Study on the stress generation during gel/ceramic thin film conversion

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1 Silica and titania gel films were deposited on silicon wafers by sol-gel method using alkoxide-derived sols as the coating solutions. The gel films were heated at constant rates in an infrared furnace up to 800℃, and in situ observation was made using an optical microscope. The cracking was found to occur during the heating-up stage, and the cracking onset temperature was lower than that of crystallization. The cracking onset temperatures were found to decrease with increasing initial film thickness and with decreasing heating rate.2 BaTiO_3 thin films were deposited on silica glass and MgO single crystal substrates by sol-gel dip-coating using an alkoxide solutions containing polyvinylpyrrolidone (PVP) as the coating solution. SEM observation revealed that the fihns deposited on the silica glass substrates have microcracks propagating along grain boundaries. On the other hand, no microcracks were found on the films deposited on the MgO single crystal substrates, The microcracks obse … More ived are supposed to be formed by tensile stress in films, which is thought to be generated as a result of the thermal expansion coefficient mismatch between the film and the substrates.3 Titania thin fihns were deposited on silica glass substrates by sol-gel method using alkoxide solutions containing diethanolamine, acetylacetone or acetic acid as the chelating agents. The stress in the fired films were measured by measuring the substrate bending, and the effect of the chelating agent on the stress. The stress was tensile, increasing in the order of acetic acid < acetylacetone < diethanolarnine. The effect of the chelating agent on the stress was interpreted in terms of the difference in the degree of film densification.4 BaTiO_3, Fe_2O_3 and PZT thin films were deposited on silica glass substrates using alkoxide or metal salt solutions containing PVP as the coating solutions. The critical thickness, the maximum thickness achievable without cracking via single-step deposition was found to increase by incorporating PVP in solutions, showing maximum around mole ratios of PVP/Ti(OC_3H_7^i)_4 = 0.5, PVP/Fe(N0_3)_3 = O and PVP/ (Ti(OC_3H_7^i)_4 + Zr(OC_3H_7^n)_4) for BaTiO_3, Fe_2O_3 and PZT films, respectively. Less