Indium-tin oxide thin films by metal-organic decomposition
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l n 2 0 3 - S n 0 2 films were produced by thermal decomposition of a deposit which was dip coated on borosilicate glass substrates from an acetylacetone solution of indium and tin acetoacetonate. Thermal analysis showed complete pyrolysis of the organics by 400 °C. The thermal decomposition reaction generated acetylacetone gas and was found to be first order with an activation energy of 13.6 Kcal/mole. Differences in thermal decomposition between the film and bulk materials were noted. As measured by differential scanning calorimetry using a 40 °C/min temperature ramp, the glass transition temperature of the deposited oxide film was found to be —462 °C, and the film crystallization temperature was found to be —518 °C. For film fabrication, thermal decomposition of the films was performed at 500 °C in air for 1 h followed by reduction for various times at 500 °C in a reducing atmosphere. Crystalline films resulted for these conditions. A resistivity of — 1.01 X 10" 3 O • cm, at 8 wt. % tin oxide with a transparency of —95% at 400 nm, has been achieved for a 273 nm thick film.
I. INTRODUCTION Ceramic films are important for optical and protective coatings, and are becoming increasingly important in the production of electronic devices. For many of these coating applications, films can be deposited from metal-organic solutions. Indium-tin oxide (ITO) films are useful for electrical contacts as well as antireflective coatings because they combine high transparency (>87%) with low resistivity ( In(C 5 H 7 O 2 ) 3 + 3HNO 3 + 2H 2 O SnCl 4 + 2C 5 H 8 O 2 -^ Sn(C 5 H 7 O 2 ) 4 + 4HC1 After distillation, these starting solutions are chelates of acetylacetone with the indium probably in a bipyramid bonding configuration with each acetylacetonate CD CO
3200
2790
2380
1970 1560 WfWENUMBER
1150
710
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330
FIG. 2. FTIR spectrum of indium acetylacetonate solution.
J. Mater. Res., Vol. 8, No. 12, Dec 1993 http://journals.cambridge.org
800
WAVELENGTH (nm)
3137 IP address: 155.37.205.36
D. Gallagher ef a/.: Indium-tin oxide thin films by metal-organic
decomposition
CH3
CH3
S
rr o en m
3500
30*0
2580
2120 1660 WfiVENUMBER
1200
7>tO
280
FIG. 3. FTIR spectrum of tin acetylacetonate solution.
complexing two of the six bonding sites and the tin in a sp3 tetrahedral bonding configuration with the four bonding sites occupied by the acetylacetonate, as presented in Fig. 4. These structures have not been independently confirmed. The distillation step served to remove water, nitric acid, and hydrochloric acid from the stock solutions
CH3
(a)
TABLE I. Frequencies and band assignments for indium and tin acetylacetonate complexes.
CH3
Vibrational frequencies (cm) ' Indium 3078 2997 2961 2919 1580} 1573 J 1556 1527 1442 1421} 1402 J 1370 1266 1197 1022 930
Tin
Band assignments
3065 Buried 2974 2924 ,
v(CH) vas methyl
1567
v(C— C) + v(C— O)
1531
Combination v(C—O) + v(C—C)
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