Spintronics

SLIDE 1

Introduction

Conventional electronic devices ignore the spin property and rely strictly on the transport of the electrical charge of electrons

Adding the spin degree of freedom provides new effects, new capabilities and new functionalities

SLIDE 2

Future Demands

Moore’s Law states that the number of

transistors on a silicon chip will roughly

double every eighteen months

As electronic devices become smaller,

quantum properties of the wavelike nature

of electrons are no longer negligible

Spintronic devices offer the possibility of

enhanced functionality, higher speed, and

reduced power consumption

SLIDE 3

Spintronics is a NANO technology which deals with spin dependent properties of an electron instead of charge dependent properties

Spintronics uses electron spins in addition to or in place of the electron charge.

Spintronics = Spin-based electronicsSLIDE 4

Principle

Every electron exist in one of the two states spin-

up and spin-down, with spins either positive half or

negative half.

SLIDE 5

Origin of the spin is electron’s intrinsic property

“angular momentum”

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.

Principle

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.

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.

SLIDE 6

Principle

1. These have tiny regions called domains inwhich an excess of electrons have spins withaxis pointing either up or down.

2. The domains are randomly scattered andevenly divided between majority-up andmajority-down.

3. But, an externally applied magnetic field willline up the domains in the direction of thefield. This results in a permanent magnet.

SLIDE 7

Gaint Magnetoresistance (GMR)

The basic GMR device consists of a layer of non -magnetic metal

between two magnetic layers.

A current consisting of spin-up and spin-down electrons is passed through

the layers.

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.

SLIDE 8

Advantage Of Spintronics

Low power consumption.

Less heat dissipation.

Spintronic memory is non-volatile.

Takes up lesser space on chip, thus more compact.

Spin manipulation is faster , so greater read & write speed.

Spintronics does not require unique and specialized

semiconductors.

Common metals such as Fe, Al, Ag , etc. can be used.

SLIDE 9

Applications

Spin Polarized Feild EffectTransistor (Spin-FET)

SLIDE 9

In these devices a non magnetic layer which is

used for transmitting and controlling the spin

polarized electrons from source to drain plays

a crucial role. For functioning of this device

first the spins have to be injected from source

into this non-magnetic layer and then

transmitted to the collector. These

non-magnetic layers are also called as

semimetals, because they have very large spin

diffusion lengths. The injected spins which are

transmitted through this layer start precessing

as illustrated in Figure before they reach the

collector due to the spin-orbit coupling effect.

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.

2. MRAMSLIDE 10

MRAM uses magnetic storage elements instead of electric used in

conventional RAM.

Tunnel junctions are used to read the information stored in

Magnetoresistive Random Access Memory, typically a”0” for zero point

magnetization state and “1” for antiparallel state.

MRAMSLIDE 11

MRAMMagneto resistive RAM

Array structure of MRAM

Reading: transistor of the selected bit cell turned ‘on’ + current applied in the bit line

Writing: transistor of the selected bit cell turned ‘off’ + currents applied in the bit and word lines

Need of 2 magnetic fields for writing

SLIDE 12

This technology will exploit the spin of the

electron and create new devices and circuits which could

be more beneficial in future by providing devices like

memories for data base accessing with the speed of light.

The devices of this technology are very useful for

transaction processing and for scientific number

crunching.

Moreover, these "spintronic" devices might lead

to quantum computers and quantum communication

based on electronic solid-state devices, thus changing the

perspective of information technology in the 21st century

SLIDE 13