M. Farhoud

Fabrication of patterned media for high density magnetic storage

Arrays of discrete, lithographically patterned magnetic elements have been proposed as a new generation of ultrahigh density patterned magnetic storage media. Interferometric lithography has been used to make prototype arrays over large areas with periods of 100–200 nm. Arrays of magnetic pillars, pyramids, and dots have been made by electrodeposition, evaporation and liftoff, and etching processes, and the magnetic properties of the particles and their mutual interactions have been measured.

Magnetic behavior of lithographically patterned particle arrays (invited)

This article reviews recent progress in the fabrication, characterization, and analysis of large area arrays of sub-100-nm magnetic particles made by lithographic techniques. Particles are made by electrodeposition, evaporation and liftoff, or sputtering and etching, leading to a wide range of shapes, compositions, and microstructures. The remanent states, magnetic hysteresis, and uniformity of the particles and the interparticle interactions will be discussed.

Micromagnetic behavior of conical ferromagnetic particles

Large area arrays of cobalt and nickel particles with truncated conical shapes and diameters of 80–120 nm have been prepared using interference lithography combined with an evaporation and lift-off process. The magnetic hysteresis has been measured and the remanent states of the particles have been compared with a three-dimensional micromagnetic model. The model shows a transition from “flower” to “vortex” magnetization states as the particle size increases. The distribution of switching fields and the magnetostatic interactions between particles have been characterized. Both lead to a slow approach to saturation in the hysteresis loops. The suitability of such arrays for data storage is discussed.

Fabrication of 200 nm period nanomagnet arrays using interference lithography and a negative resist

Magnetic information storage density has increased at the rate of 60% per year for the past seven years. There is wide agreement that continuation of this trend beyond the physical limits of the continuous thin-film media currently used will likely require a transition to discrete, lithographically defined magnetic pillars. Interference lithography (IL) appears to be the most cost-effective means of producing two-dimensional arrays of such pillars. IL can rapidly expose large areas with relatively simple equipment, without the need for a mask, and with fine control of the ratio of pillar diameter to period. We show that negative-tone imaging yields three times the contrast of positive-tone imaging for the generation of holes in photoresist, suitable for subsequent deposition or electroplating of magnetic material. We use a negative i-line, chemically-amplified resist (OHKA THMR-iN PS1) to form 200 nm period arrays of magnetic dots in Co and Ni. Such arrays, with a variety of well controlled diameters, are...

In-plane anisotropy in arrays of magnetic ellipses

Large area samples of submicron arrays of elliptical thin Co dots were fabricated using interference lithography and ion milling. The magnetic properties were investigated by MFM and hysteresis loops were measured at different temperatures. The temperature dependence of coercivity was measured suggests that the thermal fluctuation plays an important role in the magnetization reversal mechanism.

The effect of aspect ratio on the magnetic anisotropy of particle arrays

Arrays of evaporated nickel particles with a variety of diameters (75–122 nm) and aspect ratios are fabricated in order to study the effect of the particles’ geometry on their magnetic behavior, interactions and switching mechanism. Hysteresis loops generated by simulating single-domain particles with out-of-plane magnetization are compared to the experimentally obtained data.

In-plane magnetic anisotropy in CoCrPt and CoCrTa films deposited onto patterned silicon substrates

Topographically induced in-plane magnetic anisotropy has been observed in CoCrTa and CoCrPt films deposited onto oxidized silicon substrates which are lithographically patterned with fine grooves of period 200–320 nm and amplitude 20–50 nm. The coercivity and remanence are higher parallel to the grooves. Anisotropy has been observed in both rf- and dc-magnetron sputtered films with a (1120) preferred orientation, which is achieved by growth at elevated temperature on a (200)-oriented Cr underlayer at low base pressures. Anisotropy increases with the amplitude of the grooves in the silica substrate.

Extending Spatial-Phase-Locked Electron-Beam Lithography to Two Dimensions

The global-fiducial grid mode of spatial-phase-locked electron-beam lithography in two dimensions is investigated. A phase-locking scheme for two-dimensions is proposed and analyzed. An expression for the minimum locking dose is derived. The use of a scintillating grid is proposed, and results from optical detection of a scintillating fiducial grating are reported.