Study On The Processing And Properties Of Bi-based Oxide Films Grown By Atomic Layer Deposition

Bismuth atom has a series of unique physical and chemical properties attributed to its 6s2 lone pair electrons and the double bonding characteristics(covalent bonds and metal bonds).Furthermore,oxides are the most common class of compounds that exist in nature.Consequently,it is of great significance to carry out researches on bismuth oxides.From the component point of view,the binary Bi2O3 has the properties of wide bandgap,high refractive index,optical nonlinearity and so forth,making it widely used in the fields like electronic ceramics,super capacitors,gas sensors,solid oxide fuel cells and optical coatings.The binary bismuth oxides are not only an important material used in modern semiconducting devices,but also the basis of the multi-component bismuth oxide research works.The ternary(even more components)bismuth oxides,on the other hand,with the evolution of material science and technology,are attracting more concentrations.For instances,the wide applications in piezoelectric/ferroelectric research and related device manufacturing.As a process based on the chemical surface adsorption of precursors,the atomic layer deposition(ALD)has the characteristics of good consistency of elemental composition,precisely controlled film thickness and superior step coverage of substrate surface,thus gaining a significant position in the ultra-thin film growth.But the ALD cannot precisely control the atomic ratio of Bi-Al-O films like some certain physical(magnetron sputtering,pulsed laser deposition)and chemical methods(sol-gel).Therefore,the study of the relationship between the film chemical composition and the ALD process(and corresponding properties)becomes the prerequisite and basis for the research of the Bi-based multi-component oxide thin films based on the ALD technique.In this paper,the growth of binary and ternary bismuth oxides and related properties were studied systematically,and the following results were obtained:1.The binary non-stoichiometric polycrystalline bismuth oxide(Bi2O3-?)films were successfully fabricated by using triphenyl bismuth(Bi(ph)3)and ozone(03)as the metal and oxygen precursors.The ALD window,saturated pulsed time of Bi(ph)3 and O3 were acquired respectively.A comparatively high film growth rate of 0.23 A/cycle was determined.The properties of films were characterized by using X-ray diffraction(XRD),atomic force microscope(AFM),transmission electron microscope(TEM),UV-visible spectrophotometer,ellipsometer and so on.We discovered that the film grows in the preferred orientation and manifests a mixed mode of layered/island growth,and the related dynamic principle and the forming mechanism were analyzed.With the increase of substrate temperature,the absorption edge of the films appears a red shift,denoting the bandgap of Bi203-?films has a regular one-way trend with the change of substrate temperature2.The two-dimensional Bi2O3-? nanosheets were achieved on the Pt/Si and ITO substrates without masking and catalysts.We analyzed the self-catalyzed effect of the bismuth intermediate products on the formation of ALD-based nanosheets while excluding the catalytic effect of Pt particles on the nanostructure growth.3.We realized the ALD growth of BixAlyO2 composite films by using Bi(thd)3 and TMA as the Bi-source and Al-source precursors respectively.It was found that the Bi content(or A1 content)of the BixAlyOz films does not increase monotonically with the rise of the number of bismuth cycles.As a result,we put forward a growth mechanism based on the diffusion of TMA precursors between Bi2O3 molecules resulted from the steric hindrance effect of Bi(thd)3,and the relevant growth model was established.Moreover,the permittivity of the BixAlyOz films varies correspondingly with the change of bismuth content,thus confirming the parameter of permittivity can be used as a measure of the Bi content in the BixAlyOz composite system.4.The BixAlyOz composite films were prepared by ALD using Bi(ph)3 and TMA as the Bi-source and Al-source precursors,respectively.By replacing the bismuth precursor,it was discovered that the permittivity rises monotonically with the increase in the ratio of the number of bismuth cycles to aluminum cycles,thus verifying that the steric hindrance effect plays a crucial role in the variation of bismuth content of the films(the noticeable/not obvious steric hindrance effect will lead to the non-monotonic/monotonic variation of bismuth content with the increase(or decrease)of the number of bismuth cycles).And the detailed deposition process was also analyzed with the assistance of growth model.Furthermore,the analysis and horizontal comparison of the Bi(ph)3-based BixAlyOz films with the Bi(thd)3-based BixAlyOz films were carried out.