| Summary: | 博士 === 輔仁大學 === 應用科學與工程研究所博士班 === 100 === Co inserted layer with thickness varied from 0 to 20 nm on the dielectric permittivity of Ta2O5、SiO2 and BaTiO3 films fabricated on glass B270 substrates by the reactive sputtering technique was studied. The variation of dielectric constant for films which is dependent on the thickness of the Co inserted layer were measured from 150 kHz to 30 MHz. The dielectric constant is around 7.4~7.6 for Ta2O5/B270、SiO2/B270、BaTiO3/B270 films and B270 glass substrate. However, it is rapidly raised up for all the samples of trilayer thin films with the thickness of Co inserted layer larger than 2 nm. This enhancement behavior of the dielectric constant could be explained by the growth mechanism of the Co inter-layer from island clusters to continuous Co layer for samples with x larger than 2 nm. For studying the growth mechanism of the Co inserted layer, we fabricated bilayer samples with Co/SiO2、Co/ Ta2O5 and Co/ BaTiO3 structures, and an atomic force microscope (AFM) was used to study the surface morphology roughness behavior. The roughness increases with increasing the thickness of Co layer roughly below 2 nm. After the pick value for samples with 2 nm Co, the roughness decreases with increasing the thickness. This is related to the formation of a continuous Co layer on top layer after the thickness of Co layer is larger than 2 nm. For identifying the cross section of the samples with Co inserted layer, a transmission electron microscope (TEM) was used. The cross section TEM pictures for samples show cluster andcontinuous distribution of the morphology of the inserted Co layer in trilayer thin films. From both the AFM and TEM investigations, we demonstrate experimentally that the enhancement of the dielectr ic constant is related to the formation of a continuous Co inserted layer for samples with x larger than 2~3 nm. In other words, the adding of a Co inserted layer in Ta2O5、SiO2 and BaTiO3 films will redistribute the interface charges owing to the Maxwell-Wagner mechanism, and therefore will enhance both the intrinsic polarization and its dielectric constant of these films. When applying a magnetic field parallel to the films, a 0.02 ~ 0.80 % variation in the dielectric constant for samples with x larger than 1~2 nm was experimentally observed. This increase behavior is roughly saturated under an applied magnetic field roughly above 40~60 Oe. From this study, the magnetodielectric properties in trilayer thin films are manifested and it has potential for a ferroic sensor application.
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