| The purpose of this dissertation is to investigate the magnetization configuration and switching behavior of sub-micron patterned elements for magnetic random access memory (MRAM) applications. The investigated shapes include rings and "Pac-man" (PM) shaped elements. The PM element is a newly designed shape proposed in this dissertation. In Chapter 1, currently emerging non-volatile memories are reviewed, which include flash memory, ferroelectric random access memory (FRAM), ovonic unified memory (OUM), and MRAM. In particular, MRAM memory is emphasized, and the goals of this dissertation related with MRAM are introduced. In order to fabricate patterned magnetic elements, DC and RF sputtering deposition, electron-beam lithography with lift-off or ion milling processes were used. Magnetization configuration and switching behavior of patterned magnetic elements were characterized by a magnetic force microscope, vibration sample magnetometer, BH loop tracer, and magneto-optic Kerr effect system. Micromagnetic simulation was also performed to study the switching mechanism and energy contribution on their reversal process. Detailed fabrication steps and measurement tools are presented in Chapter 2. In Chapter 3, magnetization modes are classified and reviewed depending on element shape applied to MRAM. In this chapter, current challenges of linear and circular magnetic elements are discussed. In Chapter 4, the geometry dependence of magnetization configuration, switching field distribution, selectivity, and magnetic switching behavior of PM elements are reported. The geometry includes the slot angle, thickness, elements size, shape anisotropy, and slot line. Finally, the most appropriate element showing a well-defined single domain at remanent state, for a low switching field distribution, for high selectivity, and for coherent magnetic switching are explored for its MRAM application. In Chapter 5, the magnetic properties and head-to-head (HTH) domain wall of patterned permalloy ring elements are investigated depending on ratios of inner to outer diameter, ring size, and thickness. The HTH domain wall formation process of macroscopic ring elements with vortex HTH domain walls are also discussed. In Appendix A, six articles related with Pac-man elements are reprinted as references. In addition, in Appendix B, magnetic switching properties and domain wall configurations of continuous ferromagnetic bilayer films are reprinted as background research of magnetism. |
