Preparation And Properties Of Bismuth Titanate Low-dimensional Materials

With the quick development of microelectronics, the size of semiconductor devices is becoming smaller and smaller. SiO₂, as the present gate dielectric, can't satisfy this trend in the coming several years. Thus, the research of high-k gate dielectric materials will become a focus in the field of present microelectronic materials. In the numberous selected materials, Bi₂Ti₂O₇ as one of the hopeful high-k gate dielectric materials substituting to SiO₂ has been identified as a promising candicate, which belongs to the bismuth titanate.In present, the phase of Bi₂Ti₂O₇ in the bismuth titanate series has been studied a few. However, polycrystalline thin films of this composition have high permittivity and low leakage current density, which have a widely foreground. High permittivity dielectrics are widely investigated as alternative gate insulating layers in advanced MOS (metal-oxide-semiconductor) transistors. It also has been used as a buffer layer to improve the electrical properties of ferroelectric PZT thin films. However, Bi2_Ti₂O₇ can easily transformed into Bi₄Ti₃O₁₂ at high temperature. The chemical stability would be heightened after substituting Bi ions with some other ions during the preparation of ceramics, as the same as La-modified Bi₂Ti₂O₇ thin films. In order to make the best use of our abundant rare earths, we expect improve its stability and obtain better properties by modifying other lanthanides.In this paper, we prepared the Sm-modified Bi₂Ti₂O₇ precursor solutions by metalorganic solution deposition method and by spin-coating in different substrates. The main contents are as following:In the third chapter, above all, we prepared Sm-doped (Bi_1-xSm_x)₂Ti₂O₇ thin films by CSD. It has been found that the crystalline temperature, surface micrograph and electrical properties of thin films have been influenced with different Sm content. Thinking about these factors, we think that the film of x=0.1 has preferable property. Then, we studied the influence of precursor solution's concentration on thin films under the condition of the same Sm content. We found that the influence of precursor solution's concentration on the thin film's electrical property is more complex. According to these factors, we think the optimized composition of thin films is the precursor solution's concentration is 0.1, the Sm ion of thin films is x=0.1.In the fourth chapter, we studied deeply about (Bi_0.9Sm_0.1)₂Ti₂O₇(BSTO(0.1)) films deposited on p-Si and Pt substrates, respectively. The BSTO(0.1) films annealed at 600℃ for 10min have better polycrystalline and crystallize. What is more, BSTO(0.1) has a higher annealing temperature than Bi₂Ti₂O₇ and is much better stability than La-doped films. The reason we think is not only the charge compensation, but also the Sm ion's radius is nearer Bi ion's than La ion's (Bi³⁺(0.93A)3+( 1.00A)3+( 1.14A)) . The AFM image shows the surface is homogeneous with spherical grains. Cross sectional micrographs of BSTO(0.1) thin films on Si substrate shows that the interface is very clarity and there is no interfacial diffuse. The thickness of films is about 490nm. The films on Si substrate annealed in different conditions exhibit complex electrical properties. The better electrical property is showed on Pt substrate.Besides, we studied the powder of Bi₂Ti₂O₇, there are some differences in the crystalline at the same composition. The TEM shows the better surface and sharp. The much more complex electrical properties are studied.