films deposited at various conditions never showed superconducting or metallic properties The x-ray diffraction patterns of the NBCO thin films in Fig. 1. indicate that they have grown epitaxially on the (100) STO substrate with c-axis 6 2 preferred orientation. The Je's are 1 - 2 x 10 Alcm for NBCO thin films made both in pure oxygen and in the mixed gas. We found the optimum conditions producing highly c-axis oriented NBCO superconducting thin films for the mixed gas of oxygen and argon. The results indicate that we can make very good NBCO superconducting thin films of Te > 90 K in broader pressure and temperature range by using the mixed gas (i.e. reduced oxygen gas), compared with the deposition process in pure oxygen.
0.4
0.6
P IP O
2
0.8
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I
1.0
toL
Fig. 2. (a) The transition temperatures of NBCO thin films deposited at various substrate temperatures for two different gases at Ptot. = 800 mTorr. (b) Te as a function of the oxygen amount in the mixed gas (PozIPtod for three different total chamber pressures.
[1] S. I. Yoo, M. Murakami, N. Sakai, T. Higuchi, and S. Tanaka, lpn. l. Appl. Phys. 33, LlOOO (1994). [2] S. I. Yoo, N. Sakai, ~. Takaichi, T. Higuchi, and M. Murakami, Appl. Phys. Lett. 65, 633 (1994). [3] T. Egi, J. G. Wen, K. Kuroda, H. Unoki, and N. Koshizuka, Appl. Phys. Lett. 67,2406 (1995). [4] M. J. Kramer, S.1. Yoo, R. W. MacCallum, W. B. Yelon, H. Xie, and P. Allenspach, Physica C219, 145 (1994). [5] H. Shaked, B. W. Veal, J. Faber,Jr., R. L. Hitterman, U. Balachandran, G. Tomlins, H. Shi, L. Morss, and A. P. Paulikas, Phy. Rev. B41, 4173 (1990). [6] S. H. Moon and B. Oh, IEEE. Trans. on. Appl. Supercon. to be published. [7] M. Badaye, F. Wang, Y. Kanke, K. Fukushima, and T. Morishita, Appl. Phys. Lett. 66, 2131 (1995). [8] B. David, S. Krey, R. Eckart, V. Doorman, G. Rabe, J. P. Krumme, and O. Dossel, Applied Superconuctivity Conference 1996, Abstract EDC-I0 (1996). [9] I. S. Kim, K. W. Lee, Y. K. Park, and J. C. Park, Appl. Phys. Lett. 68, 1859 (1996). [10] J. Geerk, Y. R. Li, H. Kittel, R. Smithey, G. Ulmer, and G. Linker, Applied Superconuctivity Conference 1996, Abstract MBC-5 (1996).
PHYSICA ®
~
ELSEVIER
Physica C 282-287 (1997) 677--fJ78
NdBa2CU30,-6 Superconducting Thin Films Made by the PLD Method Seung-Hyun Moon and Byungdu Oh LG Corporate Institute of Technology, 16 Woomyeon-dong Seocho-gu, Seoul 137-140, Korea We have made NdBa2Cu307_o (NBCO) thin films on (100) SrTi03(STO) substrates by the pulsed laser deposition (PLD) method. We have found the optimum deposition conditions in the mixed gas of oxygen and argon as well as in pure oxygen. The NBCO thin films of Te 93 - 93.5 K were obtained, and they were grown epitaxially with c-axis preferred orientation. The critical current density of the NBCO thin films were 1 - 2 X 106 Alcm2 at 77 K.
=
It was reported that bulk Ndl+xBa2-xCu307-0 (NBCO) materials made by the oxygen-controlledmelt growth (OCMG) method in the reduced oxygen atmosphere in argon gas have superconducting transition temperature (Te) of - 96 K,[1-5] which is the highest among RBa2Cu307_o where R is the rare earth material such as Nd, Sm, Eu, Gd, etc. In addition, the NBCO single crystals have shown a large critical current density (Je) at high applied magnetic field[3]. Hence, it was expected that good superconducting thin films made of NBCO material would have high Te and large Je. Several groups have made NBCO thin films with Te ~ 90 K by using the laser ablation method [6-8], as well as sputtering [9-10]. In this work, we report the study of various deposition conditions in the reduced oxygen atmosphere, by using the mixed gas of oxygen and argon during deposition. NBCO thin films were deposited on (100) SrTi03(STO) substrates by using the PLD method with a KrF (248 nm) eximer laser. The energy density and repetition rate of the laser were fixed at 2-3 J/cm2 and 10 Hz respectively, and the distance between target and substrate (dt-s) was - 6.8 cm. The typical deposition rate was about 5-10 nmlmin. The reduced oxygen environment during deposition was made by mixing oxygen and argon. Resistance vs. temperature (R vs. T) curves of NBCO thin films deposited at some optimized conditions in the mixed gas as well as in pure oxygen are in Fig. 1. The inset shows the transition region. The transition temperatures (Te's) of both NBCO films were in the range of 93 - 93.5 K. The NBCO thin film made in the mixed gas was deposited at 0921-4534/97/$17.00 @ Elsevier Science B.Y. All rights reserved. PH S0921-4534(97)00492-9
substrate temperature T sub. ::: 760°C, and total chamber pressure PlOt. =400 mTorr (P02 ::: 20 mTorr and PAr 380 mTorr). The one made in pure oxygen was deposited at T sub. =770°C and p::: 800 mTorr. The resistivity was smaller for the film made in the mixed gas, and it was about 0.2 mQcm, comparing to the film made in the pure oxygen of 0.35 mQcm at 300K. Fig. 2(a) shows Te as a function of Tsub. for NBCO thin films deposited at two different processing gas conditions at the same total pressure PlOt of 800 mTorr, for pure oxygen and the mixed gas of - 3 % O2 in Ar. We note that the substrate
=
16
rn a
4
..
2
12
-
C
90
CD
92
94
96
98
U
...c III
8
II)
'i CD
a::
4
o~~--~~~~==~
o
50
100
150
200
250
Temperature (K)
Fig. 1. Resistance vs. temperature curves of NBCO thin films deposited at optimized conditions in the mixed gas and pure oxygen. The inset shows the transition region.
678
S.-H. Moon. B. OhlPhysica C 282-287 (1997) 677-678
temperature range to produce thin films ofTe (R =0) > 90 K is broader for the mixed gas case, Tsub. 720 - 790°C, compared with the case of pure oxygen growth, T sub. =760 - 780°C. Fig. 2(b) shows Te as a function of the oxygen amount in the mixed gas (P02lPtot.) for three different 800 or total pressures during deposition. At Ptot. 1000 mTorr, the NBCO thin films of Te > 90 K could be obtained in broad range of 02/Ar ratio including pure oxygen growth. At lower total pressure of Ptot. = 400 mTorr, we obtained good superconducting NBCO thin films in the reduced oxygen process, but we could not obtain good superconducting NBCO thin films for any substrate temperature range of 700 - 810°C with only pure
=
=
(a)
100
95 90
I
Q' .... 85 ~u
I ;':I:!
II
0
6
6
6 ·0·:
75
pure 02
-e-:Ar+0
640
0
680
720
760
2
800
840
T.Ub (OC)
(b)
100 95
g ~u
90
If ~*
9
)(
X
9
6
f lie
6
85
=400 mTorr =800 mTorr tot. : P =1000 mTorr tot.
1-0- : P
tot.
.. ·0.... : P
80
.. ·x....
0.0
0.2
REFERENCES
0
80
70
0
oxygen. In pure argon, in-situ NBCO thin films deposited at various conditions never showed superconducting or metallic properties The x-ray diffraction patterns of the NBCO thin films in Fig. 1. indicate that they have grown epitaxially on the (100) STO substrate with c-axis 6 2 preferred orientation. The Je's are 1 - 2 x 10 Alcm for NBCO thin films made both in pure oxygen and in the mixed gas. We found the optimum conditions producing highly c-axis oriented NBCO superconducting thin films for the mixed gas of oxygen and argon. The results indicate that we can make very good NBCO superconducting thin films of Te > 90 K in broader pressure and temperature range by using the mixed gas (i.e. reduced oxygen gas), compared with the deposition process in pure oxygen.
0.4
0.6
P IP O
2
0.8
•olie
I
1.0
toL
Fig. 2. (a) The transition temperatures of NBCO thin films deposited at various substrate temperatures for two different gases at Ptot. = 800 mTorr. (b) Te as a function of the oxygen amount in the mixed gas (PozIPtod for three different total chamber pressures.
[1] S. I. Yoo, M. Murakami, N. Sakai, T. Higuchi, and S. Tanaka, lpn. l. Appl. Phys. 33, LlOOO (1994). [2] S. I. Yoo, N. Sakai, ~. Takaichi, T. Higuchi, and M. Murakami, Appl. Phys. Lett. 65, 633 (1994). [3] T. Egi, J. G. Wen, K. Kuroda, H. Unoki, and N. Koshizuka, Appl. Phys. Lett. 67,2406 (1995). [4] M. J. Kramer, S.1. Yoo, R. W. MacCallum, W. B. Yelon, H. Xie, and P. Allenspach, Physica C219, 145 (1994). [5] H. Shaked, B. W. Veal, J. Faber,Jr., R. L. Hitterman, U. Balachandran, G. Tomlins, H. Shi, L. Morss, and A. P. Paulikas, Phy. Rev. B41, 4173 (1990). [6] S. H. Moon and B. Oh, IEEE. Trans. on. Appl. Supercon. to be published. [7] M. Badaye, F. Wang, Y. Kanke, K. Fukushima, and T. Morishita, Appl. Phys. Lett. 66, 2131 (1995). [8] B. David, S. Krey, R. Eckart, V. Doorman, G. Rabe, J. P. Krumme, and O. Dossel, Applied Superconuctivity Conference 1996, Abstract EDC-I0 (1996). [9] I. S. Kim, K. W. Lee, Y. K. Park, and J. C. Park, Appl. Phys. Lett. 68, 1859 (1996). [10] J. Geerk, Y. R. Li, H. Kittel, R. Smithey, G. Ulmer, and G. Linker, Applied Superconuctivity Conference 1996, Abstract MBC-5 (1996).