Heat-assisted magnetic recording media materials
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ssisted magnetic recording media materials
lithographically defined magnetic bits,29 may provide a path for recording media beyond ∼4 Tbpsi. HDMR relaxes some of the magnetic layer material requirements, but adds substantially new materials and processes to form bits comprising high Ku magnetic islands. HDMR media fabrication typically starts with a continuous FePtX film, where X is a nonmagnetic segregant, and uses advanced lithography, including e-beam, nanoimprint, and directed self-assembly (DSA) to define the magnetic islands. HDMR presents extreme lithographic challenges to achieve feature sizes well below Figure 3. (a–b) Plan-view and cross-sectional transmission electron microscope bright-field 10 nm. Moreover, successful recording requires images of FePt-30.6 vol% C films deposited by the compositionally graded process to the nominal thickness of 12 nm. The grain aspect ratio is near 2.0. (c) High-angle annular darktight control of dot size, shape, and spacing, in field image showing a well-ordered L10 structure except near the surface. (d) Magnetization addition to the incorporation of servo features to curves show perpendicular magnetic anisotropy film with substantial in-plane component. aid the head–media alignment. Seagate has sucNote: OP, out-of-plane; IP, in-plane. cessfully fabricated 5 Tbpsi FePt-based media30 and demonstrated track-following with readwrite capability of 1.5 Tbpsi HDMR.31 distributions, anisotropy distributions, and thermal capacity variations in the grains.5,25,26 Chernishov et al. provide measurements that clearly indicate that σ TC is a strong function of grain volume.26 To reach HAMR’s full potential, it is critical to fabricate FePt-C media with fully ordered 4–5 nm grains, high anisotropy (μ0Hk > 9 T) and narrow Curie temperature distributions (1.2 necessarily implies that the down-track (radial) full pitch be smaller than 22 nm. Unfortunately, 22-nm pitch seems to be near the limit at
Figure 5. (a) Fabrication of submaster templates from e-beam and block copolymer lithography. One template contains circumferential track lines (left), while the second template includes zoned and skewed radial lines (right). After double imprint on a master template, the two patterns intersect forming rectangular islands. Circumferential lines—top-down scanning electron microscope (SEM) images of (b) e-beam resist pattern with a full pitch, LS = 49 nm; (c) guided PS-b-PMMA pattern with a period, L0 = 24.5 nm; (d) Si lines after pattern transfer. Radial lines—top-down SEM images of (f) e-beam resist pattern with LS = 58 nm; (g) alumina lines formed through sequential infiltration synthesis on guided PS-b-PMMA lamellae with L0 = 29 nm; (h) TiO2 spacer lines with full pitch of 14.5 nm formed through selfaligned double patterning. (e, i) Cross-sectional SEM images of a sister sample as shown in (d, h). (j, k) Top-down SEM images of magnetic dots with areal density of 1.4 and 1.6 Tbpsi. Scale bars = 100 nm.33,34
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