Microstructure and Crystallization Behavior of Sol-Gel Prepared BaTiO 3 Thin Films
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RESULTS AND DISCUSSION Effects of Water of Hydrolysis Figure 1 shows TEM bright field images and corresponding XRD patterns for BaTiO3 heat
treated at 6000 C for 3 hours in 02. Both films are polycrystalline, randomly oriented, and porous BaTiO3. The film with the higher water content (Fig. lb) has a grain size of 25-50 nm. In contrast, the film with no added water (Fig. la) has regions with a grain size of 25-50 nm surrounded by regions with grains of 5-15 nm. The TEM diffraction pattern from the fine grained region (Fig. l a) shows the presence of a second phase (most intense diffraction ring indicated by arrow) not seen in the XRD results. The phase matched with BaSrSi2O6, JCPDS card #20-143. The second phase may be a barium silicate phase, isostructural with the barium strontium silicate phase since Ba and Sr are substitutional in solid solution. Traces of this second phase were also found in other films deposited on (100) Si. Films with h=0 and h=2 were also heat treated at 7501C for 1 hour in 02. Like in the 600'C heat treatment, the films were polycrystalline, randomly oriented, and porous BaTiO3. The films had a grain size in the range of 25-50 nmi, with a slightly larger grain size in the films having the higher water content. Figure 2 shows a cross-section TEM micrograph of a film with h=2 on (100) Si heat treated at 7501C for 1 hour. A uniform amorphous SiO 2 layer with a thickness of 510 nmi formed at the interface between the Si and BaTiO3 (indicated by arrows). The film is crystalline BaTiO3 with the exception of a 20-50 nm region next to the Si02 interface. la 600-C, 3h
h=O
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FIGURE 1. - TEM micrographs and XRD patterns of BaTi03 thin films on (100) Si heat treated at 600 0 C for 3 hours in 02: (a) h=0,; (b)h=2.
650
70
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50 nm
FIGURE 2. - Cross-section 0TEM micrograph of BaTiO3 thin film with h=2 on (100) Si heat treated at 750 C for 1hour in 02. Arrows indicate amorphous Si02 interfacial layer.
EffecsLfHet ratmntn Rapid thermal annealing (RTA) was done at 700'C for 1minute in an effort to densify the films and miAnimize the amorphous interfacial layer. Films heat treated by RTA were found to be porous as were the films heat treated by conventional furnace annealing (CFA). The only difference between the microstructures was that the RTA films had slightly finer grains than the CFA films. The RTA films had a grain size on the order of 15-40 nmn, whereas the CFA samples had a grain size of 25-50 nm. In preliminary cross-section TEM analysis of the RTA film, it appeared that the film had fully crystallized even in regions near the interface. Effects of Substrate
Films were deposited on Ge coated (100) Si to study the effects of the substrate on the final films with h=0O deposited on microstructure of the film. Figure 3 shows TEM micrographs of (100) Si and Ge coated (100) Si substrates and heat treated at 750 0C for 1 hour in 02. The films have similar microstructures.
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