1. Department of Electronics
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
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).

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

8. 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 ~ rpm.

9. 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

10. HDD Operation 10

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

12. 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).

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. * 13

14. Gap between HDD and DRAM
A gap between data storage and operation : * 14

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 * * 15

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 16

17. HDD vs Flash Memory Demand for flash memories :
Price of flash memories : * 17

18. 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).

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 :* **

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)
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

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). 22

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

24. 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).

25. 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).

26. 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 , 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
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).

29. 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).

30. 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).