51366050 Spin Valve Transistor.ppt
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Transcript of 51366050 Spin Valve Transistor.ppt
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A step towards quantum computers
By Shashank Shetty
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Index: Introduction
Construction
Working Magnetic sensitivity
Temperature effects
Applications
Advantages
Conclusion
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Introduction:
Its a spintronics device.
Conduction is due to spin polarization of
electronics.
Two experiments in 1920s suggested spin as
an additional property of an electron:
1. Closely spaced splitting of hydrogen
spectralines
2. Stern-Gerlach experiment
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The starting material for both emitter andcollector is a 380um, 5-10Ocm, n-si (100)wafer.
Wafer is dry oxidised to anneal the implantand to form a SIO2 layer.
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The hydrophobic surface of emitter iscontacted to the multilayer surface, forming abond through spontaneous adhesion.
Base multilayer is rf sputtered through a lasercut metal shadow mask on the collector
surface.
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Working
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Working(contd..) The collector barrier height about 0.7eV while the
emitter barrier height is 0.6eV.
After accelerating the electrons from emitter theyconstitute a hot Ballistic electrons in the base.
Current gain is given by,
o = (Jc Jleak ) / Je = c e qm e-w/y
where,e = emitter efficiency
c = collector efficiency
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Working(contd..) qm = quantum mechanical transmission
W = base width
= the hot electron mean free path e-w/= the probability of transmission of the hot
electrons through the base
Jc =the total collector current Jleak = the collector leakage current
Je=the injected emitter current
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Working(contd..) Collector current is given by
Jc = Jc+ + Jc- = Jc c e qm [ Pi+ + Pi-] + Jleak
i i The sum of the transmission probability factors for the
two spin channels can be written as
= [ Pi+ + Pi- ] = e-wcu / cu [e-wco / co
i i
e-wF/N / F/N + e-wco / co e-wF/N / F/N]
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Working(contd..)At the coercive field, this quantity becomes.
= [ Pi+ + Pi- ] AP = e-wcu / cu [2e-wco /2co
i ie-wF/N / 2F/N e-wco / 2co e-wF/N / 2F/N]
Wco=the sum of all Co layer widths
Wcu=the total Cu thickness.
exp. (-WF/N /F/N()), a spin dependent factorwhich takes into account the spin dependentscattering at the interfaces.
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MAGNETIC SENSITIVITY
The leakage current is quiet large (30A) and
exceeds the magneto current for an injection
current of 100mA because of low barrier
height and large collector area.
To reduce the leakage current to acceptible
value, Magneto current measurements havebeen performed at 77 K.
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MAGNETIC SENSITIVITY(CONTD..)
Magnetic sensitivity of collector current at different
temperatures
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Temperature effects
The collector current across the spinvalve changes its relative orientation
of magnetic movements at finite
temperature. The parallel collector current is
increasing up to 200 K and decreasing
after that, while anti-parallel collectorcurrent is increasing up to room
temperature.
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Temperature effects(contd..)
Two different mechanisms aresuggested. One of them is spatial
distribution of Schottky barrier diode.
This may explain the behaviors of bothparallel and antiparallel collector
current upto 200K.
Spin mixing is spin flip process bythermal spin wave emission or
absorption at finite temperatures.
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Used as stable, high sensitivity magnetic
field sensorsforautomotive, robotic,mechanical engg. & data store
application.
Used as Magnetically Controlled
Parametric Amplifier & Mixer.
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Used as Magnetic Signal Processor, for
control of brushless DC motors & as
Magnetic logic elements.
In log applications they have the
advantage over conventional
semiconductor chips.
Used in Quantum computing.
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Advantages
Traditional transistors use on & off charge currentsto create bits. Quantum spin field effect transistorwill use up & down spin states to generate the same
binary data
A currently logic is usually carried out usingconventional electrons, while spin is used for
memory. Spintronics will combine both.
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Advantages(contd..)
In most Semi Conducting transistors the relativeproportion of the up & down carries types areequal. If Ferro Magnetic material is used as the
carrier source then the ratio can be deliberatelyskewed in one direction.
Amplification and / or switching properties of theDevice can be controlled by the external magnetic
field applied to the device. Spin current releases heat but it is rather less.
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Spin valve transistor is more versatile andmore robust.
Implementing it on a whole circuit will requiresome clever ideas as controlling the spinremains the greatest hurdle.
However the key question will be whether anypotential benefit of such technology will be
worth the production cost.
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QUESTIONS??
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THANK YOU