氧空位缺陷对PbTiO_3铁电薄膜漏电流的调控

基于非平衡格林函数及密度泛函理论第一性原理计算方法,计算了Fe, Al, V和Cu四种阳离子掺杂对氧空位缺陷引起的PbTiO_3铁电薄膜漏电流的调控.研究表明:Fe和Al离子掺杂将会增大由其中氧空位缺陷导致的铁电薄膜的漏电流,而Cu和V离子掺杂对该漏电流的大小具有明显抑制作用.这是因为Cu和V掺杂对氧空位缺陷有明显的钉扎作用.相比于半径更大的Cu离子,由于V的离子半径更小,且更接近于PbTiO_3铁电薄膜中Ti的离子半径,可以预言V离子更可能被掺杂进入薄膜,从而抑制氧空位缺陷引起的漏电流.研究结果对铁电薄膜器件的电学性能控制和优化有一定的理论指导意义.

Effect of oxygen vacancy defect on leakage current of PbTiO3 ferroelectric thin film

Ferroelectric (FE) materials have been extensively applied to the multifunctional electronic devices, particularly the FE memories due to their excellent physical properties. The FE memory is a kind of nonvolatile memory device, and it could overcome the shortcomings of the traditional memory. But the development of the FE memory is very slow due to the FE failure problem. However, with the continuous decrease of the thickness of FE thin film, when it reaches microns or nanometers in magnitude, the leakage current is the main cause of the FE failure of FE thin film. The leakage current of FE thin film is directly related to whether the FE memory is applicable, and it has been the hot spot of scientific researches. There are still a lot of factors influencing the FE memory leakage current except for the thickness of the film, such as interface, processing temperature, defect, domain wall, etc. Of these factors, the defect and domain wall are the most common and the most probable. In this paper, the first-principle calculation method through combining the density function theory with the nonequilibrium Green's function is used to systematically study the influence of oxygen vacancy defect on the leakage current of the FE thin film. The doping with four kinds of Cu, Al, V, and Fe cations is used to regulate and control the leakage current of the FE thin PbTiO₃ film caused by the oxygen vacancy defects. We investigate the leakage current induced by oxygen vacancies in PbTiO₃ films, and the doped PbTiO₃ thin FE films having oxygen vacancies. It is found that Fe and Al doping will increase the leakage current of oxygen vacancy defects of FE thin films, while the Cu and V doping significantly reduce the leakage current of oxygen vacancy defects of FE thin films. This is because the Cu and V doping have obvious pinning effect on oxygen vacancy defect. In addition, we find that the oxygen vacancies are pinned by Cu and V atoms due to the fact that the formation energy of oxygen vacancies can be remarkably reduced. So Cu and V doping in PbTiO₃ not only induce the leakage current but also improve the fatigue resistance of the FE thin film induced by oxygen vacancies. Moreover, since the ionic radius of V is closer to the ionic radius of Ti than the ionic radius of Cu, V is easier to implement doping to suppress the leakage current caused by the oxygen vacancy defects. These conclusions are of important theoretical significance and application value for improving the performance of FE thin films and their FE memories.