Prospects for Magnetic Recording over the next 10 years

Transcription

1 l o o k i n g i n t o t h e f u t u r e Prospects for Magnetic Recording over the next 10 years Roger Wood & Hisashi Takano Advanced Technology Hitachi GST 2004 Hitachi Global Storage Technologies Intermag 2006 San Diego 1

2 100 Years Ago Magnetic Recording Invented 1898 Valdemar Poulsen Valdemar Poulsen's wire recorder from 1898 (Danish technical museum Perpendicular? 2

3 50 Years Ago 1956 RAMAC - first HDD 5 MegaBytes Fifty 24 disks 1200 RPM 2 kbits/sq.in. 100 BPI x 20 TPI 150 kbit/s RAMAC now being restored at Magnetic Disk Heritage Center San Jose (sjmdhc.org) Al Hoagland Santa Clara University ( actually worked on a perpendicular recording follow-on to RAMAC, though it never shipped ) 3

4 25 Years Ago is this a 3380 system? system 1.26 GigaBytes (GB) Nine 14" disks 3600 RPM 12.2 Mbits/sq.in kbpi x 800 TPI 20 Mbit/s Thin-film head! Father of Perpendicular Recording Perpendicular Recording Experimental Recording Head Main pole Tohoku University First Modern Experiments 1977 PMRC2004 Website Shunichi Iwasaki 4

5 12 Years Ago % - 100% per annum areal-density growth rate! 2.5 form-factor x 12.5 mm high TravelStar LP 2.5-inch low-profile (12.5 mm) 2 disks, 4 heads, 4200 RPM Capacity 720 MB 644 Mb/sq in 101 kbpi x 6.35 ktpi 39.5 Mbits/sec thin-film media MR head PRML channel non-op. shock 500g The Magic of Scaling Shrink everything: All Head geometries (track-width, gap-length, fly-height, etc) All Media geometry (media thickness, grain-size) All Drive Electronics (Card, connector, VLSI, etc.) All Drive Mechanics (disk, slider, motor, actuator, etc.) Just a small cloud on the Horizon Magnetic viscosity in high density recording P. L. Lu and S. H. Charap. J. Appl. Phys., 75(10): , May

6 6 Years Ago % per annum areal-density growth rate! 1 GigaByte microdrive 1 GB Microdrive 1-inch form-factor (5 mm) 1 disks, 2 heads, 3600 RPM Capacity 1 GB 15.2 Gbit/sq in 435 kbpi x 35 ktpi 38.8 Mbits/sec GMR head Limit of Conventional Magnetic Recording In conclusion, conventional magnetic recording will be limited to an areal density of the order of 1 Terabit per square inch The Feasibility of Magnetic Recording at 1 Terabit per Square Inch R. Wood, IEEE Trans. Magn. Vol. 36, No. 1, Jan TMRC 99 trackwidth bit-length perpendicular medium soft underlayer 6

7 Areal Density (Gb/in 2 ) 6 Years Ago - Areal Density Growth of Areal Densities for Conventional Recording Growth Thermal Stability Limited Region Simple scaling allowed for increasing areal density for many years at 30% CGR Acceleration to % CGR thin-film head, media, channels Superparamagnetic effect Year of Introduction

8 Areal Density (Gb/in 2 ) Today - Areal Density Growth Growth of Areal Densities for Conventional Recording Thermal Stability Limited Region Simple scaling allowed for increasing areal density for many years at 30% CGR Acceleration to % CGR thin-film head, media, channels Superparamagnetic effect Superparamagnetic effect now posing a significant challenge Perpendicular + other new technologies introduced Year of Introduction Rate of increase in areal density is slowing significantly. For conventional recording technology, fundamental issues force trade-off between: Writability, Signal-to-Noise, Thermal Stability. 8

9 1 Terabit/in 2 numbers from 1999 Feasibility of Magnetic Recording at 1 Terabit per Square Inch, TMRC 99 Terabyte HDD Capacity: 1 TeraByte (8 Terabits) RPM: 23,000 (average latency: 1.3 ms) Access-Time: 2 ms average access time Data-Rate: 3 Gbits/s (375 MBytes/s) Medium: 2-layer perpendicular (with soft underlayer) H c : 12,000 Oe (1 MA/m) M r : 6360 Gauss ( 510 EMU/cc or 0.64T) Thickness: 0.36 microinches (9 nm) M r t: 0.45 memu/cm 2 grain-diameter: 8 nm ± 1nm (1-sigma) Read Head: Read-width: 1.2 microinches (30 nm) Sensitivity: 1 mv peak-peak Resistance: 50 ohms Write Head: Write-width: = 1.5 microinches (37nm) Saturation: B s = 20,000 Gauss (2 T) Disks: 8 disks of 1.3 diameter (33 mm) Media Velocity: 1600 inches/s (40 m/s) max. Mag. Spacing (top of medium): 0.26 µinch (6.5nm) Linear Density: 1.85 Mbits/inch (73 Kbits/mm) Track Density: 540 Ktracks/inch (21 Ktracks/mm) tracking accuracy =0.3 µ (7 nm) 3σ-2pass (Bit aspect ratio is 3.5:1) Channel: Detector SNR: 9.5 db (rms/rms) (allows TMRC ~ 3dB 99, system San Diego, margin) 9 August 99 Code-rate 4/5; ECC Overhead: 35% 9

10 Today: half-way to 1 Terabit/in 2 (log-scale) 10+ Gbit/sq.in. (2000) 100+ Gbit/sq.in. (2006) 1000 Gbit/sq.in. (20??) 1999 projections Areal Density = 1 Tb/in 2 Track-density = 540 ktpi Bit-density = 1850 kbpi Perpendicular Recording Simple-pole write-head write-width = 37 nm pole-tip M s = 2 Tesla GMR reader read-width = 30 nm Magnetic spacing = 6.5 nm Channel (parity + RS ECC) simple 4/5 parity + 35% ECC overhead Today s products Tb/in ktpi (need 3 to 4x increase) kbpi (need 2x increase) perpendicular now being introduced both simple-pole and trailing-shield in use - ~150 nm - ~2.4 Tesla both GMR & TMR readers in use - ~100 nm ~ nm (mainly associated with disk & ABS) parity + RS ECC just a few % assigned to parity <10% assigned to ECC (poor resolution makes it difficult for coding gain) 10

11 Terabit Head Concept vs. Today s designs IEEE Trans. Magn., Vol. 38, No. 4, pp , July 2002 US Patent (1987) commercial perpendicular head designs cusp-like designs first suggested by Akita Inst. Tech. Trailing Shield: higher field gradient, better field angles Side-shields: reduce side-fringing (adjacent track erasure) Very small flare & throat + high current maximize fields, allow high coercivity media 11

12 Today: half-way to 1 Terabit/in 2 (log-scale) 10+ Gbit/sq.in. (2000) 100+ Gbit/sq.in. (2006) 1000 Gbit/sq.in. (20??) 1999 projections: Media Grain Geometry: diameter = 8 ±1 nm height (thickness) = 9 nm interlayer = 0 nm M s = 510 EMU/cc H c0 = 12 koe Exchange - not considered in 1999! Energy barrier: E b µ 0 (H c0 -H d 2)M s V g with H d (2/3).M s Grain-limited transition (transition follows closest grain-boundary, not limited by demag etc.) Today s products: Media - Today s media is similar size but ±~2 nm - Today media is much thicker (~20nm) - Today s media has thick interlayer (~20 nm)! - Today s media is similar - Today s media is similar (short time-scale H c ) - exchange coupling acts to counteract demag. field for thermal stability and sharp transitions - relationship between Switching Field, H c0, and thermal energy barrier still not fully understood - Measurements of media noise or Jitter suggest we are getting surprisingly close to this limit 12

13 Complexity of Media Switching 1999 Thinking: These are small grains and switch as individual Stoner-Wohlfarth units (uniform rotation) The grains see just the head-field plus the demag. field (interactionfield) from the other grains 2006 Thinking: The grains can be switched via a nonuniform mode at a much lower field than simply suggested by H k or by thermal stability The grains see the head field plus the demag. field (modified by presence of pole-tip and SUL), plus an exchange field Composite Media Media Concepts CGC Media Continuous film (strongly exchangecoupled) Granular Soft underlayer Granular film (wellsegregated) 13

14 Next 10 Years? - HDD Market 1 st era 2 nd era 3 rd era 4 th era M Units Annual HDD Shipments Mainframe era 24, 14 Minicomputer era 8, 5.25 PC era Consumer era MP3 HDD since 2001 DVD/HDD recorder since

15 Areal Density (Gb/in 2 ) Next 10 Years? - Areal Density Growth of Areal Densities for Conventional Recording Thermal Stability Limited Region Simple scaling allowed for increasing areal density for many years at 30% CGR Acceleration to % CGR thin-film head, media, channels Growth Superparamagnetic effect now posing a significant challenge Perpendicular + other new technologies introduced 2016??? in 10 years Year of Introduction Rate of increase in areal density is slowing significantly. For conventional recording technology, fundamental issues force trade-off between: Writability, Signal-to-Noise, Thermal Stability. 15

16 Recent Areal Density demo Paper A4, TMRC, Aug Pittsburgh, PA Challenges for Perpendicular Write Heads at High Recording Density Yimin Hsu, Vladimir Nikitin, David Hsiao, Jianping Chen, Yi Zheng, Aron Pentek, Samuel Yuan, Michael Alex, Yansheng Luo 16

17 Future Technology Progress Technologies now being introduced but not yet fully developed: Perpendicular Recording (PMR) address thermal stability limit, allows higher areal densities expect continued advances in media and write-heads Tunnel-junction MR heads (TMR) addresses readback sensitivity: improved head SNR higher Mb/s expect continued improvement in R/R, resistance, geometry Thermal Flying-Height Control (TFC) addresses spacing control: improved resolution higher BPI expect fuller utilization with experience + new hardware & algorithms Secondary-Actuator (milli- or micro-actuator) addresses track-following: higher loop bandwidth higher TPI some server & desktop drives; expect use in smaller form-factors Channel/ECC/Format (not yet implemented in HDDs) addresses linear-density & format effic. higher capacity & reliability 4kB data-blocks, soft decision, iterative detector/decoder (e.g. LDPC) 17

18 Perpendicular Magnetic Recording (PMR) Essential to continued areal density growth Higher head fields, higher coercivity, thicker media, greater thermal stability First product introductions already in 2005 and 2006 Hitachi 2.5 perpendicular drive will reach mass production next quarter 2nd-generation perpendicular technology: improved reliability & robustness Field-Trial with 1st-generation technology started in December Positive experience; information fed back into product development Cautious introduction of new technology: new tests devised to stress and confirm robustness to external-field, disk corrosion, operating shock, etc. Considerable opportunity for further advances in technology: enhanced media, head geometry, side-shields, mag.-spacing, bit aspect ratio, etc. 18

19 Tunneling Magneto Resistance (TMR) TMR or Tunnel Junction sensors are very different to conventional GMR both in construction and in physics Current flows perpendicular to plane (CPP) from shield to shield. Electrons tunnel through an insulating barrier Tunnel barriers offer very high values of R/R (can exceed 100%!) TMR heads offer very large signals (10 s of millivolts), narrow read-gaps (higher resolution), and more conformal shields (less side-reading) Main disadvantage is high resistance - adds noise and can limit bandwidth - gets even higher for smaller devices TMR heads also exhibit shot noise from tunneling and also some 1/f noise Tunnel Junction Tunnel Junction Sensor Shield 2 Hard bias Signal Voltage (mv) Shield 1 Current flow 20 Typical quasi-static 10 transfer curve Tunnel Junction Current flow Shield Shield Track width: 80 nm Bias Volt: 140 mv Test Field (Oe) 19

20 Thermal Fly-height Control (TFC) Magnetic Spacing remains one of strongest levers for areal density Control flying height with small thermal actuator (heater) built into head Better reliability since low duty cycle (only active during read or write) Readily compensates head protrusion due to writing, temp. change, etc. Can absorb fly-height tolerances, brings head to lowest safe flying height Heating element integrated with R/W head (not to scale) Slider body Temperature rise around R/W elements Slider deformation & flying height change (exaggerated) MR reader Heater Writer Heated region Thermal expansion Disk Disk Disk 20

21 Secondary Actuator Need higher loop gain and bandwidth for more accurate track-following Mechanically stiff structures tend to compromise inertia (access time) Secondary actuator: short stroke but low moving mass & high bandwidth Implementation options & issues Type: suspension-level gimbal-level slider-level Intrinsic Bandwidth Control Electronics Compromise to mass and other stiffnesses Reliability & Cost 21

22 Iterative Soft Detection/Decoding Berrou et al.,mid-1990s Able to closely approach Shannon limit but only after many iterations and with large random, sparse code. Soft decisions successively improved by checking constraints then by message passing or belief propagation Large gains available but daunting complexity! Readback Waveform Challenge: make practical HDD implementation while retaining some of promised gain known recording-channel characteristics log 10 (sector error rate) improved decisions from trying to satisfy channel response Soft Detector soft info many iterations soft info Soft Decoder improved decisions from trying to satisfy parity checks BCJR 4k LDPC Conventional detector & RS code 1.5 db gain simulation SNR (db) (arbitrary offset) known parity-code constraints Final Data BCJR detector 4k LDPC code 10x10 iterations PW50/T = 2.5 mixed noise 22

23 Limits to Areal Density Growth Exchange Coupled Composite Media for Perpendicular Magnetic Recording, R. H. Victora & X. Shen (Minnesota), IEEE Trans. Magn., Vol. 41, No. 10, pp , Oct (High-Hk, low-ms) / (Low-Hk, high-ms) Controlled top/bottom exchange H0 = 12.8 koe Exchange Spring Recording Media for Areal Densities up to 10 Tbit/in², D. Suess et al. (Vienna), Appl. Phy. Letters, vol. 87, (2005) High/Low/High anisotropy sandwich Grain-size: 3 nm sq. x 18 nm tall H0 = 11 koe KuV/kT = 56 ECC 1 Terabit Medium controlled exchange 10 Terabit Medium? ~5 nm dia. grain 5 nm (high-h k ) 10 nm (high M s ) 2 x 2 nm grain FePt 2 nm (high-h k ) Fe3Pt 14 nm (soft) FePt 2 nm (high-h k ) 23

24 Areal Density (Gb/in 2 ) Next 10 Years? - Areal Density Growth of Areal Densities for Conventional Recording Thermal Stability Limited Region Simple scaling allowed for increasing areal density for many years at 30% CGR Acceleration to % CGR thin-film head, media, channels Growth Superparamagnetic effect now posing a significant challenge Perpendicular + other new technologies introduced 2016 Year of Introduction Conventional Recording technology Aggressive engineering pushing areal density towards thermal & signalprocessing limits ~1 Tbit/sq.in Rate of increase in areal density is slowing significantly. For conventional recording technology, fundamental issues force trade-off between: Writability, Signal-to-Noise, Thermal Stability. 24

25 Beyond Conventional Recording Two favorite technology options to extend thermal limit Patterned Media (1 large grain per bit) Thermal Assist (Very high Anisotropy) 1 bit = 1 island HAMR Read GMR Sensor laser write coils high anisotropy medium sensitive to temperature heat spot deposition islands Challenges: Disk Manufacture Lithography/Stamping Challenges: Head Integration New Media Development plus all the engineering challenges of scaling dimensions for >Terabit/in 2! 25

26 Areal Density (Gb/in 2 ) Next 10 Years? - Areal Density Growth of Areal Densities for Conventional Recording Thermal Stability Limited Region Simple scaling allowed for increasing areal density for many years at 30% CGR Acceleration to % CGR thin-film head, media, channels Growth? Superparamagnetic effect now posing a significant challenge Perpendicular + other new technologies introduced Year of Introduction Recording technology changes to Patterned and/or HAMR and/or Solid-State and/or Other?

27 Conclusions / Summary Recent Products have reached approximately 130 Gbit/sq.in. Laboratory Demonstrations have been reported at Gb/sq.in. Continued advance is assured because of further opportunities in recently introduced technologies, PMR, TMR, TFC, & Secondary Actuator, plus future improvements in detection and decoding Limit for Conventional Recording is approximately 1 Terabit/sq.in. Thermal considerations force lower limit on grain-size ( but relationships between switching field, thermal limit, media noise not fully understood) Very major engineering improvements will be required to approach 1 Tb/in 2 (magnetic-spacing, interlayer thickness, side-shielding for reader & writer, read sensitivity, track-following, powerful detector & error correction, better format efficiency, long data blocks, etc.) Alternate Technologies (especially Patterned Media & HAMR) will be vying over the next 10 years to replace conventional recording in the marketplace. Deciding factors will be cost, performance, reliability 27

28 2004 Hitachi Global Storage Technologies All Rights Reserved, Copyright(C) Intermag , Hitachi, May 10, Ltd

29 Intermag 06: Session CA (Wednesday Morning) SYMPOSIUM ON DATA STORAGE DEVICES IN 10 YEARS: HDD OR SOLID STATE? Bruce Terris, Chair, HGST 9:00 CA-01. Prospects for Magnetic Recording over the next 10 years. (Invited) R.W.Wood and H. Takano HDD AdTech, Hitachi GST, San Jose, CA, USA 9:30 CA-02. Heat Assisted Magnetic Recording. (Invited) B. Rottmayer, W.A. Challener, J. Hohlfeld, B. Lu, C. Mihalcea, C. Peng, T. Rausch and S.A. Seigler Seagate Research, Pittsburgh, PA, USA 10:00 CA-03. Recent Progress in Patterned Magnetic Recording Media. (Invited) A. Kikitsu, Y. Kamata, M. Sakurai and K. Naito Storage Materials & Devices Laboratory, Toshiba Corp., Corporate R&D Center, Kawasaki, Kanagawa, Japan 10:30 CA-04. Solid State Storage, Limits of Flash Memory. (Invited) A. Fazio Intel, Santa Clara, CA, USA 11:00 CA-05. The Future Prospect of Semiconductor Nonvolatile Memory. (Invited) K. Kim Semiconductor R & D Center, Memory Business, Samsung Electronics Co, Yongin-City,, Kyungki-Do, South Korea 11:30 CA dimensional data storage in magnetic nanowire networks. (Invited) R.P. Cowburn Blackett Physics Laboratory, Imperial College London, London, United Kingdom 29

30 Published Digest Prospects for Magnetic Recording over the next 10 years Roger Wood and Hisashi Takano Hitachi Global Storage Technologies, San Jose, California, USA This paper examines recent progress in magnetic recording and draws upon a variety of sources in presenting the outlook for the next ten years. The discussion is confined to conventional longitudinal and perpendicular magnetic recording where we assume a featureless medium and no thermal assist (i.e. patterned media and 'HAMR' are excluded). The traditional measure of technology progress for data storage is areal density in bits/inch2. Recent products exceed 100 Gbit/in2 and with a rate of increase approaching 40% per annum. If this rate were to be sustained over 10 years, we would reach approximately 10 Terabits/in.2 - far exceeding even the most optimistic projections of the densities that can be supported by conventional technology! Recent advances, however, are very encouraging with respect to our ability to approach 1 Terabit/in.2 and the figure below shows a simple projection towards this asymptotic value. Our optimism about the extendibility of conventional recording is based both on the recent successful introduction of several important new technologies into products as well as the outlook for continued improvements in the media, head, servo-mechanics and signal processing. Recent products are seeing, for example, the use of perpendicular recording, tunnel-mr readers, thermal fly-height control, and secondary actuators (not necessarily all in the same product yet). Significant further improvements can be expected in 'second generation' implementations of all of these technologies. 30

31 Digest Areal Density (Gb/in 2 ) Growth of Areal Densities for Conventional Recording Thermal Stability Limited Region Simple scaling allowed for increasing areal density for many years at 30% CGR Acceleration to % CGR thin-film head, media, channels Superparamagnetic effect now posing a significant challenge Perpendicular + other new technologies introduced Year of Introduction Recording technology changes to Patterned and/or HAMR and/or Solid-State Rate of increase in areal density is slowing significantly. For conventional recording technology, fundamental issues force trade-off between: Writability, Signal-to-Noise, Thermal Stability. The most dramatic recent introduction is the use of a perpendicular recording which involves changes in the medium, the head and the signal processing. The ability to write sharp transitions in a relatively thick high-coercivity recording layer has allowed the fundamental thermal (superparamagnetic) limit to be pushed back considerably. Assuming that all the supporting technologies can be scaled, estimates for the ultimate limit for a perpendicular recording system range from 500 Gb/in.2 to 1 Terabit/in.2. [1,2]?

32 Digest The difficulties of scaling the 'supporting technologies' must not be underestimated. The most critical of these are the magnetic spacing from head to recording layer, the field-strength and gradient of a narrow-track writer and the sensitivity and resolution of a narrow-track reader, the servo-mechanical system for accessing/following very narrow tracks, and the signal processing that must deliver reliable data at low signal to noise ratio. The ability to control flying height on an individual head must rank as one of the most important innovations. Traditionally flying-heights (and magnetic spacing) are set conservatively to accommodate the worst-case tolerances (fabrication, mechanical, temperature, altitude, etc.) and to absolutely avoid significant head-disk interference and catastrophic failure. With the use of thermal fly-height control (TFC), most of these tolerances can be eliminated. The target for 'Terabit' mag.-spacings is 5 to 6.5 nm and serious experiments are being conducted to approach this regime [3]. The geometry of the write head and associated shields as well as the characteristics of the soft-underlayer in the medium must be jointly optimized to obtain good results on very narrow tracks while minimizing off-track effects. Modern processing techniques allow these very complex head structures to be fabricated with remarkable accuracy in three dimensions [4]. Also recent CPP (current perpendicular to plane) readers are showing dramatically higher DR/R sensitivity while constraining resistance to a more acceptable range. 32

33 Digest Commensurate advances are occurring in servo-mechanical and signal-processing arenas. High-bandwidth secondary actuators will allow tighter track-following. Longer data blocks and iterative detection are promising operation at lower signal-to-noise ratios. Together these advances in technology will ensure that the data storage business will be dominated over at least the next five years by 'conventional' magnetic recording technology. To maintain areal density growth beyond this time-frame will require 'next generation' technologies such as patterned media and 'HAMR'. These are very challenging major technology changes, as will be discussed later in this session [5]. References [1] M. Mallary, et al. "One terabit per square inch perpendicular recording conceptual design." IEEE Trans. Magn., Vol. 38, No. 4, pp , July 2002 [2] H. Muraoka et al., "Development of High Density Perpendicular Recording Channel", Intnl. Symp. on Ultra-High Density Spinic Storage Systems, Sendai, Japan, Oct [3] M. Mate et al., "Will the numbers add up for sub-7-nm magnetic spacings? Future metrology issues for disk drive lubricants, overcoats, and topographies" IEEE Trans. Magn., Vol. 41, No. 2, pp , Feb [4] R. Fontana et al. "E-beam writing: a next-generation lithography approach for thinfilm head critical features" IEEE Trans. Magn., Vol. 38, No. 1, pp , Jan [5] Symposium on "Data storage devices in 10 years: HDD or Solid State?" Intermag 2006, San Diego CA, May 8-12,