High-Throughput Top-Down Fabrication of Uniform Magnetic Particles

Ion Beam Aperture Array Lithography was applied to top-down fabrication of large dense (108–109 particles/cm2) arrays of uniform micron-scale particles at rates hundreds of times faster than electron beam lithography. In this process, a large array of helium ion beamlets is formed when a stencil mask containing an array of circular openings is illuminated by a broad beam of energetic (5–8 keV) ions, and is used to write arrays of specific repetitive patterns. A commercial 5-micrometer metal mesh was used as a stencil mask; the mesh size was adjusted by shrinking the stencil openings using conformal sputter-deposition of copper. Thermal evaporation from multiple sources was utilized to form magnetic particles of varied size and thickness, including alternating layers of gold and permalloy. Evaporation of permalloy layers in the presence of a magnetic field allowed creation of particles with uniform magnetic properties and pre-determined magnetization direction. The magnetic properties of the resulting particles were characterized by Vibrating Sample Magnetometry. Since the orientation of the particles on the substrate before release into suspension is known, the orientation-dependent magnetic properties of the particles could be determined

The Effect of Size Distribution on the Switching Field Distribution of Co/Pd Multilayered Nanostructure Arrays

We use Ion Beam Proximity Lithography (IBPL) to produce 4 mm times 4 mm arrays of 220 nm dots in perpendicularly - oriented Co/Pd multilayered media. IBPL is used to reduce the size distribution sigma D of the arrays, and subsequently He + ion irradiation is used to reduce their anisotropy. The switching field distribution sigma Hcr /H Cr is measured for each sample before and after irradiation, and a linear relationship is experimentally found between sigma Hcr /H Cr and sigma D . We argue that the slope of the line is due to the self-demagnetization effect of individual dots (and therefore, it is not strictly a line) and that the intercept of the line is inversely proportional to the permeability of the nanostructured material

The effects of edge defects on the switching characteristics of bit patterned media

We present the results of micromagnetic studies on realistic patterning defects in perpendicularly oriented magnetic thin films. Both undercut and line edge roughness are investigated systematically with simulations using simple test structures to see the effect of the side wall angle, the roughness amplitude on a nanostructureiquests switching field, and the roughness period on mathematically tractable figures. We then run simulations of hysteresis loops of actual 200 nm diameter nanostructures using AFM images to define the structure boundary and compare the results to MFM images of DC demagnetized dots

Graded bit patterned magnetic arrays fabricated via angled low-energy He ion irradiation

A bit patterned magnetic array based on Co/Pd magnetic multilayers with a binary perpendicular magnetic anisotropy distribution was fabricated. The binary anisotropy distribution was attained through angled helium ion irradiation of a bit edge using hydrogen silsesquioxane (HSQ) resist as an ion stopping layer to protect the rest of the bit. The viability of this technique was explored numerically and evaluated through magnetic measurements of the prepared bit patterned magnetic array. The resulting graded bit patterned magnetic array showed a 35% reduction in coercivity and a 9% narrowing of the standard deviation of the switching field

Magnetic Annular Nanostructure Fabrication Using Ion Beam Proximity Lithography

We describe the fabrication of large-area magnetic ring structures using ion beam proximity lithography (IBPL) to pattern an array of circular openings and then use a conforming oxide coating to define the ring structure through the sidewall coating. Arrays of Permalloy rings with sub 500 nm outer diameter and 150 nm inner diameter on a 650 nm pitch over a 5.5 mm times 6 mm area were fabricated to study transitions between the micromagnetic configurations within these structures. The results suggest that the field required for onion-to-vortex transition and field required for vortex-to-onion transition to be 0Oe and 400Oe, respectively

Fabrication of patterned recording medium using ion beam proximity lithography

We describe the lithographic structuring of large-area patterned medium samples with sub-50 nm features using ion beam proximity lithography (IBPL). The quality of the patterns formed in IBPL system is primarily limited by the quality of the stencil masks. Hence, the emphasis of this work has been to develop a reliable mask fabrication process that can achieve a size uniformity that is suitable for patterned media. We have developed a mask fabrication approach that incorporates palladium as a hard mask for transferring the lithography pattern through a silicon nitride membrane. A conformal gold coating allows for further reduction of the mask features without a significant increase in the feature size variation. An average standard deviation of 3 nm and 5 nm was measured during various steps of the stencil mask fabrication and after printing using IBPL in PMMA resist, respectively. Patterned medium prototypes with features ranging from 40 nm to 300 nm have been fabricated and magnetic properties measured. A 6-12 fold increase in coercivity was measured for multilayer samples after patterning. Ion irradiation of patterned multilayer samples was also studied as a means to control magnetic anisotropy as well as to evaluate possible ion irradiation damage involved in ion-beam proximity lithography patterning. Patterned multilayer samples show a decrease in coercivity from 11 kOe for as-patterned to 0.3 kOe for 800 muC/cm 2 and suggests that ion irradiation can be an integral part of bit patterned medium fabrication for anisotropy control

Nanoscale bit-patterned media for next generation magnetic data storage applications

Design considerations and fabrication of bit-patterned magnetic recording media are presented. The application of ion-beam proximity printing, a high-throughput direct-write lithography, to media patterning is evaluated. Ultra-high magnetic anisotropy (Co/Pd)N magnetic multilayers are analyzed as candidates for patterned recording layers. Following patterning, optimized multilayers are shown to exhibit coercivity values well in excess of 14kOe. It is found that the magnetization reversal in patterned bits takes place via domain wall nucleation and propagation. The nucleation field and the location of the nucleation site strongly depend on the bit edge imperfections and contribute to finite switching field distribution. Playback off a bit-patterned media using various magnetic reader designs is analyzed using reciprocity theory