In our conventional electronic devices we use semi conducting materials for logical operation and magnetic materials for storage, but spintronics uses magnetic materials for both purposes. These spintronic devices are more versatile and faster than the present one. One such device is Spin Valve Transistors (SVT). Spin valve transistor is different from conventional transistor. In this for conduction we use spin polarization of electrons. Only electrons with correct spin polarization can travel successfully through the device. These transistors are used in data storage, signal processing, automation and robotics with less power consumption and results in less heat. This also finds its application in Quantum computing, in which we use Qubits instead of bits.

1. SPIN VALVE
TRANSISTOR
SUBMITED TO SUBMITTED BY SEMINAR GUIDE
Er. AMIT KATIYAR EESHAN MISHRA Er. AJEET KUMAR SRIVASTAVA
Er. ROLI NIGAM
(SEMINAR IN CHARGE)

2. WHAT IS
SPINTRONICS?
Spintronics also known as magneto electronics,
manipulates the electron spin and resulting magnetic
moment, to achieve improved functionalities e.g.
Spin transistors, memories etc.

3. The charge is the origin
of electricity, and its
flow leads to an electric
(charge) current.
SPIN CURRENT
On the other hand, the
spin gives rise to
magnetism and its
flow is called spin
current.
Spin current can also
be generated by
producing a
temperature gradient in
a magnetic insulator.
By combining general
relativity and quantum
mechanics. This finding
opens up opportunities
for the direct conversion
of quantum mechanical
rotation into its classical
counterpart, which can
lead to inventions of
Nano scale motors.
The thermally induced
spin current is
converted to an electric
current via the inverse
spin Hall effect in an
attached metal.

4. Using magnetization dynamics induced
by ferromagnetic resonance
researchers have succeeded in
injecting spin currents into
semiconductors with a very high
efficiency (103 times larger than before)

7. HOW IT ALL BEGAN??
Spintronics came into light by the advent of Giant
Magneto Resistance (GMR) in 1988.
In 1988, the giant magneto resistance (GMR) effect
was discovered in multilayer structures that contain
layers of ferromagnetic metals separated by a thin
spacer of normal metal.
The Nobel Prize for physics in 2007 was awarded to
the discoverers of Giant Magneto-Resistance, or
GMR for short.

8. GIANT MAGNETO RESISTANCE
The resistance of such structures depends
greatly on the relative magnetic orientation of
neighbouring magnetic layers, making it
attractive for application in highly sensitive
magnetic field sensors.
PARALLEL CURRENT
• Current runs parallel between the
ferromagnetic layers.
• Most commonly used in magnetic read
heads.
• Has shown 200% resistance difference
between zero point and antiparallel states.
PERPENDICULAR CURRENT
One FM layer as spin polarizer and other as detector.
Has shown 70% resistance difference between zero point
and antiparallel states.
Basis for Tunneling Magneto Resistance.

9. SOME MORE SPINTRONIC DEVICES
Tunnel Magneto Resistance (TMR)
Magnetic Tunnel Junctions (MTJ)
Spin Valve
Spin Transfer Torque (STT)

10. NEED TO MERGE SPINTRONICS WITH
SEMICONDUCTOR ELECTRONICS??
Semiconductors allow
• Precise tuning of carrier
concentrations
• Band gap engineering, and,
interestingly,
• Exhibit extremely long electron
spin lifetimes.

11. HOW SEMICONDUCTOR CAN BE COMBINED WITH
FERROMAGNETIC MATERIALS ?

12. 1. HYBRID SYSTEM
The most
straightforward
approach is the
one employed in
MRAM
An array of
magnetic
memory
elements is
placed on top of
semiconductor
wafer containing
transistors and
other circuitry
required to drive
the memory.
The drawback
lies in the fact
that it does not
utilises the
unique property
of
semiconductor
in manipulating
spin.

13. 2. MAGNETIC
SEMICONDUCTORS
The most intimate form of
integration is to put
magnetic properties into
semiconductor materials,
thus creating
ferromagnetic
semiconductors.
Such materials can be
obtained by doping
with a certain amount
of magnetic atoms, as
in case of GaMnAs.

14. 3. HYBRID DEVICES
The hunt is now on for compounds that exhibit
both semiconducting and ferromagnetic properties
at temperatures well above room temperature.
As seen above clearly magnetic film layer is
grown over silicon substrate and a silicon layer
above it.

15. Two main categories will
be distinguished, based
on whether the control
and manipulation of the
spins occurs in the --
semiconductor
material
or
ferromagnetic
material

16. In the first category, electron spins that originate from a
ferromagnetic source material are injected into a semiconductor, in
which they are transported and manipulated, followed by some
means of spin detection at the ‘other end’ of the device.
The implementation into working devices that operate at room
temperature remains to be demonstrated.
For the second class of hybrid devices, where a device concept
has been successfully demonstrated by Monsma et al with the
introduction of the spin-valve transistor (SVT) in 1995, and
The subsequent observation of huge magnetic response at room
temperature a few years later.

17. WHAT IS SPIN VALVE TRANSISTOR?
The SVT was introduced in 1995 and is the first working hybrid
device in which Ferro magnets and semiconductors have been
closely integrated, and both materials are essential in controlling
the electrical transport through the device.
Spin transistors would allow control of the spin current in the
same manner that conventional transistors can switch charge
currents.
Consists of a silicon emitter, a magnetic multi-layer as the base
and a silicon collector.
SVT is a hot electron device.

18. DEVICE CHARACTERISTICS
Figure 2. Basic layout of the SVT, showing the three terminal
arrangement with semiconductor emitter (top), semiconductor
collector (bottom), and the metallic base comprising two
ferromagnetic thin layers separated by normal metals (middle).

19. The three-terminal device has the typical
emitter/base/collector structure of a (bipolar) transistor,
but is different in that the base region is metallic and
contains at least two magnetic layers separated by a
normal metal spacer.
The two magnetic layers act as polarizer and analyser
of electron spins, such that the relative orientation of
the magnetization of the two layers determines the
transmission of the base.
Spin dependence of the transport is in the
ferromagnetic materials, the semiconductors are used
to create energy barriers in the electron’s potential
landscape that are essential to the operation of the
device.

20. The resulting salient feature of the SVT is that
the collector current depends on the magnetic
state of the base.
They succeeded in the reproducible fabrication
of SVTs that exhibit magnetocurrent effects up
to 400% at room temperature, and in small
magnetic fields of only a few Oe.
the SVT is based on the spin-dependent
transport of non-equilibrium, so-called hot
electrons, rather than Fermi electrons.

22. SVT uses silicon as the semiconductor for the emitter and collector,
and has a metallic base that contains a Ni80Fe20/Au/Co spin valve.
At the interfaces between the metal base and the semiconductors,
energy barriers (Schottky barriers) are formed.
These energy barriers prevent electrons with the Fermi energy from
travelling through the structure.

23. At the interfaces between the metal base and the
semiconductors, energy barriers (Schottky barriers) are
formed.
These energy barriers prevent electrons with the Fermi
energy from travelling through the structure.
High quality Schottky barrier with good rectifying
behaviour and thermionic emission dominating, low
doped Si (1–10cm) is used, and thin layers of, e.g. Pt and
Au are incorporated at the emitter and collector side.

24. APPLICATIONS
Spin transistors have huge potential for incorporation in stable, high sensitivity magnetic field
sensors for automotive, robotic, mechanical engg. & data storage applications.
This may also be used as Magnetically Controlled Parametric Amplifiers & Mixers, as
magnetic signal processors, for control of brush less DC motors & as Magnetic Logic elements.
In log applications they have the advantage over conventional semiconductor chips that they do not
require power to maintain their memory state.
Quantum Computer, a new trend in computing. Here we use Qubits instead of bits. Qubit also
represents only 1& 0 but here they show superposition these classical states. But it is in pioneering
stage.
There are major efforts ongoing at Honeywell, IBM, Motorola in developing RAM based on spin
valves and metal tunnel junctions such devices called MRAM have demonstrated faster speed, high
density low power consumption, non-volatility and radiation harness they are promising
replacements for the Semi Conducting RAM currently used.

25. ADVANTAGES OF SVT (SPIN VALVE TRANSISTOR)
Traditional transistors use on & off charge currents to create bits – the
binary 0 & 1 of Computer information. Quantum spin field effect transistor
will use up & down spin states to generate the same binary data.
A currently logic is usually carried out using conventional electrons, while
spin is used for memory. Spintronics will combine both.
In most Semi Conducting transistors the relative proportion of the up &
down carries types are equal. If Ferro Magnetic material is used as the
carrier source then the ratio can be deliberately skewed in one direction.
Amplification and / or switching properties of the Device can be controlled
by the external magnetic field applied to the device.
One of the problems of charge current electrons is that we pack more
devices together, the chip heats up. Spin current releases heat but it is
rather less.

26. LIMITATIONS
Controlling spin for long distances.
Difficult to INJECT and MEASURE spin.
Interference of fields with nearest
elements.
Control of spin in silicon is difficult.

27. CONCLUSION
Spinvalve transistor is more versatile and more robust but
it needs further fabrication methods to improve magnetic
sensitivity of collector current.
The greatest hurdle for spintronic engineers may be
controlling all that spin.
The key question will be whether any potential benefit of
such technology will be worth the production cost.
Spin valve transistors and other spin devices will become
affordable by using common metals.