Future Materials Research in Data Storage NSF Workshop on Cyberinfrastructure for Materials Science Mark H. Kryder CTO and Sr. Vice President, Research, Seagate Technology University Professor, Carnegie Mellon University

Mark H. Kryder NSF Workshop Page 2 Outline  Recording Overview  Materials Problems in Future Recording Technologies  Perpendicular Recording  Heat Assisted Magnetic Recording  Bit Patterned Media  TGMR/GMR Readers  Multiferroics  Discussion of Modeling Needs

Mark H. Kryder NSF Workshop Page 3 Disc Drives Today Cover the Widest Range of Users and Systems Ever Handheld Gaming DVR NotebookDesktop Enterprise 12 GB 750 GB 160 GB 73 GB 300 GB 750 GB Low-cost, high-capcity, disk drives are enabling new devices, resulting in rapid growth of the storage industry and the emergence of new industries. e.g. Apple iPod, PVR’s, X-Box, automobile navigation systems, digital video cameras, etc.

Mark H. Kryder NSF Workshop Page 4 Areal Density Growth Single particle superparamagnetic limit (estimated) Charap’s limit (broken) Late 1990s – super paramagnetic limit demonstrated through modeling Longitudinal recording reaching areal density limits Perpendicular expected to extend to Tb/in 2 Additional innovations required at that point heat-assisted recording (HAMR) bit patterned media (BPM) recording Areal Density CAGR 40% Transfer Rate CAGR 20% Perpendicular HAMR HAMR+ BPM

Mark H. Kryder NSF Workshop Page 5 Magnetic domains oriented in the direction of travel of the head. Longitudinal Recording Perpendicular Recording Soft underlayer “mirrors” write head and makes it possible to write domains much closer together.

Mark H. Kryder NSF Workshop Page 6 Magnetic Media Evolution Physical grain size below 10 nm

Mark H. Kryder NSF Workshop Page 7 HAMR can theoretically extend areal density beyond 10 Tbpsi

Mark H. Kryder NSF Workshop Page 8 YCo 5 HAMR Potential  Ability to record on media with anisotropy beyond writability with current perpendicular recording technology  Increased resolution with cross- and in-track thermal gradient recording  HAMR freezing dynamics allowing more intergranular exchange and unique composite media designs. 10× AD gain potential with FePt 10 nm Dieter Weller SmCo 5

Mark H. Kryder NSF Workshop Page 9 HAMR Head Disc Interface Material Needs Media Overcoat (< 2 nm) and Lubricant must be able to withstand the repeated exposure to the high writing temperature. New media overcoat materials will be needed. Carbon overcoat can be damaged and/or graphitized at much lower temperature than its 560°C oxidation temperature. New Disc Lubricant materials will be required. 120mJ/cm 2 Media DLC is removed HDI

Mark H. Kryder NSF Workshop Page 10 Bit Patterned Media Lithography vs. Self Organization Lithographically Defined Major obstacle is finding low cost means of making media At 1 Tbpsi, assuming a square bit cell and equal lines and spaces, 12.5 nm lithography would be required Semiconductor Industry Association roadmap does not provide such linewidths within the next decade Direct E-Beam Write or Di-Block Co-Polymer Idea: Use Pattern Assisted Assembly to establish circumferential tracks on discs FePt Self-Organizing Media 130 nm 6 nm FePt particles “9 Tb/in 2 “ ~mm

Mark H. Kryder NSF Workshop Page 11 Di-Block Co-polymer Template A B LoLo Guiding patterns can provide long range order controlled 2D alignment to guiding patterns balance polymer-interface vs polymer-substrate interactions Block-copolymers form naturally ordered nano-structures A-B block copolymer precursor substrate control of vertical orientation on any substrate improve long-range order and uniformity selective removability of one component reduce L 0 without losing uniformity, order use of “environmentally safe” chemicals Use as a template for pattern transfer additive process (fill in holes by plating): - ensure open contact to metal substrate - ensure all pores get filled equally subtractive process (transfer down by RIE): - etching requires high etch-resistive resist lines dots

Mark H. Kryder NSF Workshop Page 12 Self Organized Magnetic Array Media Important Research Topics: Particle Size and Distribution Control Eliminate Sintering / Coarsening during anneal e.g. FCC-FCT (A1 – L1 0 ) Phase Transformation Magnetic Easy Axis Orientation Registered Large Scale Assembly Packing density Tribology D p : smallest possible thermally stable magnetic grain core size! S. Sun, Ch. Murray, D. Weller, L. Folks, A. Moser, Science 287, 1989 (2000). 130 nm e.g. 6 nm FePt particles 1 particle/bit~“9 Tb/in 2 “ ~m~m

Mark H. Kryder NSF Workshop Page 13 TGMR/GMR Reader Materials Top Shield Magnet FL AFM/SAF/RL Bottom Shield Insulator Current Flow Electron Flow FL RL Tunneling Barrier Flux from the media rotates reader free layer magnetization thus changing spin polarized electron tunneling conduction. Media Field Output Voltage FL-RL FL Linear Range Operate in the linear range of transfer function. Sensitivity (slope) is determined by TMR  Alternate Barrier TGMR (MgO)  Improved amplitude, and lower RA  Potential to extend TGMR reader to area density  Current problem – Maintaining soft magnetic property of free layer, while keeping high DR/R and low RA.  CCP Design (current confined path)  A discontinuous oxide buried in metal  Higher DR/R and RA as compared to CPP Spin Value  Potential to use for area density of 400~ 600Gb/In2.  Current problem – Reducing variation of RA, and DR/R, and increasing DR/R.  CPP Spin Valve With Metal or Half Metal Spacer  Could offer better reliability, and SNR at very high KTPI  Potential to use for area density of 600Gb/In2 and behind  Current problem – Concept not proven, and processing half metals at temperature magnetic head can tolerate difficult AFM Pinned Layer Ru Ref. Layer Free Layer AFM Pinned Layer Ru Ref. Layer Cu Free Layer AFM Pinned Layer Ru Ref. Layer MgO Free Layer Reader Development Approaches

Mark H. Kryder NSF Workshop Page 14 Multiferroic Data Storage System  Readback is difficult from PE media, due to free charges, but not from FM media.  Generating enough magnetic field to write to thermally stable FM media is difficult.  An electric field can be used to assist writing by by using a media that is both PE and FM (Multiferroic). The data could then be read back using an MR head.  Both single phase and multiferroic materials exist, but composite materials are most interesting due to their higher transition temperatures (both PE & FM above RT). A composite material is achieved by combining MS and PE materials [ex. BiFeO 3 - CoFe 2 O 4 or BaTiO 3 -CoFe 2 O 4 ]. An electric field applied to the composite will induce strain in the PE constituent which is passed along to the MS constituent, where it induces a change in the magnetic anisotropy. V+ V- V+ V- I Diagram of an Example Recording System P P M P P M P P M P P M

Mark H. Kryder NSF Workshop Page 15 Computing Needs in Magnetic Recording Technology  Micromagnetic models of media structure with 3-10 nm grain size and variable exchange coupling at the grain boundaries that allow us to understand the recording of 10’s to 1000’s of bits involving grains each.  Models which enable prediction of magnetic materials properties and processes for making them that enable growth of materials with variable grain sizes, variable magnetic parameters, and variable exchange coupling across grain boundaries.  Models of tribological properties of thin film (<2 nm) materials.  Models of self organization in diblock copolymers and in magnetic nanoparticle arrays.  Predictions of improved giant and tunneling magnetoresistive materials.  Predictions and understanding of multiferroic materials.  NUMEROUS OTHERS!!