Heat-assisted magnetic recording

Heat-assisted magnetic recording (HAMR) is a magnetic storage technology for greatly increasing the amount of data that can be stored on a magnetic device such as a hard disk drive.

Traditional disk drive designs are limited in the amount of data that can be stored, because there is a minimum size for a magnetic field that is used to write data. As data is stored in smaller regions on a disk, it becomes technically impossible or impractical to create a magnetic field small yet strong enough to write to a region of that size. HAMR is a technique for overcoming this limit by temporarily heating the disk material during writing, for under 1 nanosecond, which makes it much more receptive to magnetic effects and allows writing to much smaller regions (and much higher levels of data on a disk). However it was exceedingly difficult to develop, because of the extreme requirements of such a solution.

The technology was initially seen as extremely difficult to achieve, with doubts expressed about its feasibility as late as 2013.[1] The regions being written must be heated in a tiny area - small enough that diffraction prevents the use of normal laser focused heating - and requires a heating, writing and cooling cycle of less than 1 nanosecond, while also controlling the effects of repeated spot-heating on the drive platters, the drive-to-head contact, and the adjacent magnetic data which must not be affected. These challenges required the development of nano-scale surface plasmons (surface guided laser) instead of direct laser-based heating, new types of glass platters and heat-control coatings that tolerate rapid spot-heating without affecting the contact with the recording head or nearby data, new methods to mount the heating laser onto the drive head, and a wide range of other technical, development and control issues that needed to be overcome.[2][3]

As of 2018, no hard disks using HAMR are currently on the market, but HAMR is in an advanced state of pre-release development and customer testing. Seagate Technology, which has been prominent in the development of HAMR drives, first demonstrated HAMR prototypes in continual use during a 3 day event during 2015.[4] In December 2017 they announced that pre-release drives had been undergoing trials at customers during 2017 with over 40,000 HAMR drives and "millions" of HAMR read/write heads already built, and manufacturing capacity was in place for pilot volumes and first sales of production units to be shipped to key customers in 2018[3] followed by a full market launch of "20TB+" HAMR drives during 2019,[5][6] with 40TB hard drives by 2023, and 100TB drives (50 times the density at launch or 100 TB per square inch) by around 2030.[3][2]

Seagate stated that as at December 2017, HAMR development had achieved 2TB per square inch areal density (having grown at 30% per year over 9 years with a "near-future" target of 10 TBpsi), single head transfer reliability of "over 2 PB" (equivalent to "over 35 PB in a 5 year life on a 12TB drive", stated to be "far in excess" of typical use) and heating laser power required "under 200mW" (0.2 W), less than 2.5% of the 8 or more watts typically used by a hard drive motor and its head assembly.[5] Some commentators speculate that HAMR drives will also introduce the use of multiple actuators on hard drives (for speed purposes), as this development was also covered in a Seagate announcement and also stated to be expected in a similar time-scale.[6][7]

Although HAMR has not yet been released to the market, its planned successor, known as heated-dot magnetic recording (HDMR), or bit-pattern recording, is also under development, although not expected to be available until at least 2025 or later.[4][5] HAMR drives have the same form factor (size and layout) as existing traditional hard drives, and do not require any change to the computer or other device they are installed into; they can be used identically to existing hard drives.[8]

Overview

There have been a series of technologies developed to allow hard drives to increase in capacity with little effect on cost. To go beyond the limits of magnetic materials, new technologies have included perpendicular recording (PMR), helium-filled drives, shingled magnetic recording (SMR); however these all appear to have similar limitations to areal density (the amount of data that can be stored on a magnetic platter of a given size). HAMR is a technique that breaks beyond this limit with magnetic media.

The limitation of traditional as well as perpendicular magnetic recording is due to the competing requirements of readability, writeability and stability (known as the Magnetic Recording Trilemma). The problem is that to store data reliably for very small bit sizes the magnetic medium must be made of a material with a very high coercivity (ability to maintain its magnetic domains and withstand any undesired external magnetic influences).[3] The drive head must then overcome this coercivity when data is written.[3][2] But as the areal density increases, the size occupied by one bit of data becomes so small, that the strongest magnetic field able to be created for writing data with current technology is not strong enough to overcome the coercivity of the platter (or in development terms, to flip the magnetic domain), because it is not feasible to create the required magnetic field within such a tiny region.[3] In effect, a point exists at which it becomes impractical or impossible to make a working disk drive because magnetic writing activity is no longer possible on such a small scale.[3]

The coercivity of many materials happens to be very temperature dependent. If the temperature of a magnetized objects is temporarily raised above its Curie temperature, its coercivity will become much less, until it has cooled down. (This can be seen by heating a magnetized object such as a needle in a flame: when the object cools down, it will have lost much of its magnetization.) HAMR uses this property of magnetic materials to solve the problem. A very small laser within the hard drive is used to temporarily spot-heat the tiny area being written to, so that it briefly reaches a temperature where - in that tiny region - the disk's material temporarily loses much of its coercivity. Almost immediately, the magnetic head takes advantage of this to write data in a much smaller area than would otherwise be possible. The material quickly cools again and its coercivity returns, but this is now a helpful feature since it prevents the written data being easily changed until it is written again. As only a tiny part of the disk is heated at a time, the heated part cools very quickly (under 1 nanosecond[2]), and comparatively little power is needed.

The use of heating presented major technical problems, because as at 2013 there was no clear way to focus the required heat into the tiny area required within the constraints imposed by hard drive usage. The time required for heating, writing, and cooling is about 1 nanosecond which suggests a laser or similar means of heating, but diffraction limits the use of light and common laser wavelengths because these ordinarily cannot focus into anything like the small region that HAMR requires for its magnetic domains.[2] Traditional plated magnetic platters are also not suitable so new drive materials must be developed.[2] In addition a wide range of other technical, development and control issues must be overcome.[2]

Seagate state that they overcame the issue of heating focus by developing nano-scale[3] surface plasmons instead of direct laser-based heating.[2] In this method, based on the idea of a waveguide, the laser "travels" along the surface of a guiding material which is shaped and positioned to lead it to the area about to be written. Diffraction does not adversely affect this kind of wave-guide based focus, so the heating effect can be targeted to the necessary tiny region.[2] The heating issues also require media that can tolerate rapid spot-heating to over 400° C in a tiny area without affecting the contact between the recording head and the platter, or the reliability of the platter and its magnetic coating.[2] The platters are made of a special "HAMR" glass with a coating that precisely controls how heat travels within the platter once it reaches the region being heated - crucial to prevent power waste and undesired heating or erasure of nearby data regions.[2]

HAMR could eventually increase the limit of magnetic recording by more than a factor of 100. This could result in storage capacities as great as 50 terabits per square inch. Running costs are not expected to differ significantly from non-HAMR drives, since the laser only uses a few tens of milliwatts (around 1% of the common 5 to 12 watts in active use of large 3.5 inch HDDs).[1] It competes with technologies such as SMR.

Industry observer IDC stated in 2013 that "The technology is very, very difficult, and there has been a lot of skepticism if it will ever make it into commercial products", with opinions generally that HAMR is unlikely to be commercially available before 2017.[1] Seagate commented that the challenges include "attaching and aligning a semiconductor diode laser to an HDD write head and implementing near-field optics to deliver the heat", along with the scale of use which is far greater than previous near-field optic uses.[1]

History

  • In 1954, engineers of PL Corp working for RCA filed a patent which described the basic principle of using heat in conjunction with a magnetic field to record data.[9] This was followed by many other patents in this area with the initial focus on tape storage.
  • In the 1980s, a class of mass storage device called the magneto-optical drive became commercially available which used essentially the same technique for writing data to a disk. One advantage of magneto-optic recording over purely magnetic storage at that time was that the bit size was defined by the size of the focused laser spot rather than the magnetic field. In 1988, a 5.25-inch magneto-optic disk could hold 650 megabytes of data with a roadmap to several gigabytes; a single 5.25" magnetic disk had a capacity of around 100 megabytes.[10]
  • In late 1992, Sony introduced MiniDisc, a music recording and playback format intended to replace audio cassettes. Recordable MiniDiscs used heat-assisted magnetic recording but the discs were read optically via the Kerr effect.[11]
  • "late 1990s" - Seagate commenced research and development related to modern HAMR drives.[3]
  • 2006 - Fujitsu demonstrates HAMR.[12]
  • As of 2007, Seagate believed it could produce 300 terabit (37.5 terabyte) hard disk drives using HAMR technology.[13] Some news sites erroneously reported that Seagate would launch a 300 TB HDD by 2010. Seagate responded to this news stating that 50 terabit per-square-inch density is well past the 2010 timeframe and that this may also involve a combination of Bit Patterned Media.[14]
  • In early 2009 Seagate achieved 250 Gb per square inch using HAMR. This was half of the density achieved via perpendicular recording at that time.[15]
  • Hard disk technology progressed rapidly and as of January 2012, desktop hard disk drives typically had a capacity of 500 to 2000 gigabytes, while the largest-capacity drives were 4 terabytes.[16] It was recognised as early as 2000 [17] that the then current technology for hard disk drives would have limitations and that heat-assisted recording was one option to extend the storage capacity.
  • In March 2012 Seagate became the first hard drive maker to achieve the milestone storage density of 1 terabit per square inch using HAMR technology.[18]
  • In October 2012 TDK announced that they had reached a storage density of 1.5 terabit per square inch, using HAMR.[19] This corresponds to 2 TB per platter in a 3.5" drive.
  • November 2013 - Western Digital demonstrates a working HAMR drive,[20] although not yet ready for commercial sales, and Seagate states they expect to begin selling HAMR based drives around 2016.[21]
  • In May 2014, Seagate said they planned to produce low quantities of 6 to 10 TB capacity hard disks in the "near future", but that this would require "a lot of technical investment as you know, it’s also a lot of test investment". Though Seagate has not stated that the new hard disks would use HAMR, bit-tech.net speculates that they will.[22] Seagate started shipping 8 TB drives around July 2014, but without saying how that capacity was reached; extremetech.com speculates that shingled magnetic recording was used rather than HAMR.[23]
  • In October 2014, TDK predicted that HAMR hard disks could be commercially released in 2015,[24] which did not materialize.
  • At the Intermag 2015 Conference in Beijing, China, from May 11 to May 15 Seagate reported HAMR recording using a plasmonic near field transducer and high anisotropy granular FePt media at an areal density of 1.402 Tb/in².[25]
  • In October 2014, TDK, who supply hard drive components to the major hard drive manufacturers, stated that HAMR drives up to around 15 TB would probably start to become available by 2016,[26] and that the results from a prototype 10,000 rpm Seagate hard drive with a TDK HAMR head suggested that the standard 5 year durability required by enterprise customers was also achievable.
  • In May 2017, Seagate confirmed that they expect to launch HAMR drives commercially "in late 2018", and the announcement was noted by commentators as being the first time that Seagate had committed to such a specific timeframe for HAMR drive launch. Commentators at the time suggested a likely capacity at launch could be about 16TB, although specific capacities and models will not be known until launch.[27]

  • During December 2017 Seagate announced that HAMR drives had been undergoing pre-pilot trials at customers during 2017 with over 40,000 HAMR drives and "millions" of HAMR read/write heads already built, and manufacturing capacity was in place for pilot volumes in 2018 and a full market launch of "20TB+" HAMR drives during 2019.[5][6] They also stated that HAMR development had achieved 2TB per square inch areal density (growing at 30% per year over 9 years with a "near-future" target of 10 TBpsi), single head transfer reliability of "over 2 PB" (equivalent to "over 35 PB in a 5 year life on a 12TB drive", stated to be "far in excess" of typical use) and heating laser power required "under 200mW" (0.2 W), less than 2.5% of the 8 or more watts typically used by a hard drive motor and its head assembly.[5]

    Some commentators speculated on this announcement, that HAMR drives might also see the introduction of multiple actuators on hard drives (for speed purposes), as this development was also covered at a similar time and also stated to be expected in a similar time-scale.[6][7]

Thermomagnetic Patterning

A similar technology to Heat-assisted magnetic recording that has been used mainstream other than for magnetic recording is Thermomagnetic paterning. Magnetic coercivity is highly dependent on temperature, and this is the aspect that has been explored, using laser beam to irradiate a permanent magnet film so as to lower its coercivity in the presence of a strong external field that has a magnetization direction opposite to that of the permanent magnet film in order to flip its magnetization. Thus producing a magnetic pattern of opposite magnetizations that can be used for various applications [28]

Setup

There are different ways in which the setup can be made, but the underlying principle is still the same. A permanent magnetic strip is deposited on a substrate (silicon or glass), this is irradiated by a laser beam through a pre-designed mask (designed specifically for this purpose to prevent the laser beam from irradiating some portions on the magnetic film) in the presence of a very strong magnetic field (Halbach arrays have been used to produce a huge dc magnetic field [29]) The areas that are exposed/irradiated by the laser beam experience a reduction in their coercivity due to heating by the laser beam, and the magnetization of these portions can be easily flipped by the applied external field creating the desired patterns

Advantages

  • Can be used to make many types of patterns
  • Useful for magnetic recording, checkered pattern for micro and nanoscale levitation purpose
  • Cheap as the laser used typically consumes low power [30]
  • Can be easily implemented
  • Can be used for very fine details depending on the finesse with which the laser is used

Disadvantages

  • Potential loss of magnetization (if Temp. exceeds Curie temperature)
  • Superparamagnetic nature of ferromagnets at very small size limits how small one can go
  • Boundary issues due to undetermined possibilities at the reversal junction
  • Depth of reversal is currently limited [31]
  • Not too efficient on silicon substrate as silicon acts like a heat sink (better on glass substrate) [32]
  • Residual magnetization is a problem due to the depth of reversal which is limited by the penetration depth of the laser beam

See also

References

  1. 1 2 3 4 Stephen Lawson (1 October 2013). "Seagate, TDK show off HAMR to jam more data into hard drives". Computerworld. Retrieved 30 January 2015.
  2. 1 2 3 4 5 6 7 8 9 10 11 Seagate HAMR technical brief
  3. 1 2 3 4 5 6 7 8 9 http://www.guru3d.com/news-story/backblaze-on-hamr-hdd-technology.html
  4. 1 2 https://www.kitguru.net/components/hard-drives/anton-shilov/seagate-demos-hamr-hdds-vows-to-start-commercial-shipments-in-late-2017/
  5. 1 2 3 4 5 https://blog.seagate.com/intelligent/hamr-next-leap-forward-now/
  6. 1 2 3 4 https://blog.seagate.com/enterprises/multi-actuator-technology-a-new-performance-breakthrough/
  7. 1 2 https://www.anandtech.com/show/12169/seagates-multi-actuator-technology-to-double-hdd-performance : "Seagate says that the Multi-Actuator Technology is to be deployed on products in the near future, but does not disclose when exactly. As the company’s blog post on the matter mentions both MAT and HAMR, it is highly likely that commercial hard drives featuring HAMR due in late 2019 will also have two actuators on a single pivot. At the same time, it does not mean that the MAT is not going to find itself a place in products using conventional PMR."
  8. ↑ https://blog.seagate.com/intelligent/hamr-next-leap-forward-now : "HAMR is transparent to host; passed customer testing using standard code"
  9. ↑ US patent 2915594, BURNS JR., LESLIE L. & KEIZER, EUGENE O., "Magnetic Recording System", published 1959-12-01, assigned to RADIO CORPORATION OF AMERICA
  10. ↑ "ST-41200N". seagate.com. Archived from the original on March 24, 2012. Retrieved 30 January 2015.
  11. ↑ Jan Maes, Marc Vercammen. Digital Audio Technology: A Guide to CD, MiniDisc, SACD, DVD(A), MP3 and DAT. pp. 238–251. ISBN 9781136118623.
  12. ↑ "Seagate hits 1 terabit per square inch, 60TB hard drives on their way". ExtremeTech. Retrieved 30 January 2015.
  13. ↑ "Inside Seagate's R&D Labs". WIRED. 2007. Retrieved 30 January 2015.
  14. ↑ "300 teraBITS is not 300TB! And 3TB isn't 300TB!". dvhardware.net. Retrieved 30 January 2015.
  15. ↑ "Laser-Heated Hard Drives Could Break Data Density Barrier". ieee.org. Retrieved 30 January 2015.
  16. ↑ "Seagate Is The First Manufacturer To Break The Capacity Ceiling With A New 4TB GoFlex Desk Drive". seagate.com. 7 September 2011. Archived from the original on 30 January 2015. Retrieved 30 January 2015.
  17. ↑ Kryder, M.H., "Magnetic recording beyond the superparamagnetic limit," Magnetics Conference, 2000. INTERMAG 2000 Digest of Technical Papers. 2000 IEEE International , vol., no., pp. 575, 4–8 April 2005 doi:10.1109/INTMAG.2000.872350
  18. ↑ Seagate Reaches 1 Terabit Per Square Inch Milestone In Hard Drive Storage With New Technology Demonstration
  19. ↑ "[CEATEC] TDK Claims HDD Areal Density Record". Nikkei Technology Online. 2 October 2013. Retrieved 30 January 2015.
  20. ↑ "Western Digital Demos World's First Hard Drive with HAMR Technology - X-bit labs". xbitlabs.com. 13 November 2013. Archived from the original on 12 September 2014. Retrieved 30 January 2015.
  21. ↑ Bill Oliver. "WD Demos Future HDD Storage Tech: 60TB Hard Drives". Tom's IT Pro. Retrieved 30 January 2015.
  22. ↑ "Seagate hints at 8TB, 10TB hard drive launch plans". bit-tech. Retrieved 30 January 2015.
  23. ↑ "Seagate starts shipping 8TB hard drives, with 10TB and HAMR on the horizon". ExtremeTech. Retrieved 30 January 2015.
  24. ↑ "TDK: HAMR technology could enable 15TB HDDs already in 2015". kitguru.net. Retrieved 30 January 2015.
  25. ↑ High Density Heat Assisted Magnetic Recording Media and Advanced Characterization – Progress and Challenges
  26. ↑ Alexander. "TDK promises 15 TB hard drives next year". hitechreview.com. Retrieved 30 January 2015.
  27. ↑ Shilov, Anton (3 May 2017). "Seagate Ships 35th Millionth SMR HDD, Confirms HAMR-Based Drives in Late 2018". anandtech.com. AnandTech. Retrieved 18 June 2017.
  28. ↑ Thermomagnetically patterned micromagnets, F. Dumas-Bouchiat, L. F. Zanini, M. Kustov, N. M. Dempsey, R. Grechishkin, K. Hasselbach, J. C. Orlianges, C. Champeaux, A. Catherinot, and D. Givord
  29. ↑ Micromagnetization patterning of sputtered NdFeB/Ta multilayered films utilizing laser assisted heating Ryogen Fujiwaraa, Tadahiko Shinshic, Elito Kazawada
  30. ↑ Micromagnetization patterning of sputtered NdFeB/Ta multilayered films utilizing laser assisted heating Ryogen Fujiwaraa, Tadahiko Shinshic, Elito Kazawada
  31. ↑ Thermomagnetically patterned micromagnets, F. Dumas-Bouchiat, L. F. Zanini, M. Kustov, N. M. Dempsey, R. Grechishkin, K. Hasselbach, J. C. Orlianges, C. Champeaux, A. Catherinot, and D. Givord
  32. ↑ Micromagnetization patterning of sputtered NdFeB/Ta multilayered films utilizing laser assisted heating Ryogen Fujiwaraa, Tadahiko Shinshic, Elito Kazawada
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