| Summary: | 碩士 === 國立清華大學 === 材料科學工程學系 === 89 === Abstract
The BaxSr1-xTiO3 and Al-doped BST thin films were fabricated on Pt/TaN/SiO2/Si and Al2O3 substrates using sol-gel technique. The structure and thermal decomposition were investigated by means of thermogravimetric/differential thermal analysis (TG/DTA), Fourier transform infrared spectroscopy and X-ray diffractometer (XRD) analysis. The composition and chemical states of elements in BST thin films were characterized using X-ray photoelectron spectroscopy (XPS) technique. The results of thermal decomposition indicated that most of the organics such as acetate and carbonate decomposed below 420oC. The perovskite structure formed above 450oC. The convoluted spectrums of XPS patterns revealed that the chemical states of Ba, Sr, Ti and O are Ba2+, Sr2+, Ti4+ and O2-, respectively. The convoluted Ba photoelectron spectrum showed two different Ba bonding types, the typical BST mode and a relaxation-related mode. The oxygen photoelectron spectrum consisted of the normal perovskite peak and two high energy components which were due to the surface contaminations.
Aluminum was introduced to depress high leakage current due to the surface roughness of Al2O3 substrate. The doped Al substitute Ti-sites of BST perovskite structure. Two possible current transport mechanisms including Schottky emission and Poole-Frenkel emission are employed to explain the current characteristics of BST thin films. The different dominant conduction mechanisms are dependent on the electric field and the surface roughness of the substrates. The barrier heights of Schottky and Poole-Frenkel emission at forward bias are both higher than those at reverse bias, which may be attributed to the different roughness of pre-layers. The Al-doped BST thin films exhibit finer grains on the basis of XRD patterns and FESEM observations and higher potential barrier, thus leakage current is reduced.
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