nanostructures design and fabrication for magnetic storage applications

Abstract

As technology scales down, many opportunities are available for conventional magnetic storage devices. The advent of nanofabrication technology offers capabilities in patterning materials and modifying the magnetic properties. The focus of this research is to design and fabricate magnetic nanostructures and understand the magnetic behavior modified by nanostructures, to generate new devices for magnetic storage applications. This dissertation has concentrated on the fabrication, simulation and characterization of magnetic nanostructures for new storage applications. First, novel techniques have been successfully developed to fabricate nanostructures with different shapes and dimensions below the resolution limit of photolithography tool. Anisotropic nanostructures, diamonds and triangles, have been obtained by over-exposure technique; nano-rings, both centered and de-centered, have been obtained by lateral etch technique and ALD spacer mask technique. All these techniques are simple and use conventional photolithography. Large area, high density nanostructures have been obtained at low cost. The above techniques have been investigated and optimized for better control of magnetic properties. Second, anisotropic nanostructures have been characterized correlated with simulation to understand the shape anisotropy effect on magnetic behavior. Coercivity change and angular dependent behavior result from pinning the magnet by the nanostructures and these have been explored. Dimensions of nanostructure also play an important role in changing the magnetic properties. At constant density, nanostructures of larger size introduce more anisotropy and result in higher coercivity and remanence. Third, nano-rings have been characterized correlated with simulation to study the magnetic state switching process. Various dimensions of rings have been compared and have revealed that the vortex state in rings is affected by the dimensions of inner diameter, width and thickness. The shape anisotropy and magnetostatic energy play an important role in vortex state formation and maintenance. The interaction effect in ring array has also been explored for high density MRAM design application. Fourth, feasible design and fabrication of de-centered rings have been developed for vortex chirality control. The process is simple and the shift of the inner circle can be easily adjusted. The asymmetry in the de-centered rings controls the movement direction of the domain walls, leading to predictable vortex chirality. Finally, future research on the application of the nanostructure on the magnetic storage devices is presented. The etching of magnetic materials needs to be further optimized for nanostructure geometries control. Ring-shaped magnetic tunneling junction (MTJ) needs to be fabricated and characterized especially using spin-torque-transfer technique to investigate the advantages of rings. Other applications of nano-rings can be further explored.