697 Fig. 1. Diagram of MIMIC for suspension of low solids loading. 697 Journal of the Ceramic Society of Japan 115 [11] 697–700 (2007) Paper i~êÖÉpÅ~äÉ m~ííÉêåáåÖ çÑ qál O k~åç mçïÇÉêë rëáåÖ jáÅêç jçäÇë Junko IMASU and Yoshio SAKKA Nano Ceramics Center, National Institute for Materials Science, 1–2–1, Sengen, Tsukuba, Ibaraki 305–0047 For the fabrication of ceramic micro-scale patterns over a wide area, the Micro-molding in Capillaries MIMIC method is can be used by applying low solid loading colloidal suspensions of nanopowders. However, to uniformly form thick films from low solids loading suspensions, it is necessary that the additional spontaneous process of concentrating the suspensions in the molds occurs and is successfully accomplished, after the ordinary MIMIC process caused by capillary action. This concentration of suspension occurs as a result of inflow of the suspension from the entrance along with solvent evaporation from the exit of the mold. Therefore, the suspen- sion preparation is important in order that the particles flow in due to the flow of the solvent. In this study, we determined the required condition of the suspension preparation by fabricating films from aqueous and ethanol- based suspensions of TiO2 nanopowders. By comparing the uniformity of the fabricated films and the particle distributions of the suspensions, it was found that the condition required for uniform patterning over a wide area is to disperse the nanoparticles into their primary size. =Received August 15, 2007; Accepted September 20, 2007? Key-words : Patterning, Micro mold, Nanoparticle, Titania, Suspension, Infiltration 1. Introduction According to recent miniaturization and integration of electro-devices, the development of easy and low-cost tech- niques for accurate fabrication of various ceramic micro-scale patterns is now occurring. The Micro-molding in Capillaries MIMIC method, 1 which is one of soft-lithography tech- niques, 2 is considered the technique that can fulfill these requirements. The soft-lithography techniques are a family of processes to fabricate accurate nano and micro-scale patterns using patterned elastomeric blocks for stamps or molds, which were introduced by the Prof. Whitesides' in the 1990s. They have advantages that their procedures are easy and of low cost because no special equipment is needed, and the fabricated patterns are accurate just like the mold pattern. Thus these techniques are widely applied in both industrial and biological fields. 3 The MIMIC process involves spontaneous infiltration into molds caused by capillary action. Therefore, various fluids such as polymers, solutions and so on, can be applied if only they satisfy the conditions which include a low viscosity and high wettability to the materials of the molds. 4 Besides, thick structures can be fabricated using deep molds. Ceramic pat- terning using the MIMIC process is now being mainly studied using 2 types of approaches. One uses the precursors for a sol–gel or polymer. As the starting materials that easily infiltrate by capillary action, this process is utilized for electro and optic devices. The other approach uses colloidal suspen- sions. 5–7 This process using a colloidal suspension has the following notable advantages: The shrinkage of the fabricated films is small because there is no organic residue, and this process is applicable for various ceramics available as pow- ders. Therefore, the MIMIC process using colloidal suspen- sions can be utilized for the fabrication of ceramic micro-scale patterning for various kinds of devices. However, when applying ceramic colloidal suspensions to the MIMIC process, the high viscosity of the suspension is a concern. When the suspension infiltrated by capillary action and form structures, the suspension must have only a few tens of solids loading. Such a suspension has a high viscosity and plastic flow. Furthermore, the viscosity soon increases because the suspension is concentrated by evaporation of the solvents during the process. As the infiltration speed is inversely proportional to the viscosity during the capillary action, 4 the infiltration is very slow and soon stops. Therefore, the infiltra- tion time becomes very short. We have been developing a technique to fabricate uniform micro-scale patterns over a wide area by the MIMIC process using ceramic colloidal suspensions. We used a few solids loading suspensions to take advantage of their low viscosity and Newtonian rheological characterizations for the wide area patterning. Figure 1 shows a diagram of the MIMIC process using low solids loading suspensions. This process occurs as follows: A micro-mold is attached to a substrate, and the suspension is poured into a suspension pool at the entrance of the mold. After the suspension spontaneously infiltrates and dries, we peel off the mold and get a patterned film the same as the mold pattern. Different from the molds of the ordinary MIMIC process, our mold has a suspension pool at the entrance side of the channels in order maintain a large amount of the low solids loading suspension. When we use a low solids loading suspension with a low viscosity, a wide area