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Research paper : Creating non-volatile electronics with spintronics technology (S. Yuasa et al.)−197−Synthesiology - English edition Vol.2 No.3 (2009) performance in hard disk drives and MRAM. With an MTJ device that uses an amorphous barrier, development of an HDD recording density higher than 200 Gbit/inch2 and gigabit-class large-capacity MRAM was difficult (Fig. 4). To overcome that limitation and develop next-generation devices that have a higher integration scale, higher speed and less power consumption, even higher MR ratios were essential.First-principle theoretical calculations for a single-crystal MTJ device that uses a crystalline tunnel barrier rather than the amorphous barrier that had previously blocked further progress were published around 2001, and a huge theoretical MR ratio of over 1000 % was predicted. In 2004, AIST was the first in the world to experimentally achieve a giant room temperature TMR effect in an MTJ device using a crystalline magnesium oxide (MgO) tunnel barrier, making a great step forward in applied research on the TMR effect. Beginning with the next section of this paper, we describe the stages of Type 1 Basic Research, Type 2 Basic Research, and commercialization in the R & D of a high-performance MTJ device that uses a crystalline MgO tunnel barrier, and explain how the Full Research[4] was conducted.The Spintronics Group of the AIST Electronics Research Division did R & D on the two outcomes described below in the second research strategy period of AIST.(1) A practical next-generation magnetic head for the ultra-high-density HDDThe objective is a next-generation magnetic head for ultra-high-density HDDs that have a recording density of over 200 Gbit/inch2 to reduce power consumption by achieving an ultra-high-density, compact HDD.(2) Basic technology for ultimate non-volatile memory (spin RAM) The goal is basic spin RAM technology for the large-capacity, high-speed and highly-reliable ultimate non-volatile memory that will be the core technology for non-volatile electronics.To produce these two outcomes, we target two R & D goals: (i) development of a landmark high-performance MTJ device and (ii) development of mass production technology for it.2 Elemental technology2.1 Theory of the magnesium oxide (MgO) tunnel barrier TMR effectThis section explains the physical theory behind the TMR effect. The good crystal lattice-matching between the (001) surface of the body-centered cubic crystal (bcc) Fe and the (001) crystal surface of magnesium oxide (MgO) allows experimental fabrication of a fully epitaxial MTJ thin film that has a high quality Fe (001)/MgO (001)/Fe (001) structure. Even combining a bcc (001) electrode layer of an alloy whose main constituents are Fe and Co and a MgO (001) tunnel barrier allows formation of high-quality single-crystal MTJ thin film in the same way. In 2001, Butler et al.[5] and Mathon et al.[6] performed first-principle theoretical calculations for a single-crystal MTJ that has an Fe (001)/MgO (001)/Fe (001) structure, showing that a giant MR ratio of over 1000 % can be expected in theory. The physical mechanism of this giant TMR effect differs from that when the conventional amorphous Al-O tunnel barrier is used as described below.The difference in the electron tunneling process for the Fig. 5 (a) Hard disk drive (HDD) magnetic read head, (b) Evolution of HDD recording density and magnetic read heads Nanometer-thick insulating layer (tunnel barrier)(c)Ferromagnetic electrode layerFerromagnetic electrode layereeeeAnti-parallelstateParallelstate≡ ( ‒ )/ MR ratioElectrical resistance (R) of MTJ deviceMagnetic field (H)(d)(b)(a) Insulating layerSyF-type pinned layer(fcc (111) orientation)Seed layerFerromagnetic electrode layer (pinned layer)Ferromagnetic electrode layer (free layer)Tunnel barrierLower leadorCap layerAnti-ferromagnetic layerUpper lead0eeAPRRPAPRRPRP Nanometer-thick insulating layer (tunnel barrier)(c)Ferromagnetic electrode layerFerromagnetic electrode layereeeeAnti-parallelstateParallelstate≡ ( ‒ )/ MR ratioElectrical resistance (R) of MTJ deviceMagnetic field (H)(d)(b)(a) Insulating layerSyF-type pinned layer(fcc (111) orientation)Seed layerFerromagnetic electrode layer (pinned layer)Ferromagnetic electrode layer (free layer)Tunnel barrierLower leadorCap layerAnti-ferromagnetic layerUpper lead0eeAPRRPAPRRPRPFig. 4 Tunnel magnetoresistance (TMR) effect of magnetic tunnel junction (MTJ) device.GMR (b)Current(a) Magnetic fieldsignalMagnetic sensor device (read head)Recording track onmedium (disk)Development of next-generation head is essential for recording density above 200 Gbit/inch2TMR head(amorphous barrier)GMR headRecording density (Gbit / inch2)200620042002200019981996199419921990TMRGMRAMR10001001010.10.01Direction ofdisk rotationGMR (b)Current(a) Magnetic fieldsignalMagnetic sensor device (read head)Recording track onmedium (disk)Development of next-generation head is essential for recording density above 200 Gbit/inch2TMR head(amorphous barrier)GMR headRecording density (Gbit / inch2)Year200620042002200019981996199419921990TMRGMRAMR10001001010.10.01Direction ofdisk rotation

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