- Email: [email protected]
PLD method
Physica C 412–414 (2004) 801–806 www.elsevier.com/locate/physc
Development of 100-m long Y-123 coated conductors processed by IBAD/PLD method Y. Iijima *, K. Kakimoto, Y. Sutoh, S. Ajimura, T. Saitoh Materials Research Laboratory, Fujikura Ltd., 1-5-1, Kiba, Koto-ku, Tokyo 135-8512, Japan Received 29 October 2003; accepted 15 December 2003 Available online 1 June 2004
Abstract 100-m class Y-123 coated conductors were demonstrated by using reel-to-reel vacuum apparatuses of ion-beamassisted-deposition (IBAD) and pulsed-laser-deposition (PLD). The window for Gd2 Zr2 O7 deposition condition was quite wide and 100-m long IBAD-Gd2 Zr2 O7 template films were routinely obtained with D/ of 10 on non-textured Ni-alloy tapes. 100-m long second buffer layers of Y2 O3 or CeO2 were grown by PLD on the IBAD templates with D/ of 7–8, or 5–6, respectively. Y-123 films with D/ of 7 were formed on the substrate of Y2 O3 //IBAD-Gd2 Zr2 O7 // Hastelloy by PLD. End-to-end Ic of 38 A and Jc of 0.76 MA/cm2 (77 K, self-field) were obtained in a 100-m long sample. On the other hand, D/ of 3 was obtained on the substrate of CeO2 //IBAD-Gd2 Zr2 O7 //Hastelloy. Jc of 2.9 MA/cm2 were obtained in a 0.1-m long Y-123 film, and Jc was improved to 1.6 MA/cm2 for an 80-m long Y-123 tape. 2004 Elsevier B.V. All rights reserved. PACS: 68.55.Jk; 74.76.Bz; 81.05.Je; 81.15.Jj Keywords: Y-123 coated conductors; Ion-beam-assisted deposition (IBAD); Pulsed-laser-deposition (PLD)
1. Introduction In recent years remarkable progress has been made on Y-123 coated conductor technology aiming excellent Jc properties as single crystal Y123 films even on long flexible substrate. The most essential factor for the technique is biaxial crystalline alignment control of HTS films on metallic tapes, in order to diminish weaklinks at misaligned
*
Corresponding author. Tel.: +81-3-5606-1064; fax: +81-35606-1512. E-mail address: [email protected] (Y. Iijima).
grain boundaries. Many methods were proposed and examined in the past decade [1]. Ion-beam-assisted deposition (IBAD) is characterized as direct deposition of textured templates of YSZ, Gd2 Zr2 O7 , etc. on non-textured substrates at quite low temperature [2]. Quite smooth and highly textured oxide template films are obtained without degradation coming from grain boundaries of metal substrates, because no epitaxial relationships required with metal tapes. Recent progress of vacuum technologies makes it possible to fabricate reliable long length substrates by IBAD [3]. Pyrochlore type oxide of Gd2 Zr2 O7 had an advantage of faster texture evolution than YSZ
0921-4534/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2003.12.075
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Y. Iijima et al. / Physica C 412–414 (2004) 801–806
[4]. It has rather higher growth temperature of 200 C, which also contribute to improve long length processing stability because large-diameter ion source itself has strong heat radiation and sometimes water-cooling was required to control substrate temperature for YSZ growth. Pulsed-laser-deposition (PLD) process has also greatly advanced for Y-123 films on long flexible tapes. It is characterized with very stable stoicheometry, optimal oxygen pressure, high growth rate, etc. Ic over 300 A was reported using the combination of IBAD and PLD process by Usoskin et al. [5]. Furthermore, quite effective second CeO2 buffer layer was found by Muroga et al. to improve in-plane texture by high-rate PLD process on IBAD-Gd2 Zr2 O7 [6]. The optimization of the PLD/IBAD-combined buffer layer should also contribute to improve processing speed of IBAD and PLD method. In order to reduce the manufacturing cost, faster processing speed is the most essential. In this paper we describe recent development of reel-to-reel IBAD and PLD process for 100-m length Y-123 tapes using the architecture of Y-123//Y2 O3 //IBADGd2 Zr2 O7 //Hastelloy and Y-123//CeO2 //IBADGd2 Zr2 O7 //Hastelloy.
2. Experimental 2.1. IBAD process Biaxially aligned Gd2 Zr2 O7 films were deposited by reel-to-reel, dual-ion-beam sputtering system equipped with two sets of RF discharged 66cm · 6-cm square-shaped ion sources, as shown in Fig. 1. Substrates used were roll-milled tapes of Hastelloy C276 with 10-mm width and 100 lm thick, the average roughness of which was below 30nm. The deposition area was uniformly heated up to 150–200 C. 1–2 lm thick Gd2 Zr2 O7 films were continuously grown on tape moving speed of 0.5–1.0 m/h. Arþ assisting ions with the energy of 200 eV bombarded films during growth with ion incident angle of 55. Characterization of the assisting ion beam was performed by using a beam divergence sensor that is composed of Faraday cups shifting behind slit apertures.
Fig. 1. Schematic diagram of reel-to-reel IBAD system to deposit biaxially textured template films on long metal tapes. A beam divergence sensor was applied to characterize the assisting ion beam.
2.2. PLD process Second buffer layers of Y2 O3 , or CeO2 films were grown by a reel-to-reel PLD on IBADGd2 Zr2 O7 template films, system using Kr-F (k ¼ 248nm) excimer laser. The temperature of substrate was 500–1000 C, where the oxygen pressure was below 20 mTorr. The deposition was repeated for several times at the tape-moving speed of 4.5 m/h. Y-123 films were produced by the reel-to-reel PLD system also using Kr-F excimer laser. The laser pulse energy was 200–300 mJ with the repetition rate of 200Hz, at the temperature of 700–750 C, where the oxygen pressure was 200 mTorr. Tape-moving speed was 1.0–4.0 m/h. Ag cap layer of 10 lm thickness was deposited by reel-to-reel magnetron sputtering. Thereafter heat-treatment was done for 2 h at 500 C in 760 Torr oxygen. Crystalline structures were measured by XRD and TEM observation. The in-plane alignment ðD/Þ was evaluated by a full width at half maximum (FWHM) value of /-scan for Gd2 Zr2 O7 (2 2 2), CeO2 (2 2 0), Y2 O3 (2 2 2), and Y-123 (1 0 3) pole. Transport properties were measured at 77 K,
in self-field by DC four-probe method. Voltage taps were attached at every 5-m length.
deg.
Y. Iijima et al. / Physica C 412–414 (2004) 801–806 40
Divergence, ∆φ
3.1. Processing stability for 100-m long IBAD template films
GZO∆ φ
Divergence
35 30
3. Results and discussion
803
Ar+:200eV
25 20 15 10 5 0
0
200
400
600
800
Beam current (mA) Fig. 3. Beam current dependence for the assisting beam divergence at the beam energy of 200 eV, and resulting in-plane texture of Gd2 Zr2 O7 template films.
threshold around 200 mA, which corresponded to about ion current density of 100 lA/cm2 at the substrate, to an upper threshold at 500 mA, which corresponded to the beam divergence of 20. The results indicate that process window of Gd2 Zr2 O7 film is wide for ion current density and beam divergence, which support high reproducibility of IBAD-Gd2 Zr2 O7 . During long time and continuous operation of ion sources, the condition of discharge plasma gradually changes. Fig. 4 shows the variation of beam divergent angle during long time operation. Though slight instability was observed just after the start, beam divergence are quite stable during long time operation. The results indicate the stability of ion beam condition is sufficient enough to get good uniformity of 100-m long template films [7].
40 beam diverenceg
35 30
GZO ∆ φ
Ar+ : 300mA
25 20 15 10 5 0
0
200
400
600
800
1000 1200
200eV Beam Voltage (V)
25
Divergence (deg.)
Divergence, ∆φ (deg.)
Biaxial alignment of IBAD templates sensitively depended on ion incident angle toward substrates [2], which suggests unidentified parameters like beam divergence can affect texture of growing films. The ion energy and total ion current are fixed by power source, but several other parameters such as ion current density, beam divergence, etc. are usually unidentified. Fig. 2 shows the beam energy dependence for the assisting beam divergence at the beam current of 300 mA, and resulting in-plane texture of Gd2 Zr2 O7 template films. Sharp beam energy dependence was observed for D/ of Gd2 Zr2 O7 films, which peaked at the optimized energy of 200 eV. On the other hand, the optimized beam energy for minimum divergence was 400–500eV. Fig. 3 shows the beam current dependence for the assisting beam divergence at the beam energy of 200 eV, and resulting in-plane texture of Gd2 Zr2 O7 template films. In this beam energy the beam divergence decreased with lowering the beam current. On the other hand the optimized processing window of beam current is quite wide from a lower
Ar+beam current : 500mA
20
Ar+beam current : 400mA
15 10
Ar+:200eV
5 0
0
20
10 cm transmitted beam from the ion source
40
60
80
Operation Time (hours) Fig. 2. Beam energy dependence for the assisting beam divergence at the beam current of 300 mA, and resulting in-plane texture of Gd2 Zr2 O7 template films.
Fig. 4. Stability of ion beam divergent angle during long time operation of RF linear type ion source.
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Y. Iijima et al. / Physica C 412–414 (2004) 801–806
3.2. Texture improvement of 100-m long buffer layers by PLD The IBAD-template materials as YSZ or Gd2 Zr2 O7 had a problem of slight chemical interactions with Y-123 film, which produces a thin, reacted layer of BaZrO3 . Thin Y2 O3 or CeO2 films were usually introduced between Y-123 and IBAD-template films [3–5], with the argument of chemical reaction or lattice mismatching [8]. Recently clear ‘‘self-alignment effect’’ was found in the second buffer layer of CeO2 [6], or Gd2 Zr2 O7 [9]. Fig. 5 shows the thickness dependence of D/ value for Y2 O3 (2 2 2), Gd2 Zr2 O7 (2 2 2), and CeO2 (2 2 0) poles. Surface in-plane texture for the second buffers of CeO2 or Gd2 Zr2 O7 improved rapidly without ion bombardment on textured IBAD-Gd2 Zr2 O7 template films. The conditions A, B, and C shown as in Fig. 5 were chosen for the textured substrate to deposit Y-123 films. Uniformly aligned 100-m long buffer layers of Y2 O3 //IBAD-Gd2 Zr2 O7 //Hastelloy and CeO2 // IBAD-Gd2 Zr2 O7 //Hastelloy were routinely obtained as shown in Table 1, with the conditions of A and B. D/ values for Y-123 (1 0 3) poles grown on the buffer layers were also indicated. Fig. 6
Fig. 6. XRD pole figures and /-scans of (a) IBAD-Gd2 Zr2 O7 (2 2 2), (b) CeO2 (2 2 0), and (c) Y-123 (1 0 3) for a tape formed as the structure of Y-123//CeO2 //IBAD-Gd2 Zr2 O7 //Hastelloy.
12
∆φ (°)
10 8
IBAD-GZO
A
Y 2 O3
C
6 4 CeO2
B
Gd 2 Zr 2O7
2 00
0.5
1
1.5
Thickness(µm) Fig. 5. Thickness dependence of in-plane texture ðD/Þ for second buffer layers of CeO2 , Gd2 Zr2 O7 , and Y2 O3 grown by PLD on IBAD-Gd2 Zr2 O7 template films with D/ of 10. The conditions A, B, and C were chosen for the textured substrate to deposit Y-123 films.
shows XRD pole figures and /-scans for an end point of 100-m long tape with the architecture of Y-123//CeO2 //Gd2 Zr2 O7 //Hastelloy. D/ value of 3 was obtained for long length Y-123 in the condition of A. Nearly equal sharp texture was observed in a Y-123 film using Gd2 Zr2 O7 second buffer with the condition C for a short sample. 3.3. 100-m long Y-123 tapes processed by PLD Table 2 summarizes Ic =Jc properties for 0.1 m long samples of Y-123//Y2 O3 //IBAD-Gd2 Zr2 O7 //
Table 1 In-plane texture for 100-m long buffer layers and Y-123 films grown on them Second buffer materials
D/ of IBAD-GZO
D/ of second buffer layer
D/ of Y-123
Y2 O3 CeO2
10–11
7–8 5–6
7–8 3–5
*
In-plane texture for surface of CeO2 should be better than D/ values measured by XRD.
Y. Iijima et al. / Physica C 412–414 (2004) 801–806
805
Table 2 Ic =Jc properties for 0.1-m long short samples Substrate
D/ (GdZrO)
D/ (Y-123)
Ic (A)
Jc (A/cm2 )
Thickness (lm)
Y2 O3 //IBAD-Gd2 Zr2 O7 //Hastelloy
11 11 11
7 7 7
77 150 123
1.9M 1.3M 0.8M
0.4 1.2 1.5
CeO2 //IBAD-Gd2 Zr2 O7 //Hastelloy
11 11 11
3 3 5
100 160 190
2.9M 1.4M 1.3M
0.4 1.2 1.5
Fig. 8. The photograph of the 100-m length Y-123 tape for Fig. 7.
1000
Y-123//CeO2//GZO//Hastelloy Ic=32A Jc=1.6MA/cm2 (40m)
100
Ic (A)
Hastelloy and Y-123//CeO2 //IBAD-Gd2 Zr2 O7 // Hastelloy structures. Jc value increased to 2.9 MA/ cm2 by using sharply textured CeO2 buffer layer, where Ic reached 190 A with a 1.5 lm thick Y-123 film. Fig. 7 shows longitudinal Ic distributions for an Y-123 film with D/ of 7 formed by PLD on 100-m length buffer layers of Y2 O3 //IBADGd2 Zr2 O7 //Hastelloy. Ic of 38 A and Jc of 0.76 MA/cm2 (77 K, self-field) were obtained in endto-end of 100 m length. A half of the sample, 55 m, could transport zero resistive current over 40 A. Ic L values reached 3800 A m. The photograph for the 100-m sample was shown in Fig. 8. Fig. 9 shows longitudinal Ic distributions for an 80-m long Y-123//CeO2 //IBAD-Gd2 Zr2 O7 // Hastelloy tape. Jc of 1.6 MA/cm2 was uniformly obtained except a gap observed near the middle of the tape. In this part no current could transport without resistivity. Short-length degradation
10 Handling mistake
1000
Y-123//Y2O3//GZO//Hastelloy I c (A)
1
I c =38A Jc =0.76MA/cm 2
100
55m Ic>40
0
20
40
40
60
80
100
Fig. 9. Longitudinal Ic distributions for a 80-m length Y-123 tape formed as Y-123//CeO2 //IBAD-Gd2 Zr2 O7 //Hastelloy.
77K, 0T 1
20
Position (m)
(100-m end-to-end)
10
0
77K, 0T
60
80
100
120
Position (m) Fig. 7. Longitudinal Ic distributions for a 100-m length Y-123 tape formed as Y-123//Y2 O3 //IBAD-Gd2 Zr2 O7 //Hastelloy.
coming from handling mistake was observed inside the part. Fig. 10 shows the improvement of Ic L values for Y-123 tapes formed by our IBAD/PLD process in the past decade, approaching the required performance of the practical Y123 conductors.
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Y. Iijima et al. / Physica C 412–414 (2004) 801–806
reaction at the interface of Y-123 and second buffer layers [7]. They mainly depend on precise control of substrate temperature and stability of evaporation mode at target surface during Y-123 film growth. It is essential to improve uniformity of deposition conditions at Y-123 growth surface during long time and continuous operation.
Acknowledgements Fig. 10. Development of Ic L values for Y-123 tapes formed by our IBAD/PLD process in the past decade.
4. Summary 100-m class Y-123 coated conductors were formed by IBAD and PLD. Process window for IBAD-Gd2 Zr2 O7 films were quite wide and long time operation of ion source was stable enough to keep the condition inside the window. Uniformly textured 100-m long template films for PLD-Y2 O3 // IBAD-Gd2 Zr2 O7 and PLD-CeO2 //IBADGd2 Zr2 O7 were routinely obtained on non-textured Ni-alloy tapes with D/ of 7–8 and 5–6, respectively. Ic of 38 A and Jc of 0.76 MA/cm2 (77 K, selffield) was obtained in end-to-end of a 100 m long Y-123//Y2 O3 //IBAD-Gd2 Zr2 O7 //Hastelloy tape. Jc was improved to 2.9 MA/cm2 for a short sample with D/ of 3, and to 1.6 MA/cm2 for a 80-m long Y-123 tape by using sharply textured second buffer layer of CeO2 . It was quite effective for Jc improvement up to the level of single crystal Y-123 films. The origins for Jc scattering for long samples other than handling mistakes could be considered as (a) insufficient crystallization including a-axis aligned grains for thick Y-123 films, (b) chemical
This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) as Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications.
References [1] Y. Iijima, K. Matsumoto, Supercond. Sci. Technol. 13 (1) (2000) 68. [2] Y. Iijima, K. Onabe, N. Futaki, N. Tanabe, N. Sadakata, O. Kohno, Y. Ikeno, IEEE Trans. Appl. Supercond. 3 (1993) 1510. [3] Y. Iijima, K. Kakimoto, M. Kimura, K. Takeda, T. Saitoh, IEEE Trans. Appl. Supercond. 12 (2001) 2816. [4] Y. Iijima, K. Kakimoto, T. Saitoh, T. Kato, T. Hirayama, Physica C 378–381 (2002) 960. [5] A. Usoskin, H.C. Freyhardt, A. Issaev, J. Dzick, J. Knoke, M.P. Oomen, M. Leghissa, H.W. Neumueller, IEEE Trans. Appl. Supercond. 13 (2003) 2452. [6] T. Muroga, T. Araki, T. Niwa, Y. Iijima, T. Saitoh, I. Hirabayashi, Y. Yamada, Y. Shiohara, IEEE Trans. Appl. Supercond. 13 (2003) 2532. [7] K. Kakimoto, Y. Iijima, T. Saitoh, Physica C 392–396 (2003) 783. [8] T.G. Holesinger, S.R. Foltyn, P.N. Arendt, Q.X. Jia, P.C. Dowden, R.F. DePaula, J.R. Groves, IEEE Trans. Appl. Supercond. 12 (2001) 3359. [9] Y. Sutoh, K. Kakimoto, Y. Iijima, T. Saitoh, Physica C submitted for publication.
Development of 100-m long Y-123 coated conductors processed by IBAD/PLD method Y. Iijima *, K. Kakimoto, Y. Sutoh, S. Ajimura, T. Saitoh Materials Research Laboratory, Fujikura Ltd., 1-5-1, Kiba, Koto-ku, Tokyo 135-8512, Japan Received 29 October 2003; accepted 15 December 2003 Available online 1 June 2004
Abstract 100-m class Y-123 coated conductors were demonstrated by using reel-to-reel vacuum apparatuses of ion-beamassisted-deposition (IBAD) and pulsed-laser-deposition (PLD). The window for Gd2 Zr2 O7 deposition condition was quite wide and 100-m long IBAD-Gd2 Zr2 O7 template films were routinely obtained with D/ of 10 on non-textured Ni-alloy tapes. 100-m long second buffer layers of Y2 O3 or CeO2 were grown by PLD on the IBAD templates with D/ of 7–8, or 5–6, respectively. Y-123 films with D/ of 7 were formed on the substrate of Y2 O3 //IBAD-Gd2 Zr2 O7 // Hastelloy by PLD. End-to-end Ic of 38 A and Jc of 0.76 MA/cm2 (77 K, self-field) were obtained in a 100-m long sample. On the other hand, D/ of 3 was obtained on the substrate of CeO2 //IBAD-Gd2 Zr2 O7 //Hastelloy. Jc of 2.9 MA/cm2 were obtained in a 0.1-m long Y-123 film, and Jc was improved to 1.6 MA/cm2 for an 80-m long Y-123 tape. 2004 Elsevier B.V. All rights reserved. PACS: 68.55.Jk; 74.76.Bz; 81.05.Je; 81.15.Jj Keywords: Y-123 coated conductors; Ion-beam-assisted deposition (IBAD); Pulsed-laser-deposition (PLD)
1. Introduction In recent years remarkable progress has been made on Y-123 coated conductor technology aiming excellent Jc properties as single crystal Y123 films even on long flexible substrate. The most essential factor for the technique is biaxial crystalline alignment control of HTS films on metallic tapes, in order to diminish weaklinks at misaligned
*
Corresponding author. Tel.: +81-3-5606-1064; fax: +81-35606-1512. E-mail address: [email protected] (Y. Iijima).
grain boundaries. Many methods were proposed and examined in the past decade [1]. Ion-beam-assisted deposition (IBAD) is characterized as direct deposition of textured templates of YSZ, Gd2 Zr2 O7 , etc. on non-textured substrates at quite low temperature [2]. Quite smooth and highly textured oxide template films are obtained without degradation coming from grain boundaries of metal substrates, because no epitaxial relationships required with metal tapes. Recent progress of vacuum technologies makes it possible to fabricate reliable long length substrates by IBAD [3]. Pyrochlore type oxide of Gd2 Zr2 O7 had an advantage of faster texture evolution than YSZ
0921-4534/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2003.12.075
802
Y. Iijima et al. / Physica C 412–414 (2004) 801–806
[4]. It has rather higher growth temperature of 200 C, which also contribute to improve long length processing stability because large-diameter ion source itself has strong heat radiation and sometimes water-cooling was required to control substrate temperature for YSZ growth. Pulsed-laser-deposition (PLD) process has also greatly advanced for Y-123 films on long flexible tapes. It is characterized with very stable stoicheometry, optimal oxygen pressure, high growth rate, etc. Ic over 300 A was reported using the combination of IBAD and PLD process by Usoskin et al. [5]. Furthermore, quite effective second CeO2 buffer layer was found by Muroga et al. to improve in-plane texture by high-rate PLD process on IBAD-Gd2 Zr2 O7 [6]. The optimization of the PLD/IBAD-combined buffer layer should also contribute to improve processing speed of IBAD and PLD method. In order to reduce the manufacturing cost, faster processing speed is the most essential. In this paper we describe recent development of reel-to-reel IBAD and PLD process for 100-m length Y-123 tapes using the architecture of Y-123//Y2 O3 //IBADGd2 Zr2 O7 //Hastelloy and Y-123//CeO2 //IBADGd2 Zr2 O7 //Hastelloy.
2. Experimental 2.1. IBAD process Biaxially aligned Gd2 Zr2 O7 films were deposited by reel-to-reel, dual-ion-beam sputtering system equipped with two sets of RF discharged 66cm · 6-cm square-shaped ion sources, as shown in Fig. 1. Substrates used were roll-milled tapes of Hastelloy C276 with 10-mm width and 100 lm thick, the average roughness of which was below 30nm. The deposition area was uniformly heated up to 150–200 C. 1–2 lm thick Gd2 Zr2 O7 films were continuously grown on tape moving speed of 0.5–1.0 m/h. Arþ assisting ions with the energy of 200 eV bombarded films during growth with ion incident angle of 55. Characterization of the assisting ion beam was performed by using a beam divergence sensor that is composed of Faraday cups shifting behind slit apertures.
Fig. 1. Schematic diagram of reel-to-reel IBAD system to deposit biaxially textured template films on long metal tapes. A beam divergence sensor was applied to characterize the assisting ion beam.
2.2. PLD process Second buffer layers of Y2 O3 , or CeO2 films were grown by a reel-to-reel PLD on IBADGd2 Zr2 O7 template films, system using Kr-F (k ¼ 248nm) excimer laser. The temperature of substrate was 500–1000 C, where the oxygen pressure was below 20 mTorr. The deposition was repeated for several times at the tape-moving speed of 4.5 m/h. Y-123 films were produced by the reel-to-reel PLD system also using Kr-F excimer laser. The laser pulse energy was 200–300 mJ with the repetition rate of 200Hz, at the temperature of 700–750 C, where the oxygen pressure was 200 mTorr. Tape-moving speed was 1.0–4.0 m/h. Ag cap layer of 10 lm thickness was deposited by reel-to-reel magnetron sputtering. Thereafter heat-treatment was done for 2 h at 500 C in 760 Torr oxygen. Crystalline structures were measured by XRD and TEM observation. The in-plane alignment ðD/Þ was evaluated by a full width at half maximum (FWHM) value of /-scan for Gd2 Zr2 O7 (2 2 2), CeO2 (2 2 0), Y2 O3 (2 2 2), and Y-123 (1 0 3) pole. Transport properties were measured at 77 K,
in self-field by DC four-probe method. Voltage taps were attached at every 5-m length.
deg.
Y. Iijima et al. / Physica C 412–414 (2004) 801–806 40
Divergence, ∆φ
3.1. Processing stability for 100-m long IBAD template films
GZO∆ φ
Divergence
35 30
3. Results and discussion
803
Ar+:200eV
25 20 15 10 5 0
0
200
400
600
800
Beam current (mA) Fig. 3. Beam current dependence for the assisting beam divergence at the beam energy of 200 eV, and resulting in-plane texture of Gd2 Zr2 O7 template films.
threshold around 200 mA, which corresponded to about ion current density of 100 lA/cm2 at the substrate, to an upper threshold at 500 mA, which corresponded to the beam divergence of 20. The results indicate that process window of Gd2 Zr2 O7 film is wide for ion current density and beam divergence, which support high reproducibility of IBAD-Gd2 Zr2 O7 . During long time and continuous operation of ion sources, the condition of discharge plasma gradually changes. Fig. 4 shows the variation of beam divergent angle during long time operation. Though slight instability was observed just after the start, beam divergence are quite stable during long time operation. The results indicate the stability of ion beam condition is sufficient enough to get good uniformity of 100-m long template films [7].
40 beam diverenceg
35 30
GZO ∆ φ
Ar+ : 300mA
25 20 15 10 5 0
0
200
400
600
800
1000 1200
200eV Beam Voltage (V)
25
Divergence (deg.)
Divergence, ∆φ (deg.)
Biaxial alignment of IBAD templates sensitively depended on ion incident angle toward substrates [2], which suggests unidentified parameters like beam divergence can affect texture of growing films. The ion energy and total ion current are fixed by power source, but several other parameters such as ion current density, beam divergence, etc. are usually unidentified. Fig. 2 shows the beam energy dependence for the assisting beam divergence at the beam current of 300 mA, and resulting in-plane texture of Gd2 Zr2 O7 template films. Sharp beam energy dependence was observed for D/ of Gd2 Zr2 O7 films, which peaked at the optimized energy of 200 eV. On the other hand, the optimized beam energy for minimum divergence was 400–500eV. Fig. 3 shows the beam current dependence for the assisting beam divergence at the beam energy of 200 eV, and resulting in-plane texture of Gd2 Zr2 O7 template films. In this beam energy the beam divergence decreased with lowering the beam current. On the other hand the optimized processing window of beam current is quite wide from a lower
Ar+beam current : 500mA
20
Ar+beam current : 400mA
15 10
Ar+:200eV
5 0
0
20
10 cm transmitted beam from the ion source
40
60
80
Operation Time (hours) Fig. 2. Beam energy dependence for the assisting beam divergence at the beam current of 300 mA, and resulting in-plane texture of Gd2 Zr2 O7 template films.
Fig. 4. Stability of ion beam divergent angle during long time operation of RF linear type ion source.
804
Y. Iijima et al. / Physica C 412–414 (2004) 801–806
3.2. Texture improvement of 100-m long buffer layers by PLD The IBAD-template materials as YSZ or Gd2 Zr2 O7 had a problem of slight chemical interactions with Y-123 film, which produces a thin, reacted layer of BaZrO3 . Thin Y2 O3 or CeO2 films were usually introduced between Y-123 and IBAD-template films [3–5], with the argument of chemical reaction or lattice mismatching [8]. Recently clear ‘‘self-alignment effect’’ was found in the second buffer layer of CeO2 [6], or Gd2 Zr2 O7 [9]. Fig. 5 shows the thickness dependence of D/ value for Y2 O3 (2 2 2), Gd2 Zr2 O7 (2 2 2), and CeO2 (2 2 0) poles. Surface in-plane texture for the second buffers of CeO2 or Gd2 Zr2 O7 improved rapidly without ion bombardment on textured IBAD-Gd2 Zr2 O7 template films. The conditions A, B, and C shown as in Fig. 5 were chosen for the textured substrate to deposit Y-123 films. Uniformly aligned 100-m long buffer layers of Y2 O3 //IBAD-Gd2 Zr2 O7 //Hastelloy and CeO2 // IBAD-Gd2 Zr2 O7 //Hastelloy were routinely obtained as shown in Table 1, with the conditions of A and B. D/ values for Y-123 (1 0 3) poles grown on the buffer layers were also indicated. Fig. 6
Fig. 6. XRD pole figures and /-scans of (a) IBAD-Gd2 Zr2 O7 (2 2 2), (b) CeO2 (2 2 0), and (c) Y-123 (1 0 3) for a tape formed as the structure of Y-123//CeO2 //IBAD-Gd2 Zr2 O7 //Hastelloy.
12
∆φ (°)
10 8
IBAD-GZO
A
Y 2 O3
C
6 4 CeO2
B
Gd 2 Zr 2O7
2 00
0.5
1
1.5
Thickness(µm) Fig. 5. Thickness dependence of in-plane texture ðD/Þ for second buffer layers of CeO2 , Gd2 Zr2 O7 , and Y2 O3 grown by PLD on IBAD-Gd2 Zr2 O7 template films with D/ of 10. The conditions A, B, and C were chosen for the textured substrate to deposit Y-123 films.
shows XRD pole figures and /-scans for an end point of 100-m long tape with the architecture of Y-123//CeO2 //Gd2 Zr2 O7 //Hastelloy. D/ value of 3 was obtained for long length Y-123 in the condition of A. Nearly equal sharp texture was observed in a Y-123 film using Gd2 Zr2 O7 second buffer with the condition C for a short sample. 3.3. 100-m long Y-123 tapes processed by PLD Table 2 summarizes Ic =Jc properties for 0.1 m long samples of Y-123//Y2 O3 //IBAD-Gd2 Zr2 O7 //
Table 1 In-plane texture for 100-m long buffer layers and Y-123 films grown on them Second buffer materials
D/ of IBAD-GZO
D/ of second buffer layer
D/ of Y-123
Y2 O3 CeO2
10–11
7–8 5–6
7–8 3–5
*
In-plane texture for surface of CeO2 should be better than D/ values measured by XRD.
Y. Iijima et al. / Physica C 412–414 (2004) 801–806
805
Table 2 Ic =Jc properties for 0.1-m long short samples Substrate
D/ (GdZrO)
D/ (Y-123)
Ic (A)
Jc (A/cm2 )
Thickness (lm)
Y2 O3 //IBAD-Gd2 Zr2 O7 //Hastelloy
11 11 11
7 7 7
77 150 123
1.9M 1.3M 0.8M
0.4 1.2 1.5
CeO2 //IBAD-Gd2 Zr2 O7 //Hastelloy
11 11 11
3 3 5
100 160 190
2.9M 1.4M 1.3M
0.4 1.2 1.5
Fig. 8. The photograph of the 100-m length Y-123 tape for Fig. 7.
1000
Y-123//CeO2//GZO//Hastelloy Ic=32A Jc=1.6MA/cm2 (40m)
100
Ic (A)
Hastelloy and Y-123//CeO2 //IBAD-Gd2 Zr2 O7 // Hastelloy structures. Jc value increased to 2.9 MA/ cm2 by using sharply textured CeO2 buffer layer, where Ic reached 190 A with a 1.5 lm thick Y-123 film. Fig. 7 shows longitudinal Ic distributions for an Y-123 film with D/ of 7 formed by PLD on 100-m length buffer layers of Y2 O3 //IBADGd2 Zr2 O7 //Hastelloy. Ic of 38 A and Jc of 0.76 MA/cm2 (77 K, self-field) were obtained in endto-end of 100 m length. A half of the sample, 55 m, could transport zero resistive current over 40 A. Ic L values reached 3800 A m. The photograph for the 100-m sample was shown in Fig. 8. Fig. 9 shows longitudinal Ic distributions for an 80-m long Y-123//CeO2 //IBAD-Gd2 Zr2 O7 // Hastelloy tape. Jc of 1.6 MA/cm2 was uniformly obtained except a gap observed near the middle of the tape. In this part no current could transport without resistivity. Short-length degradation
10 Handling mistake
1000
Y-123//Y2O3//GZO//Hastelloy I c (A)
1
I c =38A Jc =0.76MA/cm 2
100
55m Ic>40
0
20
40
40
60
80
100
Fig. 9. Longitudinal Ic distributions for a 80-m length Y-123 tape formed as Y-123//CeO2 //IBAD-Gd2 Zr2 O7 //Hastelloy.
77K, 0T 1
20
Position (m)
(100-m end-to-end)
10
0
77K, 0T
60
80
100
120
Position (m) Fig. 7. Longitudinal Ic distributions for a 100-m length Y-123 tape formed as Y-123//Y2 O3 //IBAD-Gd2 Zr2 O7 //Hastelloy.
coming from handling mistake was observed inside the part. Fig. 10 shows the improvement of Ic L values for Y-123 tapes formed by our IBAD/PLD process in the past decade, approaching the required performance of the practical Y123 conductors.
806
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reaction at the interface of Y-123 and second buffer layers [7]. They mainly depend on precise control of substrate temperature and stability of evaporation mode at target surface during Y-123 film growth. It is essential to improve uniformity of deposition conditions at Y-123 growth surface during long time and continuous operation.
Acknowledgements Fig. 10. Development of Ic L values for Y-123 tapes formed by our IBAD/PLD process in the past decade.
4. Summary 100-m class Y-123 coated conductors were formed by IBAD and PLD. Process window for IBAD-Gd2 Zr2 O7 films were quite wide and long time operation of ion source was stable enough to keep the condition inside the window. Uniformly textured 100-m long template films for PLD-Y2 O3 // IBAD-Gd2 Zr2 O7 and PLD-CeO2 //IBADGd2 Zr2 O7 were routinely obtained on non-textured Ni-alloy tapes with D/ of 7–8 and 5–6, respectively. Ic of 38 A and Jc of 0.76 MA/cm2 (77 K, selffield) was obtained in end-to-end of a 100 m long Y-123//Y2 O3 //IBAD-Gd2 Zr2 O7 //Hastelloy tape. Jc was improved to 2.9 MA/cm2 for a short sample with D/ of 3, and to 1.6 MA/cm2 for a 80-m long Y-123 tape by using sharply textured second buffer layer of CeO2 . It was quite effective for Jc improvement up to the level of single crystal Y-123 films. The origins for Jc scattering for long samples other than handling mistakes could be considered as (a) insufficient crystallization including a-axis aligned grains for thick Y-123 films, (b) chemical
This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) as Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications.
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