Vol.1 No.2 2008

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Research paper : The aerosol deposition method (J. Akedo et al.)−122 Synthesiology - English edition Vol.1 No.2 (2008) there are several issues that must be tackled including facility cost, energy consumption, and environment load to realize a mass production level. Making breakthroughs to solve these issues will be important. Therefore, construction of on-demand manufacturing process and system that can address these needs is expected to become important in the future from the perspectives of strengthening industrial competitiveness and reducing environment load. Investigations of such issues are made using small-scale cell production systems at assembly level including implementation of circuit substrate for sensor device[1].In the background of high performance device manufacturing described above, the R&D stance of not only “How do we realize the function?” but also “How should it be made to ensure resources and low costs?” will become more important. In this paper, the potential for on-demand manufacturing process based on aerosol deposition method is investigated along this stance.2 The aerosol deposition (AD) methodThe aerosol deposition method (hereinafter AD method)[2] is a technology in which fine or ultra-fine powder is mixed with gas to form an aerosol, that will be sprayed through a nozzle to form a film coat on a substrate. The motion energy of material particle accelerated by gas carrier is converted to local heat energy by colliding with the substrate, and substrate-particle and particle-particle bonds are achieved. However, the mechanism of energy conversion has not been sufficiently understood.Figure 1 shows the basic structure of the coating device. The device is composed of an aerosol generator connected to a narrow delivery tube and a coating chamber, which is vacuumed to 50~1 kPa using a vacuum pump. The dried fine or ultra-fine powder that makes the raw material is stirred and mixed with gas in the aerosol generator chamber, carried to the coating chamber by gas flow caused by pressure difference between the two chambers, accelerated through the slit nozzle, and sprayed onto the substrate. Normally, mechanically grounded sintered ceramic powder with particle diameter 0.08~2 µm is used as raw material. The gas carrying the ultra-fine powder can be easily accelerated to several hundreds m/sec by passing through a nozzle with micro opening of 1 mm or less. Since coating speed and density of film coat depends greatly on particle diameter, aggregation state, and dryness of ceramic fine powder, crushing and sorting devices are installed between the aerosol generator and the coating chamber to ensure high quality powder flow.Recently, using ceramic powder in AD method and selecting appropriate coating condition as well as adjusting particle diameter and its mechanical properties, room temperature impact consolidation (RTIC) was observed. This is a phenomenon where high density, transparent ceramic film was formed at room temperature at high speed, as shown in Figure 2[2][3]. The substrate was not heated when the powder material was sprayed onto the substrate, and no heat processing was required after coating. This phenomenon occurred not only for ceramic materials but was also observed for metals.Amorphous layer or heterophase between crystalline particles in the microstructure of ceramic film formed by RTIC using the AD method was not observed and the dense films obtained at room temperature consist of non-oriented microcrystal with size 10~20 nm or less. Clear lattice image has been observed in microcrystals 10 nm or less in diameter. Although some distortion occurred in the interior of the film, the texture of the films remained the same from substrate interface to film surface. The powders used in AD deposition have monocrystalline structures with average particle diameter 80~100 nm or more; however, smaller fine crystal texture was observed in the coated films. From the results of XRD and EDX analyses, the coated film maintained the crystal structure of material powder with small compositional variations. From measurement of particle speed and assessment of motion energy, it is considered that the material powder crystals are mechanically crushed by collision, become finer by plastic deformation, and nanocrystal thin film is formed as bonds between particles[1]-[3]. These are not seen in the conventional coating method using particle collision.Compared with the conventional thin film processes, the AD method shows the following unique characteristics:1. Binderless, dense coating/film are obtained at room temperature;2. High coating rate of 5~50 µm/min (conventional method: 0.01~0.05 µm/min);3. Film coat of same composition and crystal structure as powder used for complex composition system can be obtained with substantially different pressure;4. Wide variation of film thickness can be obtained (0.5 µm~1 mm);5. Without etching process, micro pattern can be obtained using direct rendering, mask method, or lift-off method;PZT thick film (500 µm)α-AI2O3(4 µm)Pt/Ti/SiO2/Si substrateFig. 2 Ceramic film created at room temperature using the AD method.(50)−

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