Rene Johannes Marinus van de Veerdonk

Recording potential of bit-patterned media

A comprehensive analysis of the areal density potential of bit-patterned media recording shows that the recording performance is dominated by written-in errors. The statistical fluctuations of the magnetic properties and the locations of the individual bits lead to error probabilities so that some dots are either not recorded at all or cannot be recorded in the time window necessary to ensure synchronized writing. The highest areal densities are obtained with a combination of a pole head, a soft magnetic underlayer, and a storage medium of the composite type. Areal density scenarios of up to 5Tbits∕in.2 are analyzed.

Integration of nanoimprint lithography with block copolymer directed self-assembly for fabrication of a sub-20 nm template for bit-patterned media

We propose a novel strategy to integrate the nanoimprint lithography (NIL) technique with directed self-assembly (DSA) of block copolymer (BCP) for providing a robust, high-yield, and low-defect-density path to sub-20 nm dense patterning. Through this new NIL-DSA method, UV nanoimprint resist is used as the DSA copolymer pre-pattern to expedite the DSA process. This method was successfully used to fabricate a 1.0 Td in(-2) servo-integrated nanoimprint template for bit-patterned media (BPM) application. The fabricated template was used for UV-cure NIL on a 2.5-inch disk. The imprint resist patterns were further transferred into the underlying CoCrPt magnetic layer through a carbon hard mask using ion beam etching. The successful integration of the NIL technique with the DSA process provides us with a new route to BPM nanofabrication, which includes the following three major advantages: (1) a simpler and faster way to implement DSA for high-density BPM patterning; (2) a novel method for fabricating a high-quality dot pattern template through an iterative imprint-DSA-template procedure; and (3) an uncomplicated integration scheme for implementing non-periodic servo features with BCP patterns, thus accelerating the transition of moving the DSA technique from laboratory research to the BPM manufacturing environment.

Quantifiable combinatorial materials science approach applied to perpendicular magnetic recording media

Deposition of films with controlled gradients across the wafer in terms of both composition and thickness were used together with statistical experimental design methodologies to explore large parameter spaces relevant to the optimization of perpendicular magnetic recording media. With this approach, thickness and composition of the media and the interdependencies of these variables were efficiently investigated and correlated to the coercivity of the material and the squareness of the hysteresis loops. To determine dependencies and codependencies between additives to CoCr alloys on the magnetic properties, this method was used to study magnetic layers of CoCrPt, CoCrPtTa, CoCrPtTi, and CoCrTiTa. The best models associated with each alloy had the same terms for the three magnetic parameters measured (Hc, S, and θk,perp). Additions to the CoCr alloy introduced dependencies on the Cr and cross-term dependencies with Cr (i.e., CrTa, CrPt, or CrTi). In some cases, thickness became an important parameter and f...

Scanning Magnetoresistance Microscopy Analysis of Bit Patterned Media Playback

A scanning magnetoresistance microscope (SMRM) was used to enable recording experiments on bit patterned media prototypes not yet suitable for spin-stand evaluation. The SMRM generates a 2D playback response of the media by “dragging” a recording head across the sample using a piezoelectric nanopositioner. A large-scale parameter optimization technique is applied to extract relevant parameters such as pulse amplitude, pulse width, and pulse position from the 2D playback response. The parameters were analyzed to learn that the pulse response of our recording head cannot be accurately modeled as a Gaussian function. The error in the optimized parameters is dominated by intertrack interference and to a lesser extent measurement resolution and thermal drift.

Method for seed and underlayer optimization of perpendicular magnetic recording media

A set of seed and underlayers for thin film perpendicular recording media has been optimized using a technique involving simultaneous thickness and composition gradients on a single test wafer. Magnetron sputtering under ultrahigh vacuum conditions in Ar gas was used for the deposition of the layers. The structure being optimized consisted of a Ta seed layer, RuxCo1−x, Co63Cr37 underlayers, and a Co68Cr18Pt8B6 hard magnetic layer. One of the layers in the stack on a wafer has been deposited so that both a thickness variation and composition variation occurred. The method allows cross terms between thickness and the individual compositional terms to be investigated. Coercivity and squareness of the samples was measured by magneto-optical Kerr rotation. The results showed that for the range of thickness under investigation, the highest coercivity and squareness does not occur for the same set of conditions. Maximum squareness is reached without a radio frequency (rf) bias, while the coercivity increases fur...