The magnetically sensitive transistor (also known as the spin transistor or spintronic transistor—named for spintronics, the technology which this development spawned), originally proposed in 1990 and currently still being developed, is an improved design on the common transistor invented in the 1940s. The spin transistor comes about as a result of research on the ability of electrons (and other fermions) to naturally exhibit one of two (and only two) states of spin: known as "spin up" and "spin down". Unlike its namesake predecessor, which operates on an electric current, spin transistors operate on electrons on a more fundamental level; it is essentially the application of electrons set in particular states of spin to store information.

1. SpinFET
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2. Need of Nanostructure device




Miniaturization Problems
Power dissipation
Short channel effects
Quantum mechanical
effects
 ballistic
 tunneling
Spin FET
 Spin of a electron S = ħσ/2
 Magnetic moment of a electron µspin = -gµBS/ ħ
σ = Pauli spin operator
µB = Bohr magnetron (eħ/2m)
http://www.nims.go.jp/apfim/SpinFET.html
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3. Spin-Orbit interaction
Heterojunction:
Atomic case
Enucleus
ˆ
Ze r

4 0 r 2
AlGaAs
j  Zev
InGaAs
 In analogy with the atomic
case Rashba S-O term
 In Electron rest frame
Amperes' law
B
0 j  r
4 r 2
E
Beff  0 0 (v  Enucleus )
S O    spin Beff 
H S O
g B S
(v  E )
2
hc
g  B

( p  V )
2
2mc
  ,k  x   ,k 
k y
k
  ,k  y   ,k 
  ,k  z   ,k  0
EE733 : SpinFET
kx
k
dV
ˆ
V  z
g B dz
dV
H S O 
[ ( p  z
)]
2
2mc
dz
g B
dV
H S O 
[z
(  p)]
2
2mc
dz

H S O 
[ z (  p)]
h
1

2
2
H
( px  p y )  ( x p y   y px )
2m
h
3

4. Giant magnetoresistance
(GMR)
RA: Resistance in the antiparallel configuration
RP: Resistance in the parallel configuration
http://www.aist.go.jp/aist_e/latest_research/2004/20041124/20041124.html
http://www.nims.go.jp/apfim/halfmetal.html
http://www.directvacuum.com/spin.asp
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5. Origin of GMR
 Mott Model
 Different resistivities
 Scattering is :
Parallel
Antiparallel
 Strong for electrons with
spin antiparallel to the
magnetization direction
 Weak for electrons with
spin parallel to the
magnetization direction
H. Ehrenreich and F. Spaepen, Academic Press, 2001, Vol. 56 pp.113-237
http://physics.unl.edu/tsymbal/reference/giant_magnetoresistance/origin_of_gmr.shtml
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6. SpinFET : Structure &
Working
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7. Electron spin
photon polarization
Supriyo Datta & Biswajit Das, Electronic analog of the eiectro-optic modulator, APL ,1989
http://nanohub.org/resources/11128
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8. Structure & Working of spinFET
=
Supriyo Datta & Biswajit Das, Electronic analog of the eiectro-optic modulator, APL ,1989
Satoshi Sugahara and Junsaku Nitta, Spin-Transistor Electronics: An Overview and Outlook, 2010
http://nanohub.org/resources/11128
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9. Spin Injection
 Source(polarizer) and drain(analyzer)
ferromagnetic material(Fe).
made
of
 Conditions with the polarizer (source) and analyzer
(drain) magnetizations parallel or antiparallel, resulting
in relatively high or low spin-dependent voltages at the
detector.
 Conductance(G) = 𝑞2 𝐷/𝑡.
Supriyo Datta & Biswajit Das, Electronic analog of the eiectro-optic modulator, APL ,1989
Satoshi Sugahara and Junsaku Nitta, Spin-Transistor Electronics: An Overview and Outlook, 2010
http://nanohub.org/resources/11128
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10. Channel Requirements
 2DEGs in narrow band gap semiconductor
 Ballistic tranport
 Avoid spin relaxation[1]
 Elliot Yafet
[2]
 D'yakonov-Perl
 Bir-Aronov-Pikus
[1] J. Fabian and S. Das Sarma, Spin relaxation of conduction electrons, 1993
[2] Satoshi Sugahara and Junsaku Nitta, Spin-Transistor Electronics: An Overview and Outlook, 2010
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11. Electrostatic control of spin
 Aharonov – Bohm
Experiment [1]
Conductance
[2]
variation
Phase difference in the
 Applied potential controls
the polarization of the
electron
wave vector
𝟐 𝒎∗ 𝜼𝒍
∆𝜽 =
ћ𝟐
[1] J. Nitta, F. E. Meijer, and H. Takayanagi, Spin-interference device, 1999
[2] Satoshi Sugahara and Junsaku Nitta, Spin-Transistor Electronics: An Overview and Outlook, 2010
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12. Gate control of the channel
Satoshi Sugahara and Junsaku Nitta, Spin-Transistor Electronics: An Overview and Outlook, 2010
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13. Non-ballistic SpinFET
Scattering tolerent
Dresselhaus spin-orbit
coupling
Making both the
coefficients equal
[1]
J. Schliemann, J. C. Egues, and D. Loss, Nonballistic spin-field-effect transistor, 2003
[1] Satoshi Sugahara and Junsaku Nitta, Spin-Transistor Electronics: An Overview and Outlook, 2010
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14. SpinFET improvemts
 Improvements
[1]
 Holes as carriers
 Strain engineering to shift the hole subbands
 Modified device structure
 Gate control hinderance [2]
 Fano resonance
 Ramsauer resonance
 Dual gate as an option
[1] D. M. Gvozdie, U. Ekenberg, and I. Thylen, Comparison of performance of spin transistors with conventional transistors, 2005
[2] J. Wan, M. Cahay, and S. Bandyopadhyay, Proposal for a dual-gate spin field effect transistor: A device with very small
switching voltage and a large ON to OFF conductance ratio, 2008
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15. Spintronics so far..
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16. Giant Magneto-Resistance (GMR)
 Discovered by Albert Fert
and Peter Gruenberg
independently in 1988.
 IBM researcher Stuart Parkin
created hard disk read
heads, which tremendously
improved data storage and
speed.
 Nobel prize for GMR in
2007.
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17. Memory Applications
MRAM
Non-volatile
Lower power consumption
than a DRAM
Write power only slightly
greater than read.
Slightly lower performance
than SRAM
Viewed as a universal
memory element.
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18. SpinFET based Memory
 Depending on the relative direction of magnetization of
Free electrode relative to the Fixed magnetization
electrode the channel will provide a low/high resistance .
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19. Logic Applications
AND Logic
NAND Logic
Magnetoelectric Spin-FET for Memory, Logic,and Amplifier Applications, S. G. Tan et al., 2005
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20. Things that gives hope..
 A family of silicon-based semiconductors that exhibit
magnetic properties has been discovered in 2004.
 A team of Princeton scientists has turned semiconductors into
magnets by the precise placement of metal atoms within a
material from which chips are made in 2006.
 Scientists prove the existence of a spin battery.
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21. Thank You
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