Fabrication and characterization of bit patterned media at 1.5 Tdots/in2 and beyond

Continuing areal-density growth is critical for the hard disk drive industry to meet the increasing demand in data storage, and to improve costs. Heat-assisted magnetic recording (HAMR) is expected to be introduced in products as perpendicular magnetic recording (PMR) approaches its limitations in areal density growth. Beyond this, bit patterned media (BPM) recording is considered to provide a path for areal density growth above the limits imposed by granularity in PMR and HAMR media. In BPM, one bit of information is stored in a lithographically defined dot with typical dimension in the order of a few nanometers. Thus, BPM presents extreme challenges to lithography because of the small feature size required for high areal density. Moreover, very tight dot size and spacing tolerance control, and incorporation of servo features are critical to facilitate recording with a transducer. BPM fabrication starts with patterning of the dots in quartz wafers to form templates for nano-imprint lithography (NIL). At Seagate, patterning of such templates by directed self-assembly (DSA) of block copolymers has been demonstrated as a viable lithography approach for areal density up to 5 Tdpsi. A mix-and-match DSA and conventional lithography scheme has been successfully developed for fabricating imprint templates, each comprising regular arrays of dots in data sectors, and non-periodic dot patterns in servo sectors. Templates with fully integrated servo patterns and with areal density of up to 2 Tdpsi (Figure 1) have been fabricated. Subsequent media fabrication involves transferring the BPM features from a template into magnetic thin films by NIL and ion-beam etching. Using this approach, BPM media with fully functional integrated servo features has been successfully fabricated on 2.5” disks with areal density of up to 1.5 Tdpsi. On spin-stand, BER of 3.7 × 10
⁻³
has been measured on 1 Tdpsi BPM disks, whilst the best write error rate recorded at 1.5 Tdpsi BPM currently stands at 2.5×10
⁻²
(Figure 2). Although significant milestones have been achieved in BPM technology, many challenges still remain, principally in recording margin, patterning to meet skew requirement, density extensibility, dot morphology control, and magnetic material limitations. Possible solutions such as patterned rectangular bits with lamellae-forming BCP and double patterning process, and heated dot magnetic recording (HDMR) will be discussed. At system level, integration challenges from drive architecture perspective will also be addressed.