Fabrication of BaTiO 3 Thin Films and Microdot Patterns by Halide-Free Nonaqueous Solution Route Hajime Wagata, z Takaaki Taniguchi, z Ruwan Gallage, z A. K. Subramani, z Naonori Sakamoto, y Tomoaki Watanabe, z Masahiro Yoshimura, z and Nobuhiro Matsushita w,z z Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama, Japan y Materials Science and Chemical Engineering, Faculty of Engineering, Shizuoka University, Hamamatsu, Japan z Department of Applied chemistry, School of Science and Technology, Meiji University, Tokyo, Japan This paper reports on the fabrication of barium titanate (BaTiO 3 ) thin films using a precursor solution containing Ba and Ti alkoxides. L-proline was used to prevent the precipitation of Ba and Ti alkoxides in a mixed solvent of ethanol and but- ylcarbitol under ambient conditions. Analysis of X-ray diffraction and Raman spectra revealed that the as-deposited amorphous film crystallized into a tetragonal BaTiO 3 phase after annealing at 6501C in air. Scanning electron microscopic observations showed that the BaTiO 3 film was free from cracks even after annealing and exhibited good adhesion to the substrate. Because the pre- cursor solution developed was sufficiently stable in air, dot pat- terning of BaTiO 3 was also performed using an inkjet system. I. Introduction B ARIUM titanate (BaTiO 3 ) thin films are widely applied as di- electric layers for capacitors, waveguides, and sensors. 1–3 To fabricate high-quality BaTiO 3 films, gas-phase processes such as sputtering, 4,5 pulse laser deposition, 6,7 and chemical vapor de- position 8,9 are generally used. However, these are complicated processes and require expensive equipments to deposit the film in an ultra-high vacuum. Spray pyrolysis has been intensively investigated as an alter- native preparative technique for metal oxide films. This method has a potential advantage in terms of the cost-effective produc- tion of the film, owing to the use of inexpensive materials, mod- erate reaction conditions, and the simplicity of the procedure, as well as simple experimental setups. Many types of functional ceramic films, such as tin oxides, zinc oxides, titanium oxides, lead zirconium titanate, and barium strontium titanate, have been prepared by spray pyrolysis. 10–13 However, in these previ- ous studies, metal chlorides or nitrates were generally used as metal sources and solvents. Hence, the fabricated film essentially contained a significant amount of halide and nitrate contami- nations, which probably degraded their properties. 14 In the former part of the present study, we developed a ‘‘ha- lide-free’’ spray pyrolysis technique for the deposition of BaTiO 3 films, wherein Ba and Ti alkoxides were stabilized by an amino acid, L-proline, in the precursor solution. In recent years, the patterning of functional oxide materials was achieved with the inkjet technique using alkoxide and or- ganometallic solutions. 15–18 In the latter part of the present study, BaTiO 3 microdots were fabricated by inkjet patterning to demonstrate the possibility of using the precursor solution as an ‘‘ink.’’ II. Experimental Procedure (1) Preparation of the Precursor Solution L-proline (99.9%, Sigma-Aldrich Japan Co., Shinagawa-ku, Tokyo, Japan), barium isopropoxide [Ba((CH 3 ) 2 CHO) 2 ] (Sigma- Aldrich Japan Co., 99.9%), titanium tetra isopropoxide [Ti- ((CH 3 ) 2 CHO) 4 ] (97.0%, Kanto Chemical Co. Inc., Chuou-ku, Tokyo, Japan), dehydrated ethanol (Wako Pure Chemical In- dustries Ltd., Japan, 99.5%) and 2-(2-butoxyethoxy) ethanol (98.0%, Wako Pure Chemical Industries Ltd., Chuo-ku, Osaka, Japan) were used as received. The experimental procedure is schematically illustrated in Fig. 1(a). First, an amount of L-pro- line was dissolved in dehydrated ethanol (100 mL) and then 0.01 mol of Ti((CH 3 ) 2 CHO) 4 and 0.01 mol of Ba((CH 3 ) 2 CHO) 2 were added, while stirring, to prepare a precursor solution con- taining 0.10M of both metal ions. Here, the concentration of L-proline was varied from 0.025 to 0.10M to determine the optimum condition. Finally, the solution was ten times diluted with a 1:1 solution of dehydrated ethanol and 2-(2-butoxy- ethoxy) ethanol for spray pyrolysis and inkjet patterning. Precursor powder was prepared by evaporating the precursor solution in a vacuum desiccator to study the thermal decompo- sition behavior. (2) Film Fabrication by Spray Pyrolysis Figure 1(b) shows a schematic illustration, and Table I repre- sents the experimental conditions of spray pyrolysis for fabri- cating films. Films were fabricated by spraying the precursor solution onto a glass substrate (#7059, Corning Inc., Minato-ku, Tokyo, Japan) maintained at 3501C on a hot plate. Substrates were ultrasonically cleaned in ethanol before deposition. Sixty spray cycles, with each cycle consisting of 8 s of spray time, were used. To maintain the substrate temperature, a 1 min interval was maintained between each spray cycle. The as-deposited films were subsequently annealed at 4501, 5501, and 6501C for 4 h at a heating rate of 101C/min in an electric furnace. (3) Inkjet Patterning The inkjet patterning equipment (GM02-001/IJP, Global Ma- chinery Co. Ltd., Hadano city, Kanagawa, Japan) used in this study is schematically illustrated in Fig. 1(c). Successive pattern- ing was performed by jetting droplets of the precursor solutions through a piezoelectric inkjet nozzle head (MJ-AB-01-60, Micro Fab Technologies Inc., Suite 110 Plano, TX) with an orifice diameter of 60 mm onto corning glass substrates heated at 1501C. In order to eject uniform droplets, a 65 V unipoler pulse lasting 50 ms at a frequency of 1 kHz was applied to the piezo- electric nozzle. Ten droplets of the precursor solution were shot successively at the same position to form one dot. Microdot ar- rays with matrix size of 5 Â 5 dots were annealed at 6501C for N. Alford—contributing editor w Author to whom correpsondence should be addressed. e-mail: matsushita.n.ab@m. titech.ac.jp Manuscript No. 25647. Received December 16, 2008; approved August 12, 2009. J ournal J. Am. Ceram. Soc., 93 [2] 381–386 (2010) DOI: 10.1111/j.1551-2916.2009.03383.x r 2009 The American Ceramic Society 381