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Department of Electronics

Nanoelectronics 12. Atsufumi Hirohata. Department of Electronics. 12:00 21/ February/ 2014 Friday (D/ L 002). Quick Review over the Last Lecture. Origin of magnetism :. ( Circular current ) is equivalent to a ( magnetic moment ). Dipole moment arrangement :. Paramagnetism.

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Department of Electronics

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  1. Nanoelectronics 12 Atsufumi Hirohata Department of Electronics 12:00 21/February/2014 Friday (D/L 002)

  2. Quick Review over the Last Lecture Origin of magnetism : ( Circular current ) is equivalent to a ( magnetic moment ). Dipole moment arrangement : Paramagnetism  (TN) : Néel temperature Antiferromagnetism AFM PM Ferromagnetism  (TC) : Curie temperature Ferrimagnetism FM PM

  3. Contents of Nanoelectonics I. Introduction to Nanoelectronics (01) 01 Micro- or nano-electronics ? II. Electromagnetism (02 & 03) 02 Maxwell equations 03 Scholar and vector potentials III. Basics of quantum mechanics (04 ~ 06) 04 History of quantum mechanics 1 05 History of quantum mechanics 2 06 Schrödinger equation IV. Applications of quantum mechanics (07, 10, 11, 13 & 14) 07 Quantum well 10 Harmonic oscillator 11 Magnetic spin V. Nanodevices (08, 09, 12, 15 ~ 18) 08 Tunnelling nanodevices 09 Nanomeasurements 12 Spintronic nanodevices

  4. 12 Spintronic Nanodevices • Magnetoresistance • Hard disk drive • Magnetic random access memory • Spin-polarised three-terminal devices

  5. Recent Progress in Magnetoelectronics I - Giant Magnetoresistance * After K. Inomata, J. Magn. Soc. Jpn.23, 1826 (1999).

  6. Discovery of Giant Magnetoresistance H = 0 H = Saturation Giant magnetoresistance ( GMR ) : [ 3 nm Fe / 0.9 nm Cr ]  60 * MR Spin-valve “OFF” MR Ratio Spin-valve “ON” 50 % resistance change at 4.2 K * M. N. Baibich et al., Phys. Rev. Lett.61, 2472 (1988); P. Grünberg et al., Phys. Rev. Lett.57, 2442 (1986).

  7. How Can We Find a Hard Disc Drive ? Open your computer … This is a HDD !

  8. Do NOT Try This at Home ! Magnet Arm Platter Open a metal frame of a HDD … ・Arm is operated by a linear motor with a very strong permanent magnet. - Arm moves ~ 100 times/sec. - Platter records data. - Platter rotates 5400 ~ 15000 rpm.

  9. Where Can We Find a Hard Disc Drive ? Hard disc recorder Video game PC GPS navigation Video camera Digital camera PDA Data storage Mobile phone mp3 player Most popular recording media now : ・Cheap ・Random access ・Large capacity ・High speed ・Non-volatility ・Infinite usage

  10. HDD Operation

  11. HDD Writing / Reading Operation HDD writing operation : HDD reading operation :

  12. Aerial Density Increase by GMR Introduction Superparamagnetic limit Aerial density growth of hard disk drives : 60 % / yr. with GMR heads 30 % / yr. with AMR heads * D. A. Thompson et al., IBM J. Res. Develop44, 311 (2000).

  13. Computer Operation In a computer, data is transferred from a HDD to a Dynamic Random Access Memory : Data stored in a capacitor.  Electric charge needs to be refreshed.  DRAM requires large power consumption. * http://www.wikipedia.org/

  14. Gap between HDD and DRAM A gap between data storage and operation : * http://agigatech.com/blog/page/2/

  15. Flash Memory In 1980, Fujio Masuoka invented a NOR-type flash memory : • 1 byte high-speed read-out • Low writing speed • Flash erase for a unit block ( 1 ~ 10 kbyte ) only ! • Difficult to integrate In 1986, Fujio Masuoka invented a NAND-type flash memory : • No 1 byte high-speed read-out • High writing speed • Ideal for integration * http://rikunabi-next.yahoo.co.jp/tech/docs/ct_s03600.jsp?p=000500 * http://www.wikipedia.org/

  16. Solid State Drive with Flash Memory Solid state drive (SSD) started to replace HDD : pureSi introduced 2.5” 1-TB SDD in 2009 : • Data transfer speed at 300 MB/s • Slow write speed For example, a system with a units of 2kB for read / out and 256 kB for erase : in order to write 1 bit, the worst case scenario is • 128 times read-out • 1 time flash erase • 128 times re-write

  17. HDD vs Flash Memory Demand for flash memories : Price of flash memories : * http://www.manifest-tech.com/ce_products/flash_revolution.htm

  18. Advantages of MRAM * After K. Inomata, J. Magn. Soc. Jpn.23, 1826 (1999).

  19. Magnetic Random Access Memory Basic operation of magnetic random access memory (MRAM) : * S. S. P. Parkin, 1st Int'l Sch. on Spintronics and Quantum Info. Tech., May 13-15, 201 (Maui, HI, USA).

  20. MRAM Demonstration Freescale (now EverSpin Technologies) 4 Mbit MRAM : * http://www.freescale.com/ ** http://www.chipworks.com/blogs.aspx?id=2514

  21. Improved MRAM Operation Required writing currents for several techniques dependent upon cell size: Ampère-field-induced magnetisation reversal with a ferromagnetic overlayer (Current technology) Ampère-field-induced magnetisation reversal without a ferromagnetic overlayer (Current technology) Current-induced magnetisation reversal JC ~ 10 7 A / cm 2 (Current technology) Write current (mA) Current-induced magnetisation reversal JC ~ 10 6 A / cm 2 Current-induced magnetisation reversal JC ~ 5  10 5 A / cm 2 MRAM cell size (µm) * S. Nakamura, Y. Saito and H. Morise, Toshiba Rev. 61, 40 (2006).

  22. Current-Induced Magnetisation Reversal Anti-parallel (AP)  parallel (P) reversal in a GMR / TMR junction : Spin-transfer torque ** * M. Oogane and T. Miyazaki, “Magnetic Random Access Memory,” in Epitaxial Ferromagnetic Films and Spintronic Applications, A. Hirohata and Y.Otani (Eds.)(Research Signpost, Kerala, 2009) p. 335. ** J. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996); L. Berger, Phys. Rev. B 54, 9353 (1996).

  23. Recent Progress in Magnetoelectronics II - Tunnel Magnetoresistance * After K. Inomata, J. Magn. Soc. Jpn.23, 1826 (1999).

  24. Spin-Dependent Electron Tunneling Atom 1 Barrier Atom 2 r(r ) 3d 4p 4s r Jullière's model : FM / insulator / FM junctions * * M. Jullière., Phys. Rep.54A, 225 (1975).

  25. TMR for Device Applications NOT following Jullière's model : ** TMR =2P1P2/(1-P1P2) ** S. S. P. Parkin, 1st Int'l Sch. on Spintronics and Quantum Info. Tech., May 13-15, 2001 (Maui, HI, USA). Recent progress in TMR ratios : > 400 % TMR ratio has been achieved !  > Gbit MRAM can be realised. * M. Jullière., Phys. Rep.54A, 225 (1975).

  26. Improved Tunnel Barriers Epitaxial (oriented) barriers : * 1 2 , 5 1 2 , 5 • Disorder at the interface : • FM over-oxidation • lattice defects Defects in the barrier • Disorder at the interface : • FM over-oxidation • lattice defects • island growth of the barrier Conventional amorphous barriers : * * After S. Yuasa et al., 28th Annual Conference on Magnetics, Sep. 21-24, 2004 (Okinawa, Japan).

  27. Recent Progress in Spintronics * After K. Inomata, J. Magn. Soc. Jpn.23, 1826 (1999).

  28. Spin-Polarised Three-Terminal Devices Gate Voltage Input Output * After M. Johnson, IEEE Spectrum37, 33 (2000).

  29. Major Spin-Polarised Three-Terminal Devices

  30. Spin Valve / Magnetic Tunnel Transistors Magnetic tunnel transistor : † Spin valve transistor : * Combining semiconductor with GMR / TMR devices :  First step towards all metal devices * R. Sato and K. Mizushima, Appl. Phys. Lett.79, 1157 (2001); D. J. Monsma et al., Science281, 407 (1998); † S. S. P. Parkin, 1st Int'l Sch. on Spintronics and Quantum Info. Tech., May 13-15, 2001 (Maui, HI, USA).

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