Nano-fabrication of Magnetic Recording Media

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Nano-fabrication of Magnetic Recording Media

• Wesley Tennyson
• Engineering Physics Ph.D. Candidate
• Homer L. Dodge Dept. of Physics and Astronomy
• at
• The University of Oklahoma

Presented forFundamentals of Nanotechnology
From Synthesis to Self-Assembly
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Outline

• Motivation
• Nano-Fabrication Essentials
• High density dots are not enough
• Current Technology
• Perpendicular media
• Patterned Creation
• Lithography
• Guided self-assembly
• Imprint lithography
• Langmuir-Blodgett
• Aperture array lithography
• Summary

areal density bit density x track density
J. Phys. D Appl. Phys. 35 (2002) R157-R161.
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Motivation

• 40 growth rate of areal density
• ? 700 Gbits / in2 by 2011
• Superparamagnetic Effect limits continued
  reduction of grain size below d 20nm.
• Patterned nanoparticles or patterned media (PM)
  avoids this problem.
• PM can have higher
• track and linear densities.
• Nanoparticles typically
• have only one magnetic domain
• ? better signal to noise
• With patterned media 1 Tbit/in2 may be achieved.

(Left) AFM image of a typical Fe dot array
fabricated using alumina mask anodized at 40 V.
The standard deviation of the dot height is about
4 nm.
Chang-Peng Li et. al., Appl. Phys. 100, (2006)
074318
(Right) a Typical SEM image of Fe dot array
fabricated using alumina mask anodized at 40 V
with average diameter and periodicity of 67 and
104 nm, respectively b typical SEM image of Fe
dot array fabricated using alumina mask anodized
at 25 V with average diameter and periodicity of
32 and 63 nm, respectively.
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Nanofabrication Essentials

• Bit feature fidelity (uniform diameter)
• Incredibly high density (gt 40 nm period)
• Uniform coverage over a large area
• Additionally mechanical requirements
• Arranged in circular array
• Long range order!!

Cheaper
M. Geissler and Y. Xia, Adv. Mat. 16 (2004) 1249.
J. Phys. D Appl. Phys. 35 (2002) R157-R161.
A. Moser. et.al., J. Phys. D Appl. Phys. 35
(2002) R157-R167.
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Current Technology Perpendicular Media

• Thermally stable at smaller sizes
• Easy-axis oriented out-of plane deposited on soft
  underlayer
• Higher signal to noise
• Increased read back signal
• Underlayer coupling increased
• Other recent advances
• TAC Thermally assisted recording
• AFC antiferromagnetically coupled media

(Above) Schematic representation of a magnetic
transition in AFC media.
J. Phys. D Appl. Phys. 35 (2002) R157-R161.
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Pattern Creation Lithography

• Interference lithographyfeature size down to 100
  nm
• Interference Patterned defined by lithography
• Pattern fully transferred after reactive ion
  etching
• Feature sizes are too large for discrete bits

C.A. Ross, J. Appl. Phys. 91, (2002) 6848.
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Pattern Creation Guided self-assembly

• Block copolymers have good short range order but
  lack long range order
• Solution
• Interference lithography defines trenches,
  ensuring long range order
• Block copolymer is deposited by spin casting into
  shallow grooves
• Reactive Ion Etching completes the pattern
  transfer

J. Phys. D Appl. Phys. 38 (2005) R199-R222.
Appl. Phys. Lett. 81, (2002) 3657.
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Pattern Creation Imprint Lithography

• A stamp defines the pattern
• Typical material polydimethysiloxane (PDMS) low
  adhesion and high elasticity
• But PDMS is not rigid enough for nano-scale
• Solution use PDMS as an anti-adhesion layer on a
  rigid substrate
• Immune to most resolution limits
• Feature Sizes on the order of 100nm

J. Vac. Sci. Technol. B. 15(6) (1997) 2897.
Adv. Mater. 18 (2006) 3115-3119.
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Pattern Creation Langmuir-Blodgett

• Layer-by-layer technique
• Single or sub-monolayers can be deposited one at
  a time
• Deposition occurs as the substrate is drawn
  through the film on liquid
• Mono-dispersed spheres were transferred to PDMS
  stamps via LB
• Short range order is still problematic

(left) TEM of Langmuir-Blodgett film (right) SEM
of patterned µ-dot arrays (below) AFM of µ-dot
arrays
J. Am. Chem. Soc. 125, (2003) 630-631.
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Pattern Creation Aperture Array Lithography
J. Membrane Sci. 249, (2005) 193 206.
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Summary

• Superparamagnetism places a lower limits on the
  thin film bit size
• Areal densities larger than 1 Tbit per inch2 will
  be in hard drives only if
• The manufacturing requirements can be met bit
  feature fidelity, incredibly high density (gt 40
  nm period), uniform density over a large area,
  long range order and arranged in circular array
• New techniques cost less than the established
• Nano-patterning of nanoparticles may be the
  solution
• lthttp//www.hitachigst.com/hdd/research/
• recording_head/pr/PerpendicularAnimation.htmlgt
• (or search for get perpendicular)

Outlook

• As of Oct. 17, 2007 Maximum areal density
  achieved by Western Digital with 520 Gbits per
  inch2.
• Followed by Seagate with 421Gbits per inch2 (as
  of Sept. 18 2006).
• Typical Hard drives have 200 Gbits per in2,
• as featured in WD's 250 GB WD (available since
  May 2006)

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Additional Notes

• AVS 54th International Symposium   
  Nanomanufacturing Topical Conference Wednesday
  Sessions       Session NM-WeM Invited Paper
  NM-WeM11 Nano-fabrication of Patterned Media
• Wednesday, October 17, 2007, 1120 am, Room 615
• Session Nanomanufacturing for Information
  Technologies Presenter T.-W. Wu, Hitachi Global
  Storage Technologies
• The outlook of magnetic storage technology
  predicts that, with current 40 growth rate, the
  recording areal density will hit 700 Gbits/in2
  in 2011. However, the magnetic recording physics
  also predicts that perpendicular magnetic
  recording (PMR) media will hit the thermal
  instability limit as the grain size of the
  magnetic coating scaled down below 5nm in
  diameter. Because patterned media (PM) leverages
  the geometric decoupling magnetic exchange, a
  magnetic material even with ultra-small (e.g.
  dlt5nm) but strong magnetically coupled grains can
  still be utilized to constitute the required
  recording bit (d1015nm) and avoid the thermal
  instability. Furthermore, because of its
  geometrically defined bit border, PM can achieve
  both higher track and linear densities than does
  the continuous media and hence boost the aerial
  density. As a disruptive magnetic recording
  technology, PM is viewed as one of the most
  promising routes to extending magnetic data
  recording to densities of 1 Tbit/in2 and beyond.
  The fabrication of PM disk starts with the
  imprint master mold creation followed by pattern
  replication by nano-imprinting, pattern transfer
  by reactive ion etch and finished with blank
  deposition of a magnetic coating. The key
  challenges in the PM substrate fabrication are
  how to create those nano-scaled features (e.g.
  pillars with 20nm in diameter) with acceptable
  fidelity? How to create them with an incredibly
  high density (e.g. a square lattice with less
  than 40nm in period) in a very large area (e.g.
  2 square inches) and also within a reasonable
  time frame? How to inspect them with a reasonable
  statistics basis? In addition, those features
  need to be arranged in a circular array and have
  a very stringent long range order as well.
  Although the physical feasibility at each
  critical stage has been demonstrated to a degree
  in the recent years, to ensure a manufacturing
  feasibility for the production of patterned disk
  substrates, the process robustness and
  reliability, parts longevity, high throughput
  tooling and low cost operation, etc. are still
  far from completion and remain as immense
  challenges. In order to achieve the goal of PM
  hard disk drive (HDD) production in 2011 time
  frame, many scientific innovations and technology
  advances, such as the r-? e-beam machine, guided
  self-assembly patterning, double-side high
  throughput imprinting and RIE, etc. are
  critically needed.

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Nano-Fabrication Essentials Extras
J. Phys. D Appl. Phys. 38 (2005) R199 R222.
B D Terris and T Thomson J. Physics D Applied
Physics 38 (2005) R199-R222.