Patterned Media Recording: the future technology for magnetic storage industryInformation StorageSlide 3The dramatic advance of HDDMoore’s lawPrice of HDD, DRAM and FlashTrends dominated by technologyThe future of record mediaHard Disk DriveMagnetic Recording FundamentalsTwo Problems in Magnetic RecordingThermal Stability IssueTransition Jitter NoiseLongitudinal Media RecordingPerpendicular Media RecordingSlide 16Patterned Media RecordingSlide 18Slide 19Nano-fabrication approachesA candidate approach: E-beam lithography +block copolymer assemblyEncouraging result: improved uniformity & 4 times density multiplicationA key step towards massive productionSummaryPatterned Media Recording: the future technology for magnetic storage industryXiaojun Zhang (Mechanical Engineering)Jie Wu (Physics)Final project of EE 235 courseInformation StorageHard disk drive (HDD) is one of the most important data storage media for electronics.Main advantage:1. Big capacity. 2. Economical in terms of cost per bit.3. Permanent (no power consuming to maintain data).HDD is NOT replaceable in modern life.In 1999, sales of hard drives reaches US $32 billion.In 2007, the 2 biggest HD oems - Seagate and Western Digital collectively reported an annual HD revenue of nearly $17 billion.An a substantial improvement of magnetic storage could enable entirely new computing applications, with spillovers across the computer industry and every industry that uses magnetic recording to store data.Example of how fast a new technology is adopted by this industry:The market of HDDTime: September 4, 1956Name:IBM 305 RAMAC Capacity: 5 million 8-bit characters.Size: fifty 24-inch diameter disksAreal density: 2,000 bit/in2In 2005, the areal density isCommercial HD: 100~150 Gbit/in2Toshiba (perpendicular recording): 179 Gbit/in2 Toshiba's experimental systems: 277 Gbit/in2Seagate Technology demonstrates: 421 Gbit/in2Maximum of perpendicular recording technology: 1 Tbit/in2The dramatic advance of HDDMoore’s lawThe price/performance ratio in terms of cost per bit:1965: $10,000/MB1989: $36/MB1994: $1/MB 2000: 2¢/MB2004: 0.1¢/MB2009: 0.01 ¢/MBPrice of HDD, DRAM and FlashTrends dominated by technologyThe future of record mediaOur focus todayHard Disk Drivehttp://news.bbc.co.uk/1/hi/technology/6677545.stmMagnetic Recording Fundamentals http://www.ndt-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/HysteresisLoop.htmMagnetic fieldTwo Problems in Magnetic Recording Thermal Stability IssueTransition Jitter NoiseAverage Thermal Energy is kBT (KB is the Boltzmann’s constant)T normally is room temperature, ~ 300KEnergy barrier to switch a domain isKuV(V is the volume of the domain;Ku is the anisotropy constant of the material. Higher Ku means higher writing magnetic field)KuV/kBT demtermines the thermal stability.Normally it should be larger than 60.Thermal Stability IssueMagnetic Domain Magnetic DomainThermal Fluctuation InducedMagnetization SwitchTransition Jitter NoiseTransitions meanders between random grains.This transition jitter causes noise.More grains at the boundary can make the transition smoother, and thus reduce noise.Normally, for each bit cell, there must be 100 or more grains to get good signal-to-noise ratio (SNR).Transition boundaryLongitudinal Media RecordingBefore 2005, HDDs were made by longitudinal recording. However, as the bit size becomes smaller and smaller, thermal instability becomes a problem. (KuV/kBT)The magnetization of each bit is directed along the disk surface.This head-to-head or tail-to-tail structure makes them unstable against thermal fluctuation.Since it uses fringing field, which is normally smaller than gap field. Materials with high Ku can not be used.Perpendicular Media RecordingThe first commercially available disk drive with a diameter of 1.8" was produced by Toshiba in 2005. Soon after that in January 2006, Seagate Technology began its first laptop sized 2.5-inch hard drive.Most recently in February 2009 Seagate Technology announced the first 7200 rpm 2.0 Terabyte Hard Drive using PMR technology.Perpendicular Media RecordingThe bits in perpendicular recording are magnetized up or down perpendicular to the disk surface. With the combination of soft magnetic underneath, perpendicular recording technology realized the use of gap field. Materials with higher Ku can be used to circumvent the thermal instability problem. (KuV/kBT) Recording LayerSoft Magnetic LayerPatterned Media RecordingComparison of conventional media recording with patterned media recording (from Hitachi)Patterned Media RecordingIn conventional recording techniques, if we increase grain volume V, the noise due to transition jitter will increase accordingly. In patterned media recording, the magnetic bits are perfectly patterned and isolated from each other. Therefore the jitter problem can be reduced.Each island is a single magnetic domain. Patterned media is therefore thermally stable.Since we only need one grain for each bit instead of 100 grains, the areal density can be increased roughly by 100 times with the same thermal stability.Patterned Media RecordingFor the same areal density, we can get better thermal stability with patterned media recording.Typical design for a patterned media recordingNano-fabrication approachesOptical lithography poor spatial resolutionFocused Iron Beamnot suitable for massive productionE-beam lithographylow throughputBlock copolymer lithographynot uniform in big scaleA candidate approach:E-beam lithography+block copolymer assemblyEncouraging result:improved uniformity & 4 times density multiplicationA key step towards massive productionA. Cr patternsB. Si patternsPatterns obtained after pattern transferSummaryHDD experience dramatic development for the last 50 years and will keep this trend as Moore’s law requires.The development of HDD is generated by the emerging and adoption of new technologies.Patterned Media Record is the future technique to replace longitudinal and perpendicular media recording.Nano-fabrication technique is the key to realize our
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