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Nośniki pamięci. Pamięci magnetyczne Suplement – nośniki informacji (przegląd). Nośniki informacji. Pamięci magnetyczne.
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Nośniki pamięci • Pamięci magnetyczne • Suplement – nośniki informacji (przegląd)
Pamięci magnetyczne A storage density of more than 200 Gigabits per square inch has been achieved in demos. Typical storage media consist of a combination of several metals, which segregate into magnetic particles embedded into a non-magnetic matrix that keeps them magnetically independent. A rectangle containing about a hundred particles makes up a bit. Their magnetic orientation is color coded in the figure below. When such a bit is imaged by a magnetic force microscope (on the right) the collection of these particles shows up as white or dark line, depending on the magnetic orientation.
Nośnik ‘perpendicular’ Generic perpendicular medium structure The structure of a typical medium for perpendicular HDD recording is shown in the Figure. 28. Apart from the change in anisotropy direction, the most significant difference is the inclusion of a thick, magnetically soft, high moment underlayer (SUL) Magnetic Nanostructures in Modern Technology, 2008
Wymagania wobec nośnika ‘perpendicular’ – Small, thermally stable grains – Narrow grain size and anisotropy distributions – High anisotropy but not so high that medium is unwritable – Controlled exchange and magnetostatic coupling to facilitate switching of individual grains – Well aligned grains CoCrPt-oxide Transmission electron micrograph of a perpendicular medium showing an average grain size of 8 nm and a distribution of σ/<dia>0.25. Magnetic Nanostructures in Modern Technology, 2008
Właściwości magnetyczne nośnika Hysteresis loop measured on a vibrating sample magnetometer at room temperature for a CoCrP-t-oxide perpendicular medium. Hn is the nucleation field, Hc is the coercivity and Hs is field required to saturate the medium. Magnetic Nanostructures in Modern Technology, 2008
Nowe trendy magnetyczne w ‘perpendicular’: nośnik typu ECC Schematic representation of exchange coupled composite (ECC) media Magnetic Nanostructures in Modern Technology, 2008
Przyszłość nośników informacji – Theoretical upper limits on data density, as function of the saturation magnetisation Ms and energy density M 7 Tb/sqi Magnetic Nanostructures in Modern Technology, 2008
Granice zapisu magnetycznego- cd The ultimate limit in data density is determined by the thermal stability of the data. The relaxation time τ of the magnetisation state of a particle can be defined as: DE is the energy barrier between the two states of magnetisation in the particle, and f0 is the frequency at which the particle attempts to change its state.The attempt frequency is related to the Larmor frequency of the magnetisation,and usually taken to be 109 Hz. The energy barrier is determined by the volume of the particle V, its magnetic anisotropy energy density K and the switching mechanism. If we assume a (theoretical) coherent rotation mechanism, the energy barrier DE = KV Magnetic Nanostructures in Modern Technology, 2008
Pomysł na idealny nośnik– struktura ‘kropkowa’ (patterned’) Magnetic Nanostructures in Modern Technology, 2008
Metody wytwarzania nośników typu ‘pattern’ Images of a 1.4×1.2 μm patterned region with a period of ∼67 nm. This was patterned by exposure to a 1 pA 30 keV Ga+ beam for 40 s. (A) AFM and (B) MFM images of the same area. (C) portion of an SEM image taken immediately after patterning. (D) Higher magnification MFM image. The dashed line grid has been added as a guide to the eye. Magnetic Nanostructures in Modern Technology, 2008
Pamięć typu M-RAM Magnetoresistive Random Access Memory
Inna koncepcja pamięci - MRAM... Magnetoresistive Random Access Memory MRAM is a memory (RAM) technology that uses electron spin to store information (based on Spintronics). MRAM has been called "the ideal memory", potentially combining the density of DRAM with the speed of SRAM and non-volatility of FLASH memory or hard disk, and all this while consuming a very low amount of power. MRAM can resist high radiation, and can operate in extreme temperature conditions, very suited for military and space applications.
Time-dependent micromagnetic simulation with random thermal fluctuations of a 4nm NiFeCo MRAM bit patterned as a 0.61.2 mm2 ellipse. The current pulse was given a 2 ns rise time, and the element reversed within 2 ns. Zapis informacji...MRAM G. Srajer et al. / Journal of Magnetism and Magnetic Materials 307 (2006) 1–31
(a) Illustration of the spin angular momentum transfer process, (b) A nanostructured thin film pillar structure with a possible spatial distribution of the horizontal-direction magnetization at atime-sliced during reversal is shown using an extended Landau–Lifshitz–Gilbert equation-based finite element numerical simulation, (c) A concentrated charge current injection through a confined area can cause magnetic excitation and spin-wave emission, MRAM... spiny G. Srajer et al. / Journal of Magnetism and Magnetic Materials 307 (2006) 1–31
Zapis informacji poprzez manipulację AFM (probe storge) One form, which is activily persued by the IBM probe storage team in Switzerland is based on a huge array of read/write probes (Fig. 68), derived from the cantilevers used in scanning probe microscopy. ultrasharp tip which can be heated, and which is used to indent holes. During writing an electrostatic force is applied between cantilever and medium. Read-outof the information is achieved by measuring the height of the cantilever above the medium. Height information is obtained by measuring the temperature of a slightly heated cantilever, which reduces as the tip sinks into a hole. Using this method, extremely high densities over 600 GBit/in2 are demonstrated (2004) Magnetic Nanostructures in Modern Technology, 2008
Zapis atomami? Atomic data storage. Each white dot is a Si atom on a 7 × 7 reconstructed Si surface. (From Bennewitz et al., 2002.) Magnetic Nanostructures in Modern Technology, 2008
Prognoza dla dysków Future recording media will be patterned !!! Magnetic Nanostructures in Modern Technology, 2008
Suplement 1 magnetyczne nośniki informacji Patterned Media Recording: the future technology for magnetic storage industry
Patterned Media Recording: the future technology for magnetic storage industry Xiaojun Zhang (Mechanical Engineering) Jie Wu (Physics) Final project of EE 235 course
Information Storage Hard disk drive (HDD) is one of the most important data storage media for electronics. Main advantage: • Big capacity. • Economical in terms of cost per bit. • Permanent (no power consuming to maintain data). HDD is NOT replaceable in modern life.
The market of HDD 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 dramatic advance of HDD September 4, 1956 Time: Name: IBM 305 RAMAC Capacity: 5 million 8-bit characters. Size: fifty 24-inch diameter disks Areal density: 2,000 bit/in2 In 2005, the areal density is Commercial HD: 100~150 Gbit/in2 Toshiba (perpendicular recording): 179 Gbit/in2 Toshiba's experimental systems: 277 Gbit/in2 Seagate Technology demonstrates: 421 Gbit/in2 Maximum of perpendicular recording technology: 1 Tbit/in2
Price of HDD, DRAM and Flash The price/performance ratio in terms of cost per bit: 1965: $10,000/MB 1989: $36/MB 1994: $1/MB 2000: 2¢/MB 2004: 0.1¢/MB 2009: 0.01 ¢/MB
The future of record media Our focus today
Hard Disk Drive http://news.bbc.co.uk/1/hi/technology/6677545.stm
Magnetic Recording Fundamentals Magnetic field http://www.ndt-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/HysteresisLoop.htm
Two Problems in Magnetic Recording • Thermal Stability Issue • Transition Jitter Noise
Thermal Stability Issue • Average Thermal Energy is kBT (KB is the Boltzmann’s constant) T normally is room temperature, ~ 300K • Energy barrier to switch a domain is KuV (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 Fluctuation Induced Magnetization Switch Magnetic Domain Magnetic Domain
Transition Jitter Noise • Transitions 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 boundary
Longitudinal Media Recording • Before 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 Recording • The 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 Recording • The 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 Layer Soft Magnetic Layer
Patterned Media Recording Comparison of conventional media recording with patterned media recording (from Hitachi)
Patterned Media Recording • In 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 Recording For the same areal density, we can get better thermal stability with patterned media recording. Typical design for a patterned media recording
Nano-fabrication approaches • Optical lithography poor spatial resolution • Focused Iron Beam not suitable for massive production • E-beam lithography low throughput • Block copolymer lithography not uniform in big scale
A candidate approach:E-beam lithography+block copolymer assembly
Encouraging result:improved uniformity & 4 times density multiplication
A key step towards massive production Patterns obtained after pattern transfer A. Cr patterns B. Si patterns
Summary • HDD 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 goal.
