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Superconducting thin films of Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O with Tc above 100 K
352
Journal of Crystal Growth 91(1988) 352—354 North-Holland, Amsterdam
SUPERCONDUCTING THIN FILMS OF Bi-Sr-Ca-Cu-O AND TI-Ba-Ca-Cu-O WITH 1~ABOVE 100 K Hideaki ADACHI, Kiyotaka WASA, Yo ICHIKAWA, Kumiko HIROCHI and Kentaro SETSUNE Central Research Laboratories, Matsushita Electric Industrial Co., Ltd., Moriguchi, Osaka 570, Japan Received 14 April 1988; manuscript received in final form 16 May 1988
Thin films of the Bi—Sr—Ca—Cu—O and Tl—Ba—Ca—Cu—O systems have been prepared on MgO substrates by RF-magnetron sputtering and subsequent annealing. These thin films showed a highly oriented structure with c axis perpendicular to the substrates. The Bi—Sr—Ca—Cu—O thin films exhibited superconducting transitions with the zero resistance temperature T~= 102 K and the 5 T1—Ba---Ca—Cu--O thin films hadsame 7~= order 100 K.ofThe critical as current density of thesystem. Bi—Sr—Ca—Cu—O thin films was as high as 2 X10 A/cm2 at 77 K, which was the magnitude the Ln—Ba—Cu—o
Thin films of the new high-7~oxide superconductors, Bi—Sr—Ca—Cu—O [1] and Ti—Ba—Ca— Cu—O [2], have recently received much attention, since the zero resistance temperature, 7~,is expected to be higher than 100 K. Attempts have been made to deposit thin films in the Bi—Sr—Ca—Cu—0 system by the sputtering. These experiments suggest that c-axis oriented thin films with 7~ 80 K can be successfully deposited on a crystalline substrate [3—5].The crystal structure corresponds to that of ceramics of the low 1~phase with the lattice constant c 30.6 A [6]. Occasionally, thin films with T~as high as 100 K were prepared using sputtering [7]. However, their crystal structure and superconducting properties are not well understood. In this paper we will describe the structural studies and superconducting properties of thin films of the Bi—Sr—Ca—Cu—0 and the Ti—Ba—Ca—Cu—O systern prepared by sputtenng deposition. Thin films of Bi compound and Tl compound were prepared by using an RF-planar magnetron sputtering system. Their targets were complex oxides of Bi—Sr—Ca—Cu and Ti—Ba—Ca—Cu, respectively. Typical sputtering conditions are shown in table 1. The Bi—Sr—Ca—Cu—O target was made by sintenng a mixture of Bi203 (99.999%), SrCO3 (99.9%), CaCO3 (99%) and CuO (99.9%) at 880°C =
for 8 h in air. The Ti—Ba—Ca—Cu—O target was made by sintering a mixture of Tl 203 (99.5%), BaCO3 (99.9%), CaCO3 (99%) and CuO (99.9%) at 910°Cfor 8 h in air. The as-sputtered films were postannealed at 850—900°C in 02 to improve their superconducting properties. Resistivity measurements were done using the standard DC four-probe method with gold electrodes deposited on the film surface. The critical current density was evaluated from the current— voltage characteristics. Thin films of the Bi compound were prepared at two substrate temperatures of 200 and 800°C. The sputtering targets were modulated to keep the film composition at 1—1—1—2 ratio of Bi—Sr—Ca— Cu within 10% accuracy. The annealing condition Table 1 Sputtering conditions Target
Complex oxide, 100~ Bi/Sr/Ca/Cu = 1.2—1.6/1/1—1.5/2 Tl/Ba/Ca/Cu = 2/1/2/3 Substrate (100) plane of MgO Substrate temperature 200 and 8000 C Sputtering gas Ar/02 = 1—1.5 Gas pressure 0.5 Pa RF input power 100—150 W Growth rate
0022-0248/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
50-80 A/mm
H. Adachi et al.
/
Superconducting thin films of Bi—Sr—Ca—Cu—O and Tl—Ba—Ca—Cu—O
(a)
—
spond to the high 7~phase of Bi—Sr—Ca—Cu—O with c = 36 A generally believed in the ceramics. These sputtered films showed the zero resistance ~H
0 ° C
H I
___ ..
I
j~l~_
_________________________________ 10
20
30 20
40 (deg I
50
60
10 ~.,
(b)
8
353
26
0
________________________________
to the ceramics temperature 7~= value 102 Kof(fig. 1052b), K which [1]. The wascrystal close structure of the sputtered Bi—Sr—Ca—Cu—O films with 7~= 102 K is not well understood. It is likely that the films are composed of a mixture of the high T~phase and the low 27~ phase. The high T~, phase may be segregated between the crystailites of the sputtered films of the low 7~phase and form current channels. Similar to the Bi—Sr—Ca—Cu—O system, thin films of Tl—Ba—Ca—Cu—O system were prepared by RF-magnetron sputtering. However, their chemical composition was quite unstable during the deposition and the postannealing process due to the high vapor pressure of Ti. Thin films were deposited without intentional heating of substrates (200°C) and annealed at 900°C for 30 mm in Tl
0 0
100 200 Temperature (K)
300
vapor. These annealed films showed a broad su-
Fig. 1. X-ray diffraction pattern and superconductivity of the Bi—Sr—Ca—Cu—O thin film deposited at 200°C and postannealed. The thickness is about 0.5 ~m.
was 890°C for 20 mm and subsequently 850—880°Cfor 5 h in oxygen atmosphere. Fig. 1 shows a typical X-ray diffraction pattern and re sistivity—temperature characteristic of a Bi—Sr— Ca—Cu—O thin film deposited at 200°C and postannealed. It is seen that the film has a highly oriented structure with c axis perpendicular to the substrate (fig. la). The lattice constant c is evaluated to be 30.64 A, which corresponds to the low 1~phase of Bi—Sr—Ca—Cu—O compound described for ceramics [6]. These thin films show the zero resistance temperature 7~= 70 K (fig. ib). The superconducting properties of the Bi—Sr— Ca—Cu—O thin films were strongly influenced by the substrate temperature in the deposition. Fig. 2 shows typical X-ray diffraction pattern and resistivity—temperature characteristics for the films deposited at 800°Cand postannealed. It is seen that the additional peaks are superposed on the periodical patterns of the low 7~phase at 20 = 24° and 34° (fig. 2a). The additional peaks may corre-
(a)
—
° C
~
~~
~
i~j~~
-__________________________________ 10
30
20
20
40
(degl
50
60
(b) o
a
~
2
.
1
0
0
0
200 300 (K) Fig. 2. X-ray diffraction pattern and superconductivity of the Bi—Sr—Ca—Cu—O thin film deposited at 800°C and postannealed. The thickness is about 0.2 ~sm. ‘
100
Temperature
354
H. Adachi et a!.
/ Superconducting thin films of Bi—Sr—Ca—Cu—O and
TI—Ba— Ca—Cu—O
2C
15 0
10 C
0~.
a
-
cc 0
100 Temperature
200
10
300
Fig. 3. Temperature dependence of the resistivity Tl—Ba—Ca—Cu—O thin film with 0.6 (im thickness.
20
30 20
(K)
for
perconducting transition at around 110 K and exhibited a zero resistance temperature I~= 100 K as shown in fig. 3. Fig. 4 shows the X-ray diffraction pattern of the Tl—Ba—Ca—Cu—O thin film, The periodical sharp peaks observed in the pattern indicate that the films are composed mainly of oriented structure. The main peaks can be assigned by the diffraction of material with lattice constant c = 36 A, as shown in the figure. This lattice constant c is close to the value reported in Tl—Ba—Ca—Cu—O ceramics [8]. The critical current density measured for the Bi—Sr—Ca—Cu—O films was as high as 2 X iO~ A/cm2 at 77 K and 6 x 106 A/cm2 at 4.2 K. The critical current density at 77 K will be controlled by the high 7~phase. The current will flow through the high-L~ current channel presented in the sputtered Bi—Sr—Ca—Cu—O films, since the films are composed of a mixture of the high 7~phase and the low 7~phase. More critical current density will be possible in the case of films composed of the high-7~ phase only. For the Tl—Ba—Ca~Cu—O films, the critical current density was found to be 8000 A/cm2 at 4.2 K. In summary, we have prepared c-axis oriented thin films of the superconducting Bi—Sr—Ca—Cu— O and Tl—Ba—Ca—Cu—O systems. Their zero resistance temperatures are higher than 100 K. Further
40
50
60
(deg)
Fig. 4. X-ray diffraction pattern of the Tl—Ba—Ca—Cu—O film on MgO.
research into deposition conditions should result in the formation of single phase and/or single crystal superconducting films. The authors thank Drs. S. Hayakawa and T. Nitta for their continuous encouragements and Drs. T. Mitsuyu, S. Kawashima, S. Hatta and M. Kitabatake for useful discussion.
References [1] H. Maeda, Y. Tanaka, M. Fukutomi and T. Asano. Japan. J. Appl. Phys. 27 (1988) L209. [2] Z.Z. Sheng and AM. Hermann, Nature 332 (1988) 138. [3] H. Koinuma, M. Kawasaki, S. Nagata, K. Takeuchi and K. Fueki, Japan. J. Appl. Phys. 27 (1988) L376. [4] M. Nakao, H. Kuwahara, R. Yuasa, H. Mukaida and A. Mizukami, Japan. J. AppI. Phys. 27 (1988) L378. [5] J.H. Kang, R.T. Kampwirth, K.E. Gray, S. Marsh and E.A. Huff, Phys. Letters, to be published. [61E. Takayama-Muromachi, Y. Uchida, A. Ono, F. lzumi, M. Onoda, Y. Matsui, K. Kosuda, S. Takekawa and K. Kato, Japan. J. Appi. Phys. 27 (1988) L365. [7] Y. Ichikawa, H. Adachi, K. Hirochi, K. Setsune, S. Hatta and K. Wasa, Phys. Rev. B, to be published. [8] R.M. Hazen, LW. Finger, Ri. Angel, CT. Prewitt, N.L. Ross, C.G. Hadidiacos, P.J. Heaney, DR. Veblen, Z.Z. Sheng, A. El Au and A.M. Hermann, Phys. Rev. Letters 60 (1988) 1657.
Journal of Crystal Growth 91(1988) 352—354 North-Holland, Amsterdam
SUPERCONDUCTING THIN FILMS OF Bi-Sr-Ca-Cu-O AND TI-Ba-Ca-Cu-O WITH 1~ABOVE 100 K Hideaki ADACHI, Kiyotaka WASA, Yo ICHIKAWA, Kumiko HIROCHI and Kentaro SETSUNE Central Research Laboratories, Matsushita Electric Industrial Co., Ltd., Moriguchi, Osaka 570, Japan Received 14 April 1988; manuscript received in final form 16 May 1988
Thin films of the Bi—Sr—Ca—Cu—O and Tl—Ba—Ca—Cu—O systems have been prepared on MgO substrates by RF-magnetron sputtering and subsequent annealing. These thin films showed a highly oriented structure with c axis perpendicular to the substrates. The Bi—Sr—Ca—Cu—O thin films exhibited superconducting transitions with the zero resistance temperature T~= 102 K and the 5 T1—Ba---Ca—Cu--O thin films hadsame 7~= order 100 K.ofThe critical as current density of thesystem. Bi—Sr—Ca—Cu—O thin films was as high as 2 X10 A/cm2 at 77 K, which was the magnitude the Ln—Ba—Cu—o
Thin films of the new high-7~oxide superconductors, Bi—Sr—Ca—Cu—O [1] and Ti—Ba—Ca— Cu—O [2], have recently received much attention, since the zero resistance temperature, 7~,is expected to be higher than 100 K. Attempts have been made to deposit thin films in the Bi—Sr—Ca—Cu—0 system by the sputtering. These experiments suggest that c-axis oriented thin films with 7~ 80 K can be successfully deposited on a crystalline substrate [3—5].The crystal structure corresponds to that of ceramics of the low 1~phase with the lattice constant c 30.6 A [6]. Occasionally, thin films with T~as high as 100 K were prepared using sputtering [7]. However, their crystal structure and superconducting properties are not well understood. In this paper we will describe the structural studies and superconducting properties of thin films of the Bi—Sr—Ca—Cu—0 and the Ti—Ba—Ca—Cu—O systern prepared by sputtenng deposition. Thin films of Bi compound and Tl compound were prepared by using an RF-planar magnetron sputtering system. Their targets were complex oxides of Bi—Sr—Ca—Cu and Ti—Ba—Ca—Cu, respectively. Typical sputtering conditions are shown in table 1. The Bi—Sr—Ca—Cu—O target was made by sintenng a mixture of Bi203 (99.999%), SrCO3 (99.9%), CaCO3 (99%) and CuO (99.9%) at 880°C =
for 8 h in air. The Ti—Ba—Ca—Cu—O target was made by sintering a mixture of Tl 203 (99.5%), BaCO3 (99.9%), CaCO3 (99%) and CuO (99.9%) at 910°Cfor 8 h in air. The as-sputtered films were postannealed at 850—900°C in 02 to improve their superconducting properties. Resistivity measurements were done using the standard DC four-probe method with gold electrodes deposited on the film surface. The critical current density was evaluated from the current— voltage characteristics. Thin films of the Bi compound were prepared at two substrate temperatures of 200 and 800°C. The sputtering targets were modulated to keep the film composition at 1—1—1—2 ratio of Bi—Sr—Ca— Cu within 10% accuracy. The annealing condition Table 1 Sputtering conditions Target
Complex oxide, 100~ Bi/Sr/Ca/Cu = 1.2—1.6/1/1—1.5/2 Tl/Ba/Ca/Cu = 2/1/2/3 Substrate (100) plane of MgO Substrate temperature 200 and 8000 C Sputtering gas Ar/02 = 1—1.5 Gas pressure 0.5 Pa RF input power 100—150 W Growth rate
0022-0248/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
50-80 A/mm
H. Adachi et al.
/
Superconducting thin films of Bi—Sr—Ca—Cu—O and Tl—Ba—Ca—Cu—O
(a)
—
spond to the high 7~phase of Bi—Sr—Ca—Cu—O with c = 36 A generally believed in the ceramics. These sputtered films showed the zero resistance ~H
0 ° C
H I
___ ..
I
j~l~_
_________________________________ 10
20
30 20
40 (deg I
50
60
10 ~.,
(b)
8
353
26
0
________________________________
to the ceramics temperature 7~= value 102 Kof(fig. 1052b), K which [1]. The wascrystal close structure of the sputtered Bi—Sr—Ca—Cu—O films with 7~= 102 K is not well understood. It is likely that the films are composed of a mixture of the high T~phase and the low 27~ phase. The high T~, phase may be segregated between the crystailites of the sputtered films of the low 7~phase and form current channels. Similar to the Bi—Sr—Ca—Cu—O system, thin films of Tl—Ba—Ca—Cu—O system were prepared by RF-magnetron sputtering. However, their chemical composition was quite unstable during the deposition and the postannealing process due to the high vapor pressure of Ti. Thin films were deposited without intentional heating of substrates (200°C) and annealed at 900°C for 30 mm in Tl
0 0
100 200 Temperature (K)
300
vapor. These annealed films showed a broad su-
Fig. 1. X-ray diffraction pattern and superconductivity of the Bi—Sr—Ca—Cu—O thin film deposited at 200°C and postannealed. The thickness is about 0.5 ~m.
was 890°C for 20 mm and subsequently 850—880°Cfor 5 h in oxygen atmosphere. Fig. 1 shows a typical X-ray diffraction pattern and re sistivity—temperature characteristic of a Bi—Sr— Ca—Cu—O thin film deposited at 200°C and postannealed. It is seen that the film has a highly oriented structure with c axis perpendicular to the substrate (fig. la). The lattice constant c is evaluated to be 30.64 A, which corresponds to the low 1~phase of Bi—Sr—Ca—Cu—O compound described for ceramics [6]. These thin films show the zero resistance temperature 7~= 70 K (fig. ib). The superconducting properties of the Bi—Sr— Ca—Cu—O thin films were strongly influenced by the substrate temperature in the deposition. Fig. 2 shows typical X-ray diffraction pattern and resistivity—temperature characteristics for the films deposited at 800°Cand postannealed. It is seen that the additional peaks are superposed on the periodical patterns of the low 7~phase at 20 = 24° and 34° (fig. 2a). The additional peaks may corre-
(a)
—
° C
~
~~
~
i~j~~
-__________________________________ 10
30
20
20
40
(degl
50
60
(b) o
a
~
2
.
1
0
0
0
200 300 (K) Fig. 2. X-ray diffraction pattern and superconductivity of the Bi—Sr—Ca—Cu—O thin film deposited at 800°C and postannealed. The thickness is about 0.2 ~sm. ‘
100
Temperature
354
H. Adachi et a!.
/ Superconducting thin films of Bi—Sr—Ca—Cu—O and
TI—Ba— Ca—Cu—O
2C
15 0
10 C
0~.
a
-
cc 0
100 Temperature
200
10
300
Fig. 3. Temperature dependence of the resistivity Tl—Ba—Ca—Cu—O thin film with 0.6 (im thickness.
20
30 20
(K)
for
perconducting transition at around 110 K and exhibited a zero resistance temperature I~= 100 K as shown in fig. 3. Fig. 4 shows the X-ray diffraction pattern of the Tl—Ba—Ca—Cu—O thin film, The periodical sharp peaks observed in the pattern indicate that the films are composed mainly of oriented structure. The main peaks can be assigned by the diffraction of material with lattice constant c = 36 A, as shown in the figure. This lattice constant c is close to the value reported in Tl—Ba—Ca—Cu—O ceramics [8]. The critical current density measured for the Bi—Sr—Ca—Cu—O films was as high as 2 X iO~ A/cm2 at 77 K and 6 x 106 A/cm2 at 4.2 K. The critical current density at 77 K will be controlled by the high 7~phase. The current will flow through the high-L~ current channel presented in the sputtered Bi—Sr—Ca—Cu—O films, since the films are composed of a mixture of the high 7~phase and the low 7~phase. More critical current density will be possible in the case of films composed of the high-7~ phase only. For the Tl—Ba—Ca~Cu—O films, the critical current density was found to be 8000 A/cm2 at 4.2 K. In summary, we have prepared c-axis oriented thin films of the superconducting Bi—Sr—Ca—Cu— O and Tl—Ba—Ca—Cu—O systems. Their zero resistance temperatures are higher than 100 K. Further
40
50
60
(deg)
Fig. 4. X-ray diffraction pattern of the Tl—Ba—Ca—Cu—O film on MgO.
research into deposition conditions should result in the formation of single phase and/or single crystal superconducting films. The authors thank Drs. S. Hayakawa and T. Nitta for their continuous encouragements and Drs. T. Mitsuyu, S. Kawashima, S. Hatta and M. Kitabatake for useful discussion.
References [1] H. Maeda, Y. Tanaka, M. Fukutomi and T. Asano. Japan. J. Appl. Phys. 27 (1988) L209. [2] Z.Z. Sheng and AM. Hermann, Nature 332 (1988) 138. [3] H. Koinuma, M. Kawasaki, S. Nagata, K. Takeuchi and K. Fueki, Japan. J. Appl. Phys. 27 (1988) L376. [4] M. Nakao, H. Kuwahara, R. Yuasa, H. Mukaida and A. Mizukami, Japan. J. AppI. Phys. 27 (1988) L378. [5] J.H. Kang, R.T. Kampwirth, K.E. Gray, S. Marsh and E.A. Huff, Phys. Letters, to be published. [61E. Takayama-Muromachi, Y. Uchida, A. Ono, F. lzumi, M. Onoda, Y. Matsui, K. Kosuda, S. Takekawa and K. Kato, Japan. J. Appi. Phys. 27 (1988) L365. [7] Y. Ichikawa, H. Adachi, K. Hirochi, K. Setsune, S. Hatta and K. Wasa, Phys. Rev. B, to be published. [8] R.M. Hazen, LW. Finger, Ri. Angel, CT. Prewitt, N.L. Ross, C.G. Hadidiacos, P.J. Heaney, DR. Veblen, Z.Z. Sheng, A. El Au and A.M. Hermann, Phys. Rev. Letters 60 (1988) 1657.