TECHNICAL SEMINAR ON

SPINTRONIC TECHNOLOGY

Submitted in Partial Fulfillment of the requirement For the award of degree of Bachelor of Technology

In

ELECTRONICS AND COMMUNICATION ENGINEERING

Submitted by

A. DIVYAJYOTHI 096L1A0405

Under the Esteemed coordinator of

D.V.RAJESHWAR RAJU

(Assistant Professor)

PRASAD ENGINEERING COLLEGE(Approved by AICTE and Affiliated to JNTU Hyderabad)

JANGAON, WARANGAL, 506167(AP)

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Certificate

This is to certify that the mini project report entitled SPINTRONIC TECHNOLOGY is

being submitted by A. DIVYAJYOTHI in partial fulfillment of the requirement for the award of

degree in Bachelor of Technology in Electronics and Communication Engineering during the

period 2009-2013. This is a record of students own work carried out by them under our

supervision and guidance.

The matter enclosed in this project report has not been submitted for the award of any

other Degree.

D.V.RAJESHWAR RAJU. B.SWAMY.

Coordinator Head of the Department

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ACKNOWLEDGEMENT

My special thanks to Mrs.D.RAMADEVI, Principal and management for

providing all the facilities required for completing this seminar.

We are very grateful to Mr.B.SWAMY, Head of the department, and

ELECTRONICS AND COMMUNICATION ENGINEERING for his inspiring guidance

and advice throughout the project.

We owe our deep depth of gratitude to our coordinator D.V.RAJESHWAR RAJU,

Assistant professor for his valuable guidance and constant encouragement at each

stage of this project work.

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ABSTRACTKeywords:(GMR)

“Spintronics” is an emergent NANO technology, which uses the spin of an electron

instead of or in addition to the charge of an electron. Electron spin has two states either “up” or

“down”. Aligning spins in material creates magnetism. Moreover, magnetic field affects the

passage of spin-up and spin-down electrons differently the paper starts with the detail description

of the fundamentals and properties of the spin of the electrons. It proceeds with a note on

magneto resistance, the development of Giant Magneto resistance (GMR) and devices like

Magneto Random Access Memory, which are the new version of the traditional RAMs. It

describe how this new version of RAMs which can revolutionize the memory industry. There is

also detailed explanation of the way, how this revolution can increase the data density in our

memory systems. It is followed by an account of new Spin Field Effect Transistors. It also

specifies the differences between electronic devices and spintronic devices. It also gives the

hurdles due to the presence of holes. This paper also discusses about a quantum computer, which

uses qubits rather than normal binary digits for computations. It also gives the hurdles due to the

presence of holes. Finally it ends with a note on why we should switch on this technology. Ran

road track and conveyor belts kept the Ford’s assemble line running. At that time, his method of

production was lauded and was considered most efficient. But that ford’s assembly plant, which

was only eulogized in his time, will look strange to those who were born and raised up in the

21st century. Because the machines in the next 50 years will get increasingly smaller – so small

that thousands of machines will fit into the full stop at the end of this line. This branch of

engineering which deals with things smaller than 100 nanometers is termed as Nanotechnology.

Eric Dexler first coined it in his book “engine of creation”.

In this paper we will discuss about a field of Nanotechnology, which is believed to

replace conventional electronics in the near future, i.e. “spintronics”.

Chapter-1

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INTRODUCTION

1.1 SPINTRONICS

Imagine a data storage device of the size of an atom working at a speed of light. Imagine

a microprocessor whose circuits could be changed on the fly. One minute is could be optimized

for data base access. The next for transaction processing and the next for scientific number

crunching. Finally, imagine a computer memory thousands of times denser and faster than

today’s memories.

The above-mentioned things can be made possible with the help of an exploding science

– “spintronics”. Spintronics is a NANO technology which deals with spin dependent properties

of an electron instead of or in addition to its charge dependent properties, Conventional

electronics devices rely on the transport of electric charge carries electrons. But there is other

dimension of an electron other than its charge and mass i.e. spins. This dimension can be

exploited to create a remarkable generation of spintronic devices. It is believed that in the near

future spintronics could be more revolutionary than any other thing that nanotechnology has

stirred up so far.

1.2 WHY IS IT GOING TO BE ONE OF THE RAPIDLY EMERGING

FIELDS?

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As there is rapid progress in the miniaturization of semiconductor electronic devices

leads to a chip features smaller than 100 nanometers in size, device engineers and physists are

inevitable faced with a looming presence of a quantum property of an electron known as spin,

which is closely related to magnetism. Devices that rely on an electron spin to perform their

functions from the foundations of spintronics. Information-processing technology has thus far

relied on purely charge based devices ranging from the now quantum, vaccume tube today’s

million transistor microchips. Those conventional electronic devices move electronic charges

around, ignoring the spin that tags along that side on each electron.

CHAPTER-2ELECTRON SPIN

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2.1 FUNDAMENTALS OF SPIN

1. In addition to their mass and electric charge, electrons have an intrinsic quantity of angular

momentum called spin, almost of if they were tiny spinning balls.

2. Associated with the spin is magnetic field like that of a tiny bar magnet lined up with the spin

axis.

3. Scientists represent the spin with a vector. For a sphere spinning “west to east”, the vector

points “north” or “up”. It points “down” for the opposite spin.

4. In a magnetic field, electrons with “spin up” and “spin down” have different energies.

5. In an ordinary electronic circuit the spins are oriented at random and have no effect on current

low.

6. Spintronic devices create spin-polarized currents and use the spin to control current flow.

Electrons like all fundamental particles have a property called spin, which can be oriented in one

direction, or the other called spin-up or spin-down. Magnetism is an intrinsic Physical property

associated with the spins. An intuitive notion of how an electron spins is suggested below.

Imagine a small electronically charged sphere spinning rapidly. The circulating charges

in the sphere amount to tiny loops of electric current which creates a magnetic field.. a spinning

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sphere in an external magnetic field changes its total energy according to how its spin vector is

aligned with the spin. In some ways, an electron is just like a spinning sphere of charge, an

electron has a quantity of angular momentum (spin) an associated magnetism. In an ambient

magnetic field and the spin changing this magnetic field can change orientation. Its energy is

dependent on how its spin vector is oriented. The bottom line is that the spin along with mass

and charge is defining characteristics of an electron,. In an ordinary electric current, the spin

points at random and plays no role in determining the resistance of a wire or the amplification of

a transistor circuit. Spintronic devices in contrast rely on the differences in the transport of spin-

up and spindown electrons.

CHAPTER-3GMR

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3.1 GIANT MAGNETO RESISTANCE

Magnetism is the integral part of the present day’s data storage techniques. Right from

the Gramophone disks to the hard disks of the super computer magnetism plays an important

role. Data is recorded and stored as tiny areas of magnetized iron or chromium oxide. To access

the information, a read head detects the minute changes in magnetic field as the disk spins

underneath it. In this way the read heads detect the data and sent it to the various succeeding

circuits. The magneto resistant devices can sense the changes in the magnetic field only to a

small extent, which is appropriate to the existing memory devices. When we reduce the size and

increase data storage density, we reduce the bits, so our sensor also has to be small and maintain

very, very high sensitivity. The thought gave rise to the powerful effect called “GIANT

MAGNETORESISTANCE” OR (GMR). Giant magneto resistance (GMR) came into picture in

1988, which lead the rise of spintronics. It results from subtle electron-spin effects in ultra-thin

‘multilayer’ of magnetic materials, which cause huge changes in their electrical resistance when

a magnetic field is applied. GMR is 200 times stronger than ordinary magneto resistance. It was

soon realized that read heads incorporating GMR materials would be able to sense much smaller

magnetic fields, allowing the storage capacity of a hard disk to increase from 1 to 20 gigabits.

3.2 CONSTRUCTION OF GMR

The basic GMR device consists of a three-layer sandwich of a magnetic metal such as

cobalt with a nonmagnetic metal filling such as silver. Current passes through the layers

consisting of spin-up and spin-down electrons. Those oriented in the same direction as the

electron spins in a magnetic layer pass through quite easily while those oriented in the opposite

direction are scattered. If the orientation of one of the magnetic layers can easily be changed by

the presence of a magnetic field then the device will act as a filter, or ‘spin valve’, letting through

more electrons when the spin orientations in the two layers are the same and fewer when

orientations are oppositely aligned. The electrical resistance of the device can therefore be

changed dramatically. In an ordinary electric Current, the spin points at random and plays no role

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in determining the resistance of a wire or the amplification of a transistor circuit. Spintronic

devices, in contrast, rely on differences in the transport of “spin up” and “spin down” electrons.

When a current passes through the Ferro magnet, electrons of one spin direction tend to be

obstructed.

A ferromagnetic can even affect the flow of a current in a nearby nonmagnetic metal. For

example, in the present-day read heads in computer hard drives, wherein a layer of a

nonmagnetic metal is sandwiched between two ferromagnetic metallic layers, the magnetization

of the first layer is fixed, or pinned, but the second ferromagnetic layer is not. As the read head

travels along a track of data on a computer disk, the small magnetic fields of the recorded 1’s and

0`s change the second layer’s magnetization back and forth parallel or anti parallel to the

magnetization of the pinned layer. In the parallel case, only electrons that are oriented in the

favored direction flow through the conductor easily. In the anti parallel case, all electrons are

impeded. The resulting changes in the current allow GMR read heads to detect weaker fields

than their predecessors; so that data can be stored using more tightly packaged magnetized spots

on a disk.

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CHAPTER-4SPINTRONIC DEVICES

4.1 MRAM (MAGNETORESISTIVE RANDOM ACCESS

MEMORY)

An important spintronic device, which is supposed to be one of the first spintronic

devices that have been invented, is MRAM.

Fig: 256K MRAM

Unlike conventional random-access, MRAMs do not lose stored information once the

power is turned off...A MRAM computer uses power, the four page e mail will be right there for

you. Today pc use SRAM and DRAM both known as volatile memory. They can store

information only if we have power. DRAM is a series of Capacitors; a charged capacitor

represents 1 where as an uncharged capacitor represents 0. To retain 1 you must constantly feed

the capacitor with power because the charge you put into the capacitor is constantly leaking out.

MRAM is based on integration of magnetic tunnel junction (MJT). Magnetic tunnel

junction is a three-layered device having a thin insulating layer between two metallic

ferromagnets. Current flows through the device by the process of quantum tunneling; a small

number of electrons manage to jump through the barrier even though they are forbidden to be in

the insulator. The tunneling current is obstructed when the two ferromagnetic layers have opposite

orientations and is allowed when their orientations are the same. MRAM stores bits as magnetic

polarities rather than electric charges. Then a big polarity points in one direction it holds1, when its

polarity points in other direction it holds 0. These bits need electricity to change the direction but not

to maintain them. MRAM is non volatile so, when you turn your computer off all the bits retain their

1`s and 0`s.

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4.2 SPIN TRANSISTOR CONCEPT

Traditional transistors use on-and-off charge currents to create bits—the binary zeroes

and ones of computer information. “Quantum spin field effect” transistor will use up-and-down

spin states to generate the same binary data. One can think of electron spin as an arrow; it can

point upward or downward; “spin-up and spin-down can be thought of as a digital system,

representing the binary 0 and 1. The quantum transistor employs also called “spin-flip”

mechanism to flip an up-spin to a downspin, or change the binary state from 0 to 1. In the spin

FET, both the source and the drain are ferromagnetic. The source sends spin polarized electrons

in to the channel, and this spin current flow easily if it reaches the drain unaltered (top). A

voltage applied to the gate electrode produces an electric field in the channel, which causes the

spins of fast-moving electrons to process, or rotate (bottom). The drain impedes the spin current

according to how far the spins have been rotated. Flipping spins in this way takes much less

energy and is much faster than the conventional FET process of pushing charges out of the

channel with a larger electric filed.

Fig: Spin Transistor

Table:Comparision

Electronic Devices Spintronic devices

1. Based on properties of charge of

the electron

1. Based on intrinsic property spin

of electron

2. Classical property 2. Quantum property

3. Controlled by an external electric

field in modern electronics

3. Controlled by external magnetic

field

4. Materials: conductors and

semiconductors

4.Materials: ferromagnetic

Materials

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5.Based on the number of charges

and their energy

5. Two basic spin states; spin-up

and spin-down

6. Speed is limited and power

dissipation is high

6. Based on direction of spin and

spin coupling, high speed

4.3 QUANTUM COMPUTER

In a quantum computer, the fundamental unit of information (called a quantum bit or

qubit), is not binary but rather more quaternary in name. This qubit property arises as a direct

consequence of its adherence to the laws of quantum mechanics. A qubit can exist not only in a

state corresponding to the logical state 0 or 1 as in a classical bit, but also in states corresponding

to a blend or superposition of these classical states.

Each electron spin can represent a bit; for instance, a 1 for spin up and 0 for spin down.

With conventional computers, engineers go to great lengths to ensure that bits remain in stable,

Well-defined states. A quantum computer, in contrast, lies on encoding information within

quantum bits, or qubits, each of which can exist in a superposition of 0 and 1. By having a large

number of qubits in superposition of alternative states, a quantum computer intrinsically contains

a massive parallelism. Unfortunately, in most physical systems, interactions with the surrounding

environment rapidly disrupt these superposition states. A typical disruption would effectively

change a superposition of 0 and 1 randomly into either a 0 or a 1, as process called decoherence.

State-of-the-art qubits based on the charge of electrons in a semiconductor remain coherent for a

few picoseconds at best and only at temperatures too low for practical applications. The rapid

decoherence occurs because the electric force between charges is strong and long range. In

traditional semiconductor devices, this strong interaction permits delicate control of current flow

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with small electronic fields. To quantum coherent devices, however, it is disadvantage. As a

result, an experiment was conducted on the qubits, which are based on the electron-spin.

Electron-spin qubits interact only weakly with the environment surrounding them, principally

through magnetic fields that are non-uniform in space or changing in time. The goal of the

experiment was to create some of these coherent spin states in a semiconductor to see how long

they could survive. Much to the surprise, the optically excited spin states in ZnSe remained

coherent for several nanoseconds at low temperatures—1,000 times as long as charge based

qubits. The states even survived for a few nanoseconds at room temperature. Subsequent studies

of electrons in gallium arsenide (GaAs) have shown that, under optimal conditions, spin

coherence in a semiconductor is possible.

4.4 SPINTRONIC QUBITS

1. In a conventional computer every bit has a definite value of 0 or 1. A series of eight bits an

represent any number from 0 to 255, but only one number at a time.

2. Electron spins restricted to spin up and spin down could be used as bits.

3. Quantum bits, or qubits, can also exist as super positions of 0 and 1, in effect being both

numbers at once. Eight qubits can represent every number from 0 to 255 simultaneously.

4. Electron spins are natural qubits; a tilted electron is a coherent superposition of spin up and

spins down and is less fragile than other quantum electronic states.

5.Qubits are extremely delicate: stray interactions with their surroundings degrade the

superposition extremely quickly, typically converting them in to random ordinary bits.

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CHAPTER-5

CONCLUSION

So with this paper we have proved that the new generation of computing and information

technology is on its way to revolutionize the 21st century. We believe it makes sense instead to

build on the extensive foundations of conventional electronic semiconductor technology; we

exploit the spin of the electron and create new devices and circuits, which could be more

beneficial.

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REFERENCES:

www.dac.neu.edu

www.physics.udel.edu

www.nano.caltech.edu

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