Titanate Salts Preparation And Properties Of Ferroelectric Thin Films

In resent twenty or thirty years, people aim at developing ferroelectric memories, such as ferroelectric random access memory, ferroelectric field effect transistor. They have intensively studied ferroelectric thin films integrated with semiconductors. As the widely used ferroelectric materials, such as PbTiO₃, Pb(Zr,Ti)O₃, Pb(Mg,Nb)O₃, etc contain PbO from 60% to 70% by weight, which are opposite to the needs of environmental protection. Moreover, Pb(Zr,Ti)O₃ films, sandwiched in metal electrodes, may suffer from severe polarization fatigue, reduction of remanent polarization due to repetitive switching. Although using metal oxide electrodes can solve the fatigue problem, it is not easy to synthesize and the leakage current can increase. SrBi₂Ta₂O₉ films have been found to show a fatigue-free characteristic with simple metal electrodes, and attracted much attention in ferroelectric memory materials. But its annealing temperature is higher and it has lower remanent polarization. In order to eliminate these two problems, people have attempted to use modified annealing method, buffer layer and element-substituted. Bi₄Ti₃O₁₂ films show a degradation property after being subjected to ～10⁸ read/write switching cycles. Since 1999, lanthanide-substituted Bi₄Ti₃O₁₂ thin films have been studied.Recently, Na_0.5Bi_0.5TiO₃, K_0.=5Bi_0.5TiO₃ as lead-free materials, have attracted considerable attention from the viewpoint of environmental protection. Both of them belong to ABO₃ perovskites with two different ions such as Na⁺, Bi³⁺ or K⁺, Bi³⁺ at the A site, Ti⁴⁺ at the B site. Several previous studies are focused on the properties of Na_0.5Bi_0.5TiO₃ ceramic or crystal, such as piezoelectric, ferroelectric, pyroelectric properties and optics properties. K_0.5Bi_0.5TiO₃ has rarely been reported because it is difficult to make ceramic or crystal. The studies about Na_0.5Bi_0.5TiO₃ and K_0.5Bi_0.5TiO₃ films are lacking.It is necessary to explore the novel kinds of ferroelectric films or find ways to make the present film materials show good properties. In this work, we prepared Na_0.5Bi_0.5TiO₃-K_0.5Bi_0.5TiO₃ system and lanthanide (Nd, Sm, Pr)-substituted Bi₄Ti₃O₁₂ thin films and studied their properties.A manufacturing processing for producing ferroelectric films and their integrated device at least include the following characteristics: â‘ Applicability of the processes to deposition of ferroelectric films and integration with metallic or conductive oxide electrode layers. â‘¡ Compatibility with integrated device...