Characterisation of micron sized ferromagnetic structures fabricated by focussed ion beam and electron beam lithography

• Main Author: O'Neill, Robin W.
• Published: University of Glasgow 2007
• Subjects: 621.381531; QC Physics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.443420

Traditionally electron beam lithography (EBL) has been used to fabricate micron and sub-micron sized devices, such as Γ and Τ gates for metal-semiconductor devices for study within the semiconductor industry. EBL is also used for the fabrication of ferromagnetic elements for use as components in magnetic random access memory (MRAM) and read/write heads in hard disk drives (HDD). MRAM is being investigated as a direct replacement to standard semiconductor RAM as it has lower power consumption and is a non-volatile memory solution, although the areal density, at present, is not as great. Smaller read/write heads are necessary for HDD as recent advances now allow for perpendicular magnetisation (as opposed to parallel magnetisation) of films and increase the areal density to 100 Gb/inch2, four times the current value. In this thesis, the physical and magnetic properties of such micron-sized devices that have been fabricated by focussed ion beam (FIB) lithography for comparison to those fabricated by the EBL method are discussed. In addition to this work, the physical and magnetic properties of micron-sized element that have been irradiated using the 30 keV gallium ion source are also discussed. Also in this thesis, the results of 10×10 μm2 arrays of 50 nm thick polycrystalline cobalt elements (270×270 nm2 with a 400 nm period) that are fabricated by EBL to determine if there is any magnetic superdomain structure present are discussed. Bright field imaging in a transmission electron microscope (TEM) is used to investigate the physical structure of the ferromagnets, such as the grain size, element roughness and dimensions. Additional information about the topography is measured by atomic force microscopy (AFM). The magnetic properties, such as the magnitude of the applied field at which irreversible events happen and the domain structure, are investigated by the Fresnel imaging and the differential phase contrast modes of Lorentz microscopy. A programme known as object orientated micromagnetic framework (OOMMF) is used to model the magnetic properties of such structures.