Bit-Patterned Magnetic Recording: Theory, Media Fabrication, and Recording Performance

Abstract

Bit Patterned Media (BPM) for magnetic recording provides a route to thermally stable data recording at >1 Tb/in 2 and circumvents many of the challenges associated with extending conventional granular media technology. Instead of recording a bit on an ensemble of random grains, BPM is comprised of a well ordered array of lithographically patterned isolated magnetic islands, each of which stores one bit. Fabrication of BPM is viewed as the greatest challenge for its commercialization. In this article we describe a BPM fabrication method which combines rotary-stage e-beam lithography, directed self-assembly of block copolymers, self-aligned double patterning, nanoimprint lithography, and ion milling to generate BPM based on CoCrPt alloy materials at densities up to 1.6 Td/in 2 (teradot/inch 2 ). This combination of novel fabrication technologies achieves feature sizes of <10 nm, which is significantly smaller than what conventional nanofabrication methods used in semiconductor manufacturing can achieve. In contrast to earlier work which used hexagonal closepacked arrays of round islands, our latest approach creates BPM with rectangular bitcells, which are advantageous for integration of BPM with existing hard disk drive technology. The advantages of rectangular bits are analyzed from a theoretical and modeling point of view, and system integration requirements such as provision of servo patterns, implementation of write synchronization, and providing for a stable head-disk interface are addressed in the context of experimental results. Optimization of magnetic alloy materials for thermal stability, writeability, and tight switching field distribution is discussed, and a new method for growing BPM islands from a specially patterned underlayer -referred to as "templated growth" -is presented. New recording results at 1.6 Td/in 2 (roughly equivalent to 1.3 Tb/in 2 ) demonstrate a raw error rate <10 -2 , which is consistent with the recording system requirements of modern hard drives. Extendibility of BPM to higher densities, and its eventual combination with energy assisted recording are explored.Index Terms-Bit patterned media, hard disk drive, block copolymer, self-assembly, double patterning, e-beam lithography, sequential infiltration synthesis, nanoimprint lithography, templated growth, thermal annealing, Co alloys, magnetic multilayers, interface anisotropy, magnetic recording, write synchronization, prepatterned servo, areal density.

Fabrication of bit patterned media using templated two-phase growth

“…5 A similar long-range ordered nanostructure was also reported by Albrecht et al, using the template growth paradigm. 6 The previously explored approaches for BPM fabrication 7 subtractive or additive. In the case of the subtractive ("top-down") approach, 8,9 the magnetic media film is first deposited as a sheet film and subsequently patterned into pillars using ion-milling or methanol etching, using etch masks defined using e-beam, 10 nanoparticle 11 or nanoimprint lithography, directed block copolymer self-assembly, [12][13][14] or combinations of these.…”

Writing Field Analysis for Shingled Bit-Patterned Magnetic Recording

“…The main effect and two-interaction effect of the design parameters can be evaluated based on the responses of factorial runs (1)(2)(3)(4)(5)(6)(7)(8), and the quadratic effect can be evaluated based on the axial and center runs (9)(10)(11)(12)(13)(14)(15). Strength of each effect can be indicated by the percentagewise absolute value of the coefficient in RSM model, as shown in Figure 4.…”

“…In recent years, several new methods and techniques have been proposed to manage this problem, such as heat-assisted magnetic recording (HAMR) [2], microwave-assisted magnetic recording (MAMR) [3,4], shingled magnetic recording (SMR) [5,6], and bit-patterned media recording (BPM) [7,8]. In the BPM scheme, the data are stored in patterned magnetic islands instead of grain clusters in conventional continuous media to achieve higher SNR and thermal stability.…”

Patterning of L10FePt nanoparticles with ultra-high coercivity for bit-patterned media

“…Bit-patterned media (BPM) system, in which a single magnetic bit is recorded on a pre-defined single magnetic dot, has the higher SNR due to the absence of transition noise and erase bands, and it has emerged as a promising technology for extending magnetic data storage density beyond 1 Tb/in 2 . 2 As reported in the Advanced Storage Technology Consortium, the novel storage architecture by combining BPM and Heat-Assisted Magnetic Recording (HAMR) will lead to 10-terabit-per-square-inch (Tbpsi) areal density by 2025. Furthermore, as demonstrated by Hitachi Global Storage Technologies (HGST), BPM will be improved towards higher areal density by utilizing nanolithography to break magnetic media down into small regions or bit "islands" on a platter's surface.…”