Patterned media (also known as bit-patterned media or BPM[1]) is a potential future hard disk drive technology to record data in magnetic islands (one bit per island), as opposed to current hard disk drive technology where each bit is stored in 20–30 magnetic grains within a continuous magnetic film. The islands would be patterned from a precursor magnetic film using nanolithography. It is one of the proposed technologies to succeed perpendicular recording due to the greater storage densities it would enable. BPM was introduced by Toshiba in 2010.[2]
In existing hard disk drives, data is stored in a thin magnetic film. This film is deposited so that it consists of isolated (weakly exchange coupled) grains of material of around 8 nm diameter.[3] One bit of data consists of around 20–30 grains that are magnetized in the same direction (either "up" or "down", with respect to the plane of the disk). One method of increasing storage density has been to reduce the average grain volume. However, the energy barrier for thermal switching is proportional to the grain volume. With existing materials, further reductions in the grain volume would result in data loss occurring spontaneously due to superparamagnetism.
In patterned media, the thin magnetic film is first deposited so there is strong exchange coupling between the grains. Using nanolithography, it is then patterned into magnetic islands. The strong exchange coupling means that the energy barrier is now proportional to the island volume, rather than the volume of individual grains within the island. Therefore, storage density increases can be achieved by patterning islands of increasingly small diameter, whilst maintaining thermal stability.[4] Patterned media is predicted to enable areal densities up to 20–300 Tbit/in2 (3.1–46.5 Tbit/cm2) as opposed to the 1 Tbit/in2 (160 Gbit/cm2) limit that exists with current HDD technology.[5]
Differences in read/write head control strategiesedit
In existing HDDs data bits are ideally written on concentric circular tracks. This process is different in bit patterned media recording where data should be written on tracks with predetermined shapes, which are created by lithography (see below) on the disk. The trajectories that are required to be followed by the servo system in patterned media recording are characterized by a set of "servo tracks" existing on the disk. Deviation of a servo track from an ideal circular shape is called "repeatable runout" (RRO). Therefore, the servo controller in bit patterned media recording has to follow the RRO which is unknown in the time of design, and as a result the servo control methodologies used for conventional drives cannot be applied. Patterned media recording has some specific challenges in terms of servo control design:[6]
RRO profile is unknown.
RRO frequency spectrum can spread beyond the bandwidth of the servo system; therefore, it will be amplified by the feedback controller.
RRO spectrum contains many harmonics of the spindle frequency (e.g. ~ 200 harmonics) that should be attenuated. This increases the computational burden in the controller.
RRO profile is changing from track to track (i.e. it is varying).
Methods of patterned media fabricationedit
Ion beam lithographyedit
In preliminary research, one of the processes investigated for creating prototypes was ion beam proximity lithography. This uses stencil masks to produce patterns an ion-sensitive material (resist), which are then transferred to magnetic material.[7] The stencil mask contains a thin free-standing silicon nitride membrane in which openings are formed. The pattern to be generated is first formed on a substrate that contains a photo-resist using electron beam lithography. Next the substrate is used to transfer the given pattern onto the nitride membrane (stencil mask) using the process of plasma etching. To create sufficient substrates is to maintain size uniformity of the openings which is transferred to the mask during the fabrication process (etching). Many factors contribute to the achievement and maintenance of size uniformity in the mask, such as: pressure, temperature, energy (amount of voltage), and power used when etching. To optimize the process of etching uniform patterns correctly under these parameters, the substrate can be used as a template to fabricate stencil masks of silicon nitride through the process of ion proximity beam lithography. The stencil mask can then be used as a prototype to create pattern media.
In 2014, Ricardo Ruiz of Hitachi Global Storage Technologies writes in an upcoming-conference briefing note that "the most promising solution to the lithographic challenge can be found in directed self-assembly of block copolymer films which has recently evolved as a viable technique to achieve sub-20nm lithography in time for BPM technology".[8][9]
^. Toshiba.co.jp. n.d. Archived from the original on 9 November 2016. Retrieved 17 September 2014. Bit-patterned media (BPM) are a type of magnetic recording medium in which the magnetic layer is reduced to the size of one bit (one magnetic dot and space).
^"Will Toshiba's Bit-Patterned Drives Change the HDD Landscape?". PC Magazine. August 19, 2010. Retrieved August 21, 2010.
^Weller, Dieter; Mosendz, Oleksandr; et al. (July 2013). "L1 0 FePtX-Y media for heat-assisted magnetic recording: L1 0 FePtX-Y media for heat-assisted magnetic recording". Physica Status Solidi A. 210 (7): 1245–1260. doi:10.1002/pssa.201329106.
^Ross, Ca (August 2001). "Patterned Magnetic Recording Media". Annual Review of Materials Research. 31 (1): 203–235. doi:10.1146/annurev.matsci.31.1.203.
^Griffiths, Rhys (25 November 2013). "Directed self-assembly of block copolymers for use in bit patterned media fabrication". Journal of Physics D: Applied Physics. 46 (50): 503001. doi:10.1088/0022-3727/46/50/503001.
^Shahsavari; et al. (2014). Repeatable Runout Following in Bit Patterned Media Recording. ASME 2014 Conference on Information Storage and Processing Systems. pp. V001T03A001. doi:10.1115/ISPS2014-6946. ISBN978-0-7918-4579-0. S2CID 13817067. ( 2020-10-11)
^Wolfe, John C.; Pendharkar, Sandeep V.; et al. (November 1996). "A proximity ion beam lithography process for high density nanostructures". Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures. 14 (6): 3896. doi:10.1116/1.588689.
^"Magnetic Bit Patterned Media Fabrication Using Block Copolymer Directed Assembly". 2014. Retrieved 17 September 2014. The most promising solution to the lithographic challenge can be found in directed self-assembly of block copolymer films which has recently evolved as a viable technique to achieve sub-20nm lithography in time for BPM technology.
^Ross, C.A.; Cheng, J.Y. (September 2008). "Patterned Magnetic Media Made by Self-Assembled Block-Copolymer Lithography". MRS Bulletin. 33 (9): 838–845. doi:10.1557/mrs2008.179.
January 01, 1970
patterned, media, also, known, patterned, media, potential, future, hard, disk, drive, technology, record, data, magnetic, islands, island, opposed, current, hard, disk, drive, technology, where, each, stored, magnetic, grains, within, continuous, magnetic, fi. Patterned media also known as bit patterned media or BPM 1 is a potential future hard disk drive technology to record data in magnetic islands one bit per island as opposed to current hard disk drive technology where each bit is stored in 20 30 magnetic grains within a continuous magnetic film The islands would be patterned from a precursor magnetic film using nanolithography It is one of the proposed technologies to succeed perpendicular recording due to the greater storage densities it would enable BPM was introduced by Toshiba in 2010 2 Contents 1 Comparison with existing HDD technology 1 1 Differences in read write head control strategies 2 Methods of patterned media fabrication 2 1 Ion beam lithography 2 2 Directed self assembly of block copolymer films 3 See also 4 ReferencesComparison with existing HDD technology editIn existing hard disk drives data is stored in a thin magnetic film This film is deposited so that it consists of isolated weakly exchange coupled grains of material of around 8 nm diameter 3 One bit of data consists of around 20 30 grains that are magnetized in the same direction either up or down with respect to the plane of the disk One method of increasing storage density has been to reduce the average grain volume However the energy barrier for thermal switching is proportional to the grain volume With existing materials further reductions in the grain volume would result in data loss occurring spontaneously due to superparamagnetism In patterned media the thin magnetic film is first deposited so there is strong exchange coupling between the grains Using nanolithography it is then patterned into magnetic islands The strong exchange coupling means that the energy barrier is now proportional to the island volume rather than the volume of individual grains within the island Therefore storage density increases can be achieved by patterning islands of increasingly small diameter whilst maintaining thermal stability 4 Patterned media is predicted to enable areal densities up to 20 300 Tbit in2 3 1 46 5 Tbit cm2 as opposed to the 1 Tbit in2 160 Gbit cm2 limit that exists with current HDD technology 5 Differences in read write head control strategies edit In existing HDDs data bits are ideally written on concentric circular tracks This process is different in bit patterned media recording where data should be written on tracks with predetermined shapes which are created by lithography see below on the disk The trajectories that are required to be followed by the servo system in patterned media recording are characterized by a set of servo tracks existing on the disk Deviation of a servo track from an ideal circular shape is called repeatable runout RRO Therefore the servo controller in bit patterned media recording has to follow the RRO which is unknown in the time of design and as a result the servo control methodologies used for conventional drives cannot be applied Patterned media recording has some specific challenges in terms of servo control design 6 RRO profile is unknown RRO frequency spectrum can spread beyond the bandwidth of the servo system therefore it will be amplified by the feedback controller RRO spectrum contains many harmonics of the spindle frequency e g 200 harmonics that should be attenuated This increases the computational burden in the controller RRO profile is changing from track to track i e it is varying Methods of patterned media fabrication editIon beam lithography edit In preliminary research one of the processes investigated for creating prototypes was ion beam proximity lithography This uses stencil masks to produce patterns an ion sensitive material resist which are then transferred to magnetic material 7 The stencil mask contains a thin free standing silicon nitride membrane in which openings are formed The pattern to be generated is first formed on a substrate that contains a photo resist using electron beam lithography Next the substrate is used to transfer the given pattern onto the nitride membrane stencil mask using the process of plasma etching To create sufficient substrates is to maintain size uniformity of the openings which is transferred to the mask during the fabrication process etching Many factors contribute to the achievement and maintenance of size uniformity in the mask such as pressure temperature energy amount of voltage and power used when etching To optimize the process of etching uniform patterns correctly under these parameters the substrate can be used as a template to fabricate stencil masks of silicon nitride through the process of ion proximity beam lithography The stencil mask can then be used as a prototype to create pattern media Directed self assembly of block copolymer films edit In 2014 Ricardo Ruiz of Hitachi Global Storage Technologies writes in an upcoming conference briefing note that the most promising solution to the lithographic challenge can be found in directed self assembly of block copolymer films which has recently evolved as a viable technique to achieve sub 20nm lithography in time for BPM technology 8 9 See also editExchange spring media Heat assisted magnetic recording Shingled magnetic recordingReferences edit Bit Patterned Media for High Density HDDs Toshiba co jp n d Archived from the original on 9 November 2016 Retrieved 17 September 2014 Bit patterned media BPM are a type of magnetic recording medium in which the magnetic layer is reduced to the size of one bit one magnetic dot and space Will Toshiba s Bit Patterned Drives Change the HDD Landscape PC Magazine August 19 2010 Retrieved August 21 2010 Weller Dieter Mosendz Oleksandr et al July 2013 L1 0 FePtX Y media for heat assisted magnetic recording L1 0 FePtX Y media for heat assisted magnetic recording Physica Status Solidi A 210 7 1245 1260 doi 10 1002 pssa 201329106 Ross Ca August 2001 Patterned Magnetic Recording Media Annual Review of Materials Research 31 1 203 235 doi 10 1146 annurev matsci 31 1 203 Griffiths Rhys 25 November 2013 Directed self assembly of block copolymers for use in bit patterned media fabrication Journal of Physics D Applied Physics 46 50 503001 doi 10 1088 0022 3727 46 50 503001 Shahsavari et al 2014 Repeatable Runout Following in Bit Patterned Media Recording ASME 2014 Conference on Information Storage and Processing Systems pp V001T03A001 doi 10 1115 ISPS2014 6946 ISBN 978 0 7918 4579 0 S2CID 13817067 nbsp archived 2020 10 11 Wolfe John C Pendharkar Sandeep V et al November 1996 A proximity ion beam lithography process for high density nanostructures Journal of Vacuum Science amp Technology B Microelectronics and Nanometer Structures 14 6 3896 doi 10 1116 1 588689 Magnetic Bit Patterned Media Fabrication Using Block Copolymer Directed Assembly 2014 Retrieved 17 September 2014 The most promising solution to the lithographic challenge can be found in directed self assembly of block copolymer films which has recently evolved as a viable technique to achieve sub 20nm lithography in time for BPM technology Ross C A Cheng J Y September 2008 Patterned Magnetic Media Made by Self Assembled Block Copolymer Lithography MRS Bulletin 33 9 838 845 doi 10 1557 mrs2008 179 Retrieved from https en wikipedia org w index php title Patterned media amp oldid 1188347197, wikipedia, wiki, book, books, library,
