Transcript SPINTRONICS Prepared By :

SPINTRONICS
Prepared By :
The Future Belongs To Spintronics
OUTLINE
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Why Spintronics?
What is Spintronics?
Principle
Fabrication & Working of spin devices
Electronics Vs. Spintronics
Applications
Conclusion
Why Spintronics?
Moore’s Law:
No. of Transistor doubles in every 18 months
Complexity:
Complex Chip Design & Power Loss
Motivation:
Spintronics-Information is carried not by
electron charge but by it’s spin.
What is Spintronics?
Spintronics is a blend of electronics with
spin.
It refers to the study of the role played by
the electron spin in solid state physics and
possible devices that specifically exploits
spin properties of electrons instead of it’s
charge.
It promises new logic devices which
enhances functionality, high speed and
reduced power consumption.
Principle
Spintronics is based on the spin of electrons
rather than its charge.
Every electron exist in one of the two statesspin-up and spin-down, with spins either
positive half or negative half.
In other words, electrons can rotate either clock
wise or anti-clockwise around its own axis with
constant frequency.
The two possible spin states represent ‘0’ and ‘1’
in logical operations.
Principle
Spin is a characteristic that makes an electron a
tiny magnet with north and south poles.
The orientation of north-south axis depends on
the particle’s axis of spin.
In ordinary materials, the up magnetic
moments cancel the down magnetic moment
so no surplus moment piles up.
Ferro-magnetic materials like iron, cobalt and
nickel is needed for designing of spin
electronic devices.
Principle
These have tiny regions called domains in
which an excess of electrons have spins with
axis pointing either up or down.
The domains are randomly scattered and
evenly divided between majority-up and
majority-down.
But, an externally applied magnetic field will
line up the domains in the direction of the
field. This results in a permanent magnet.
Principle
When a pool of spin-polarized electrons is put
in a magnetic field, precession occurs.
The frequency and direction of rotation
depends on the strength of magnetic field and
characteristics of the material.
Thus, if a voltage pushes an electron out of
gallium arsenide into zinc selenide, the
electron precession characteristics change.
However, if a higher voltage pushes the
electron sharply into zinc selenide, the
electron precession characteristics don’t
change.
Principle
N-type materials rely on electrons to carry
current where as P-type materials rely on
holes.
As the materials are of two different carrier
types, an electric field is formed around their
junction.
This field is strong enough to pull a pool of
spin
coherent
electrons
from
GaAs
immediately into ZnSe, where coherence
persist for 100 of nanoseconds.
Thus, spin can be moved from one kind of
semiconductor to another without the need for
external electric fields.
Fabrication
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Spintronics devices involves two different
approaches for designing & manufacturing.
Perfecting the existing giant magneto resistance,
GMR based technology by developing new
materials with larger spin polarization.
Finding the novel ways of both generation and
utilization of spin polarized current.
The later one is a effective method.
Working
All spintronic devices acts according to the
simple scheme: The information is stored
(written) into spins as a particular spin
orientation (up or down).
The spins, being attached to mobile electrons,
carry information along a wire and the
information is read at a terminal.
Spin orientation of conduction electrons
survives for relatively long time (nanoseconds,
compared to tens of femtoseconds during
which electron moment decays) which makes
spintronic device useful for memory storage
and magnetic sensor applications.
Working
These are used for quantum computing where
electron spin will represent a bit (called ‘qubit’)
of information.
When electron spins are alligned, this creates a
large scale net magnetic moment.
The basic GMR device is a 3 layer sandwich of
magnetic metal (such as cobalt) with a nonmagnetic metal filling (such as silver).
A current passes through the layers consisting
of spin up and spin down electrons.
The electrons oriented in the same direction as the electron spin in the
magnetic layer pass through quite easily while those oriented in the opposite
direction are scattered.
If orientation of one of the magnetic layers is changed by the presence of a
magnetic field, the device will act as a filter or a spin valve letting through
more electrons when spin orientation in the two layers are the same and
fewer electrons when spin orientation are oppositely alligned.
The electrical resistance of the device can therefore be changed
dramatically.
The above diagram depicts the nature of the spin valve when the two
layers are oppositely alligned.
Electronics vs. Sprintronics
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One of the main advantage of spintronics over
electronics is the magnets tend to stay
magnetize which is sparking in the industry an
interest
for
replacing
computer’s
semiconductor based components with
magnetic ones, starting with the RAM.
With an all-magnetic RAM, it is now possible
to have a computer that retains all the
information put into it. Most importantly,
there will be no ‘boot-up’ waiting period when
power is turned on.
Electronics vs. Sprintronics
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Another promising feature of spintronics
is that it doesn’t require the use of
unique and specialized semiconductor,
there by allowing it to work with
common metals like Cu, Al, Ag.
Spintronics will use less power than
conventional electronics, because the
energy needed to change spin is a minute
fraction of what is needed to push charge
around.
Electronics vs. Sprintronics
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Another advantage includes Nonvolatility: Spins don’t change when
power is turned off.
The peculiar nature of spin and quantum
theory describes it point to other
wonderful possibility like various logic
gates whose function can be changed
billion times per second.
Application
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The Magnetic version of RAM used in
computer is nonvolatile.
Other advantages of MRAM’s include small
size, lower cost, faster speed and less power
consumption, robust in extreme condition
such as high temperature, high level
radiation and interference.
Applications
Magnetic RAM
Applications
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GMR sensors find a wide range of applications:
Fast and accurate position and motion sensing
of mechanical components in precision
engineering and robotics.
Missile Guidance
Position and motion sensing in computer video
games.
Key Hole Surgery and post operative care.
Automotive sensors for fuel handling system,
speed control and navigation etc.
Applications
Spin Valve Transistors:
It is based on magneto
resistance, found in multi
layers (Co-Cu-Co) forming
the base region.
The
collector
current
becomes
strongly
field
dependent, the extreme
magneto sensitivity makes
the transistor, an interesting
device for high technology
hard disks and magnetic
RAMs.
Conclusion
With lack of dissipation, spintronics may be
the best mechanism for creating ever-smaller
devices. The potential market is enormous, In
maybe a 10-year timeframe, spintronics will
be on par with electronics. That's why there's
a huge race going on around the world In
exploring Spintronics.
The Future Belongs To Spintronics
Any Queries…?
The Future Belongs To Spintronics
Thank you all