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Preparation of transparent and conducting indium oxide films by solution pyrolysis of dibutylindium thiolate
Thin Solid Films, 167 (1988) L27-L29
L27
Letter Preparation of transparent and conducting indiam oxide iilms by solution pyrolysis of dibutylindium tldolate RYOKI NOMURA, AKIKO MORITAKE, KOUICHI KANAYA AND HARUO MATSUDA
Department of Applied Chemistry, Faculty of Engineering, Osaka University, YamaabOka. Suita, Osaka 565 (Japan) (Received July 28,1988; accepted September 21,1988)
Thin indium oxide films are most. attractive materials for transparent conductors and display panels etc. I. Although several procedures have already been reported for the preparation of indium oxide thin films, chemical processes such as spray pyrolysisz4, the dip-dry methodsv6, printing ‘-lo and chemical vapour deposition”*” are known to be most convenient and useful for the production of large area films. However, these chemical processes must usually be carried out with substrate temperatures greater than 500°C in order to obtain highly conductive films. In a previous paper, we have reported the limited success in lowering the process temperature for the preparation of indium tin oxide films by using oxygen-containing organoindium compounds such as butylindium acylates and alkoxides13. In this paper, we will propose that a solution pyrolysis of the sulphur-containing organoindium precursor and the successive sulphide-oxide conversion process could effectively reduce the process temperature in the printing method. A typical preparation procedure of indium oxide films is as follows. A solution of diisobutylindium isopropylthiolate ((CH,),CHCH,InSCH(CH,),, Bu’,InSPr’) in p-xylene (10-15 wt. %) was dropped onto a glass substrate (Iwaki, WSLID-P2926 76 mm x 26 mm) and spread over the surface by tipping. The substrate was heated in a quartz tube (40 mm in diameter) at 200 “C for 1 h under pure argon and then annealed at 300-500 “C for 1 h. The annealing was carried out under air, N, and At--O2 (99.9% Ar-O.l% 0,). The resulting indium oxide films were characterized by X-ray diffraction, scanning electron microscopy (SEM) and UV-visible spectra. The resistivities were measured by a d.c. four-probe apparatus. Thermal decomposition of the sulphur-containing organoindium compounds such as Bu’JnSPr’ occurred at below 250 “C and gave indium sulphide (Ins) as a pyrolysate. In contrast, we have reported l3 that the oxygen-containing organoindium compounds decomposed at 350400°C. Thus, it can be said that the replacement of oxygen with sulphur in the precursor reduced the decomposition temperature to the extent of more than lOO-150°C. The solution pyrolysis of BuizInSPri in p-xylene was conducted at 200 “C for 1 h under a pure argon atmosphere and homogeneous InS films were obtained. A typical X-ray diffraction pattern of such an InS film is shown in Fig. 1, spectrum A. Then the annealing of the 004@6090/88/$3.50
0 Elsevier Sequoia/Printed
in The Netherlands
L28
LIDTJIRS
20
30
LO
50
28, degree Fig. 1. X-ray diffraction patterns of InS and In,O, films formed on glass substrate-sby the solution pyrolysis and successive sulphur-xygen conversion method using Bu’,InSPr’ as a precursor: spectrum A, InS films obtained at 200 “C for 1 h under argon atmosphere; spectrum B, after annealing the InS film at 375 “C for 1 h under argon (containing 0.1%oxygen).
InS films under air, N, and argon (containing 0.1% oxygen) was carried out and it was found that the oxidation of’InS into In,O, effectively occurrred as shown in Fig. 1, spectrum B. Although the indium oxide films obtained under air and N, were somewhat opaque and resistive, transparent and conductive indium oxide films could only be obtained by annealing under an argon (containing 0.1% 0,) atmosphere. The resistivity pn decreased steeply with temperature rising in the range 300-375 “C and p. reached 8.2 x 10m3 R cm at 375 “C as shown in Fig. 2. In the range of annealing temperatures of 40&500 “C, pI1remained at an almost constant value (of the order of lo- 3 R cm) and seemed not to be affected by the annealing temperature, in contrast with the reported chemical process I4 . However, the lowest ps value was exhibited in the specimen obtained at 500°C (6.6 x 10e3 Qcm). Further, the average transmittance of such indium oxide films exceeded over 90 % in the region 400-900 nm.
I 3m
400
so0
Tsl’C
Fig. 2. Correlation between resistivity p, and annealing temperature.The film thickness was determined from SEM cross-sectional profiles (SO-100nm).
LETTERS
L29
In conclusion, transparent (better than 90% in the visible region) and conductive (p, x lo- 3 R cm) indium oxide films were prepared by solution pyrolysis of a sulphur-containing organoindium precursor such as Bu’JnSPr’ to give InS films and a successive sulphur-oxygen conversion process (annealing) even at 375 “C under argon (containing 0.1% 0,). 1 2 3 4 5 6 7 8 9 10 11 12 13 14
K. L. Chopra, S. Major and D. K. Pandya, Thin Solid Films, 102 (1983) 1. S. Kulaszewicz, W. Jarmoc, I. Lasocka and Z. Lasocki, Thin Solid Films, 148 (1987) L55. M. G. Mikailov, T. M. Ratcheva and M. D. Nanova, Thin SolidFilms, 146 (1987) L23. J. C. Manifacier ad J. P. Fillard, Thin Soild Films, 77 (1981) 67. S. Hagihara and K. Kinugawa, Yogyo Kyokui-Shi, 90 (1982) 9. H. Dislich, Glustech. Ber., 57 (1984) 229. H.-J. Gaeser, Glustech. Ber., 50 (1977) 266. A. Tsunashima, T. Asai, K. Kodaira and T. Matsushita, Chem. L.&z.,(1978) 855. E. Kawabata and K. Oshima, Jpn. J. Appl. Phys., 18 (1979) 205. H. B. Saim, D. S. Campbell and J. A. Avaritsioitis, Sol. Energy Mater., I3 (1986) 85. M. Privman, J. Berger and D. D. Tannhauser, Thin Solid Films, IO2 (1983) 117. D. E. Carlson, J. Electrochem. Sot., 122 (1975) 1334. R. Nomura, S.-J. Inazawa, H. Matsuda and S. Saeki, Polyhedron, 6 (1987) 507. K. Kaneyasu, K. Adachi, T. Hirayama and H. Sakata, Denki Kugakv, 55 (1987) 245.
L27
Letter Preparation of transparent and conducting indiam oxide iilms by solution pyrolysis of dibutylindium tldolate RYOKI NOMURA, AKIKO MORITAKE, KOUICHI KANAYA AND HARUO MATSUDA
Department of Applied Chemistry, Faculty of Engineering, Osaka University, YamaabOka. Suita, Osaka 565 (Japan) (Received July 28,1988; accepted September 21,1988)
Thin indium oxide films are most. attractive materials for transparent conductors and display panels etc. I. Although several procedures have already been reported for the preparation of indium oxide thin films, chemical processes such as spray pyrolysisz4, the dip-dry methodsv6, printing ‘-lo and chemical vapour deposition”*” are known to be most convenient and useful for the production of large area films. However, these chemical processes must usually be carried out with substrate temperatures greater than 500°C in order to obtain highly conductive films. In a previous paper, we have reported the limited success in lowering the process temperature for the preparation of indium tin oxide films by using oxygen-containing organoindium compounds such as butylindium acylates and alkoxides13. In this paper, we will propose that a solution pyrolysis of the sulphur-containing organoindium precursor and the successive sulphide-oxide conversion process could effectively reduce the process temperature in the printing method. A typical preparation procedure of indium oxide films is as follows. A solution of diisobutylindium isopropylthiolate ((CH,),CHCH,InSCH(CH,),, Bu’,InSPr’) in p-xylene (10-15 wt. %) was dropped onto a glass substrate (Iwaki, WSLID-P2926 76 mm x 26 mm) and spread over the surface by tipping. The substrate was heated in a quartz tube (40 mm in diameter) at 200 “C for 1 h under pure argon and then annealed at 300-500 “C for 1 h. The annealing was carried out under air, N, and At--O2 (99.9% Ar-O.l% 0,). The resulting indium oxide films were characterized by X-ray diffraction, scanning electron microscopy (SEM) and UV-visible spectra. The resistivities were measured by a d.c. four-probe apparatus. Thermal decomposition of the sulphur-containing organoindium compounds such as Bu’JnSPr’ occurred at below 250 “C and gave indium sulphide (Ins) as a pyrolysate. In contrast, we have reported l3 that the oxygen-containing organoindium compounds decomposed at 350400°C. Thus, it can be said that the replacement of oxygen with sulphur in the precursor reduced the decomposition temperature to the extent of more than lOO-150°C. The solution pyrolysis of BuizInSPri in p-xylene was conducted at 200 “C for 1 h under a pure argon atmosphere and homogeneous InS films were obtained. A typical X-ray diffraction pattern of such an InS film is shown in Fig. 1, spectrum A. Then the annealing of the 004@6090/88/$3.50
0 Elsevier Sequoia/Printed
in The Netherlands
L28
LIDTJIRS
20
30
LO
50
28, degree Fig. 1. X-ray diffraction patterns of InS and In,O, films formed on glass substrate-sby the solution pyrolysis and successive sulphur-xygen conversion method using Bu’,InSPr’ as a precursor: spectrum A, InS films obtained at 200 “C for 1 h under argon atmosphere; spectrum B, after annealing the InS film at 375 “C for 1 h under argon (containing 0.1%oxygen).
InS films under air, N, and argon (containing 0.1% oxygen) was carried out and it was found that the oxidation of’InS into In,O, effectively occurrred as shown in Fig. 1, spectrum B. Although the indium oxide films obtained under air and N, were somewhat opaque and resistive, transparent and conductive indium oxide films could only be obtained by annealing under an argon (containing 0.1% 0,) atmosphere. The resistivity pn decreased steeply with temperature rising in the range 300-375 “C and p. reached 8.2 x 10m3 R cm at 375 “C as shown in Fig. 2. In the range of annealing temperatures of 40&500 “C, pI1remained at an almost constant value (of the order of lo- 3 R cm) and seemed not to be affected by the annealing temperature, in contrast with the reported chemical process I4 . However, the lowest ps value was exhibited in the specimen obtained at 500°C (6.6 x 10e3 Qcm). Further, the average transmittance of such indium oxide films exceeded over 90 % in the region 400-900 nm.
I 3m
400
so0
Tsl’C
Fig. 2. Correlation between resistivity p, and annealing temperature.The film thickness was determined from SEM cross-sectional profiles (SO-100nm).
LETTERS
L29
In conclusion, transparent (better than 90% in the visible region) and conductive (p, x lo- 3 R cm) indium oxide films were prepared by solution pyrolysis of a sulphur-containing organoindium precursor such as Bu’JnSPr’ to give InS films and a successive sulphur-oxygen conversion process (annealing) even at 375 “C under argon (containing 0.1% 0,). 1 2 3 4 5 6 7 8 9 10 11 12 13 14
K. L. Chopra, S. Major and D. K. Pandya, Thin Solid Films, 102 (1983) 1. S. Kulaszewicz, W. Jarmoc, I. Lasocka and Z. Lasocki, Thin Solid Films, 148 (1987) L55. M. G. Mikailov, T. M. Ratcheva and M. D. Nanova, Thin SolidFilms, 146 (1987) L23. J. C. Manifacier ad J. P. Fillard, Thin Soild Films, 77 (1981) 67. S. Hagihara and K. Kinugawa, Yogyo Kyokui-Shi, 90 (1982) 9. H. Dislich, Glustech. Ber., 57 (1984) 229. H.-J. Gaeser, Glustech. Ber., 50 (1977) 266. A. Tsunashima, T. Asai, K. Kodaira and T. Matsushita, Chem. L.&z.,(1978) 855. E. Kawabata and K. Oshima, Jpn. J. Appl. Phys., 18 (1979) 205. H. B. Saim, D. S. Campbell and J. A. Avaritsioitis, Sol. Energy Mater., I3 (1986) 85. M. Privman, J. Berger and D. D. Tannhauser, Thin Solid Films, IO2 (1983) 117. D. E. Carlson, J. Electrochem. Sot., 122 (1975) 1334. R. Nomura, S.-J. Inazawa, H. Matsuda and S. Saeki, Polyhedron, 6 (1987) 507. K. Kaneyasu, K. Adachi, T. Hirayama and H. Sakata, Denki Kugakv, 55 (1987) 245.