Nanoelectronics 12. Atsufumi Hirohata Department of Electronics. Quick Review over the Last Lecture

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1 Nanoelectronics 12 Atsufumi Hirohata Department of Electronics 09:00 Tuesday, 20/February/2018 (P/T 005) Quick Review over the Last Lecture Origin of magnetism : ( Circular current ) is equivalent to a ( magnetic moment ). Dipole moment arrangement : Paramagnetism Q (T N ) : Néel temperature Antiferromagnetism AFM PM Ferromagnetism Ferrimagnetism FM Q (T C ) : Curie temperature PM

2 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

3 Recent Progress in Magnetoelectronics I - Giant Magnetoresistance 1995 Photoexcitation 1999 Spin detection 1975 TMR SP-STM % TMR 1997 Double tunnel junction Ultra high density HDD GMR 1981 Giant g DMS 1990 Spin FET 1989 Carrier-induced FM GMR head MRAM 1996 Photo-induced FM 1994 Optical isolator Fast & high density nonvolatile memory Spin-Dependent 3-terminal device 2000 RT FM 1999 Spin injection Spin LED * After K. Inomata, J. Magn. Soc. Jpn. 23, 1826 (1999). Giant magnetoresistance ( GMR ) : Discovery of Giant Magnetoresistance [ 3 nm Fe / 0.9 nm Cr ] 60 * MR H = 0 Spin-valve MR Ratio H = Saturation Spin-valve 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).

4 How Can We Find a Hard Disc Drive? Open your computer This is a HDD! Open a metal frame of a HDD Do NOT Try This at Home! Magnet Arm Platter Arm is operated by a linear motor with a very strong permanent magnet. - Arm moves ~ 100 times/sec. - Platter records data. - Platter rotates 5400 ~ rpm.

5 Where Can We Find a Hard Disc Drive? Hard disc recorder Video game PC GPS navigation Digital camera Video camera Data storage PDA Most popular recording media now : mp3 player Mobile phone HDD Operation

6 HDD Writing / Reading Operation HDD writing operation : HDD reading operation : Aerial Density Increase by GMR Introduction Aerial density growth of hard disk drives : limit % / yr. with heads % / yr. with heads * D. A. Thompson et al., IBM J. Res. Develop 44, 311 (2000).

7 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. * Gap between HDD and DRAM A gap between data storage and operation : *

8 Flash Memory In 1980, Fujio Masuoka invented a NOR-type flash memory : ü 1 byte high-speed read-out û Low writing speed û Difficult to integrate û Flash erase for a unit block ( 1 ~ 10 kbyte ) only! In 1986, Fujio Masuoka invented a NAND-type flash memory : û No 1 byte high-speed read-out ü High writing speed ü Ideal for integration * * Solid State Drive with Flash Memory Solid state drive (SSD) started to replace HDD : puresi introduced TB SDD in 2009 : ü Data transfer speed at 300 MB/s û 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

9 HDD vs Flash Memory Demand for flash memories : Price of flash memories : * 3D Flash Memory

10 Advantages of MRAM MRAM FeRAM FLASH DRAM SRAM 1'' HDD Nonvolatality Read time 300 ns (GMR) <60 ns (TMR) 100 ~ 200 ns 50 ns ~ 10 ms Write time < 10 ns ~100 ns ~ 10 µs ~ 10 ms Repetition > ~ Cell density 6 ~ 12 F 2 8 F 2 4 F 2 ¾ Chip capacity > 1 Gb < 10 Mb > 1 Gb ¾ 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, 1 st Int'l Sch. on Spintronics and Quantum Info. Tech., May 13-15, 201 (Maui, HI, USA).

11 MRAM Demonstration Freescale (now EverSpin Technologies) 4 Mbit MRAM : * ** Improved MRAM Operation Required writing currents for several techniques dependent upon cell size : Write current (ma) Current-induced magnetisation reversal J C ~ 10 7 A / cm 2 (Current technology) 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 J C ~ 10 6 A / cm 2 Current-induced magnetisation reversal J C ~ A / cm 2 MRAM cell size (µm) * S. Nakamura, Y. Saito and H. Morise, Toshiba Rev. 61, 40 (2006).

12 Current-Induced Magnetisation Reversal Anti-parallel (AP) «parallel (P) reversal in a GMR / TMR junction : * 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 ** J. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996); L. Berger, Phys. Rev. B 54, 9353 (1996). Recent Progress in Magnetoelectronics II - Tunnel Magnetoresistance 1995 Photoexcitation 1999 Spin detection 1975 TMR GMR 1981 Giant g DMS 1990 Spin FET 1989 Carrier-induced FM SP-STM % TMR 1997 Double tunnel junction GMR head MRAM 1996 Photo-induced FM 1994 Optical isolator Ultra high density HDD Fast & high density nonvolatile memory Spin-Dependent 3-terminal device 2000 RT FM 1999 Spin injection Spin LED * After K. Inomata, J. Magn. Soc. Jpn. 23, 1826 (1999).

13 Jullière's model : FM / insulator / FM junctions * E c Spin-Dependent Electron Tunneling Incident Bloch wave Transmitted Bloch wave E 1 = µ 1 E 1 = 0 ev E 2 = µ 2 Atom 1 Barrier Atom 2 E v E 2 = 0 r (r ) FM1 Oxide Barrier FM2 3d a a 1 a a 2 a a a 2 a 2 4p E F 4s r (a) (b) * M. Jullière., Phys. Rep. 54A, 225 (1975). Recent progress in TMR ratios : TMR for Device Applications > 400 % TMR ratio has been achieved! > Gbit MRAM can be realised. NOT following Jullière's model : ** TMR = 2P 1 P 2 / ( 1 - P 1 P 2 ) * M. Jullière., Phys. Rep. 54A, 225 (1975). ** S. S. P. Parkin, 1 st Int'l Sch. on Spintronics and Quantum Info. Tech., May 13-15, 2001 (Maui, HI, USA).

14 Conventional amorphous barriers : * Improved Tunnel Barriers D 1 D 2, D 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 : * D 1 D 2, D 5 * After S. Yuasa et al., 28th Annual Conference on Magnetics, Sep , 2004 (Okinawa, Japan). Latest MRAM * News from EverSpin, IBM and Toshiba.

15 Recent Progress in Spintronics 1995 Photoexcitation 1999 Spin detection 1975 TMR GMR 1981 Giant g DMS 1990 Spin FET 1989 Carrier-induced FM SP-STM % TMR 1997 Double tunnel junction GMR head MRAM 1996 Photo-induced FM 1994 Optical isolator Ultra high density HDD Fast & high density nonvolatile memory Spin-Dependent 3-terminal device 2000 RT FM 1999 Spin injection Spin LED * After K. Inomata, J. Magn. Soc. Jpn. 23, 1826 (1999). Spin-Polarised Three-Terminal Devices Gate Voltage Control Input Output Source Drain Interface FM / SC hybrid Structures Ohmic / Schottky barriers Magnetic tunnel junctions (MTJ) Tunnel barriers All metal and spin valve structures Ohmic (no barrier) Spin carriers SC Tunnel barriers 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 Spin RTD Johnson transistors Spin valve transistors * After M. Johnson, IEEE Spectrum 37, 33 (2000).

16 Major Spin-Polarised Three-Terminal Devices Spin FET Spin LED Spin RTD Coulomb blockade Input Spin-polarised electrons / holes Spin-polarised electrons / holes Spin-polarised electrons / holes Spin-polarised electrons Source Gate Bias voltage Bias voltage Bias voltage Bias voltage Drain Output Electrical signals - Spin-polarised electrons / holes Circularly polarised electroluminescence (EL) Circularly polarised electroluminescence (EL) Electrical signals Notes Low temperature High magnetic field Low temperature Low temperature 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, 1 st Int'l Sch. on Spintronics and Quantum Info. Tech., May 13-15, 2001 (Maui, HI, USA).