First-principles Study Of Magnetic Properties And Work Function Of Fe_1-xY_x/Fe（001）（Y=Mn,Gd）

The market’s need for higher integrated performance and circuit density has forced the gate dielectric layer thickness to decrease rapidly. Due to the rapid increase in tunneling current, the use of conventional SiO2films as gate oxide is reaching its limit. As possible replacements for SiO2, various alternative high-k materials have being investigated. But at the same time, a high value of threshold voltages can be caused by Fermi level pinning occured at the poly silicon/high-k dielectric interface. Moreover, the depletion layer formed in poly silicon gates leads to decreased effective gate capacitance. Fortunately, we can avoid those problems by introducing metal gates.Therefore, with the develop of micro-electronics, the research and application of MOSFET with metal gate/high-k dielectric structure becomes a consequentially trend. In this dissertation, we study the effects of surface alloying, spin polarization, surface adsorption on the magnetism and work function of metal gates using first-principles methods. This dissertation is divided into five parts:Firstly, the research background were introduced, including the necessary and difficulty of MOSFET with metal gate/high-k dielectric structure, the primary means to tuning the work function of metal gate at this stage. Additionally, we also present the details to the theoretical basis of first-principles calculation and the software of VASP involved in this dissertation.Secondly, we have studied the influence of the spin polarization, spin arrangement and surface alloying on the magnetic properties and work function of Fe (001) and Fe1-xMnx/Fe (001) using first-principles. The calculated results reveal that the spin arrangement and alloying have evident effect on the work function and moment of Fe1-xMnx/Fe (001). We find that the work function is not only determined by the charge transfer but also by the spin polarization. For NM case, the work function of Fe1-xMnx/Fe (001) system is sensitive to the Mn doping content. However, when considering the spin polarization, the Mn doping seems not evidently affect the work function.Thirdly, Work functions and magnetic moments of C adsorbed Mn/Fe(001) surfaces with different C coverages θ and magnetic alignments between Cr and Fe atom moments are investigated using first-principles methods. he calculated results reveal that the spin arrangement has evident effect on the work function and magnetism of surface systems.We also found that the carbon adsorption could greatly affect the work function of all systems with different staes.Next, The magnetism and workfunction of Fe1-xGdx/Fe (001) films are investigated using first-principles methods. The calculated results reveal that Fe(001) doped with Gd on the surface would greatly affect the geometrical structure of the system., which leads to the change of magnetic coupling between Gd and Fe atoms. It can be also found that the surface atoms average magnetic moment, Fermi energy (EF) and workfuction change along with the value of x regularly. On the basis of analysis and discussion, we concluded that the changes of the work functions and magnetic moments are mainly determined by Fermi level, the electron transfer and the surface structure.Finally, a conclusion for this thesis is given.