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  (TN) : Néel temperature Antiferromagnetism AFM PM Ferromagnetism  (TC) : Curie temperature Ferrimagnetism FM PM

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

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

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

Discovery of Giant Magnetoresistance Giant magnetoresistance ( GMR ) : [ 3 nm Fe / 0.9 nm Cr ]  60 * MR H = 0 Spin-valve “OFF” MR Ratio H = Saturation 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).

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

Do NOT Try This at Home ! Open a metal frame of a HDD … Platter Magnet Arm ・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.

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

HDD Operation 10

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

Aerial Density Increase by GMR Introduction Aerial density growth of hard disk drives : Superparamagnetic limit 60 % / yr. with GMR heads 30 % / yr. with AMR heads * D. A. Thompson et al., IBM J. Res. Develop 44, 311 (2000).

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/ 13

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

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/ 15

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 16

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

Advantages of MRAM MRAM FeRAM FLASH DRAM SRAM 1'' HDD Non-volatality   Read time 300 ns (GMR) <60 ns (TMR) 100 ~ 200 ns 50 ns   ~ 10 ms Write time < 10 ns ~100 ns ~ 10 s Repetition > 10 15 10 9 ~10 12 10 5 Cell density 6 ~ 12 F 2 8 F 2 4 F 2 △  Chip capacity > 1 Gb < 10 Mb Power < 10 mW > 10 mW > 1 W Soft error hardness Process cost RT process HT process Lower bit cost Lowest bit cost * After K. Inomata, J. Magn. Soc. Jpn. 23, 1826 (1999).

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).

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

Improved MRAM Operation Required writing currents for several techniques dependent upon cell size : Ampère-field-induced magnetisation reversal with a ferromagnetic overlayer (Current technology) Current-induced magnetisation reversal JC ~ 10 7 A / cm 2 (Current technology) Ampère-field-induced magnetisation reversal without a ferromagnetic overlayer (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). 21

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). 22

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

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

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

Improved Tunnel Barriers Conventional amorphous barriers : * 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 Epitaxial (oriented) barriers : * 1 2 , 5 * After S. Yuasa et al., 28th Annual Conference on Magnetics, Sep. 21-24, 2004 (Okinawa, Japan).

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

Spin-Polarised Three-Terminal Devices Gate Voltage Input Output FM / SC hybrid Structures Magnetic tunnel junctions (MTJ) All metal and spin valve structures Interface Ohmic / Schottky barriers Tunnel barriers Ohmic (no barrier) Spin carriers SC Non-magnetic metals Device applications FM / 2DEG Schottky diodes Spin FET Spin LED Spin RTD MOS junctions Coulomb blockade structures SP-STM Supercond. point contacts Johnson transistors Spin valve transistors * After M. Johnson, IEEE Spectrum 37, 33 (2000).

Major Spin-Polarised Three-Terminal Devices Spin FET Spin LED Spin RTD Coulomb blockade Input Spin-polarised electrons / holes electrons Source Ferromagnets (FM) Dilute magnetic semiconductors (DMS) Double tunnel barriers Gate Bias voltage Drain Quantum wells (QW) Output Electrical signals - Circularly polarised electroluminescence (EL) Electrical signals Notes Low temperature High magnetic field Refs. S. Datta and B. Das, Appl. Phys. Lett. 56, 665 (1990). Y. Ohno et al., Nature 402, 790 (1999). T. Gruber et al., Appl. Phys. Lett. 78, 1101 (2001). K. Yakushiji et al., Appl. Phys. Lett. 78, 515 (2001).

Spin Valve / Magnetic Tunnel Transistors Spin valve transistor : * Magnetic tunnel 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., Science 281, 407 (1998); † S. S. P. Parkin, 1st Int'l Sch. on Spintronics and Quantum Info. Tech., May 13-15, 2001 (Maui, HI, USA).