词条 | Patterned media |
释义 |
Comparison with existing HDD technologyIn 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 Tb/in2 as opposed to the 1 Tb/in2 limit that exists with current HDD technology.[5] Differences in terms of control strategiesIn 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 (c.f. the next section) 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 which are briefly listed here:[6]
Methods of patterned media fabricationIon beam lithographyIn preliminary research, one of the processes investigated for creating prototypes was ion beam proximity lithography. Ion beam proximity lithography uses stencil masks to produce patterns in ion-sensitive material (resist) which is 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 silicone 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 filmsIn 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] See also
References1. ^{{cite web|url=http://www.toshiba.co.jp/rdc/rd/fields/11_e09_e.htm|title=Bit-Patterned Media for High-Density HDDs|date=n.d.|accessdate=17 September 2014|quote=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).}} 2. ^{{cite news | url = https://www.pcmag.com/article2/0,2817,2368023,00.asp | title = Will Toshiba's Bit-Patterned Drives Change the HDD Landscape? | publisher = PC Magazine | date = August 19, 2010 | accessdate = August 21, 2010}} 3. ^Weller et al., L10 FePtX–Y media for heat-assisted magnetic recording, (2013), 210, 7, 1245-1260, Physica Status Solidi A 4. ^Ross, C.A.: "Patterned magnetic recording media"p 203-235. Annual Review of Materials Science, 2001: 31. 5. ^{{cite journal|last1=Griffiths|first1=Rhys|title=Directed self-assembly of block copolymers for use in bit patterned media fabrication|journal=Journal of Physics D: Applied Physics|date=25 November 2013|volume=46|issue=50|doi=10.1088/0022-3727/46/50/503001}} 6. ^{{cite journal|last1=Shahsavari|title=Repeatable Runout Following in Bit Patterned Media Recording|journal=ASME 2014 Conference on Information Storage and Processing Systems|date=2014|pages=V001T03A001--V001T03A001|display-authors=etal}} 7. ^Wolfe et al.: A proximity ion beam lithography process for high density nanostructures.,(1996):.14, 3896-3899. Journal of Vacuum Science and Technology B 8. ^{{cite web|url=https://ecs.confex.com/ecs/226/webprogram/Paper43298.html|title=Magnetic Bit Patterned Media Fabrication Using Block Copolymer Directed Assembly|date=2014|accessdate=17 September 2014|quote=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.}} 3 : Computer storage technologies|Heat-assisted magnetic recording|Japanese inventions |
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