| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 87 === Lead-based ferroelectrics is very promising as a material for the next generation memory use. The purpose of this study is to investigate the film growth mechanism concerning the growth of three-component PbTiO3 and four-component Pb(Zr,Ti)O3 thin films by metalorganic chemical vapor deposition(MOCVD).
The precursors used to grow PbTiO3 were Pb(C2H5)4 and Ti(i-OC3H7)4. Without adding oxygen, only TiO2 films were obtained. The film changed to PbTiO3 after adding 1% volume concentration of oxygen at 550℃. In the same time, the rate-determining step changed from diffusion control to surface reaction control, which was attributed to the strong adsorption characteristics of Pb(C2H5)4 on substrate surface. Accordingly, an Eley-Rideal mechanism was proposed which considered a surface reaction including adsorbed Pb(C2H5)4 and adsorbed oxygen together with gaseous Ti(i-OC3H7)4 to react to form PbTiO3 films. The growth rate relation with respect to experimental parameters such as precursor concentration, oxygen concentration, and substrate temperature was in good agreement with the model.
The film grow of PbTiO3 on various oxide substrates showed that Pb(C2H5)4 played a dominant role. The partial charge concept was applied to explain the influence of the interreaction between Pb(C2H5)4 and substrate on film deposition.
The single-component Zr(t-C4H9)4 experiment showed that the precursor itslef can provide the required oxygen for ZrO2 growth. The rate-determining step is a surface reaction under 450℃, while it changed to diffusion controlled above 450℃, which was similar to Ti(i-OC3H7)4. When adding Zr(t-C4H9)4 into the three-component system, the activation energy obtained was 5.64 kcal/mol, which is quite close to PbTiO3 film growth in the temperature range 550 ~ 650℃. The result indicated that the surface reaction of Pb(C2H5)4 still played a dominant role in the four-component system as well.
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