SPINTRONICS …… A QUANTUM LEAP PRESENTED BY: DEEPAK 126/05

WHAT DOES IT MEAN ? Spintronics, short for spin electronics, is the study of electron spin in materials in order to better understand its behavior, & fabricate devices that specifically exploit spin properties Spintronics utilizes the electron’s spin to create useful sensors, memory and logic devices with properties not possible with charge based devices..

Conventional electronic devices rely on the transport of electrical charge carriers - electrons - in a semiconductor such as silicon. Now, physicists are trying to exploit the 'spin' of the electron rather than its charge to create a remarkable new generation of 'spintronic' devices

SPIN OF AN ELECTRON Circulating charges on the sphere amount to tiny loops of electric current, which create a magnetic field similar to the earth's magnetic field.

WHY DO WE NEED SPINTRONICS? To further enhance the speed Diminishing size of memory cells Further compaction in the size of ICs (below 100nm) To avoid the unnecessary dissipation of heat Requirement for a non-volatile magnetic memory

Practical Application MRAM (magnetoresistive random access memory) is a method of storing data bits using magnetic charges instead of the electrical charges used by DRAM . A metal is magnetoresistive if it shows a slight change in electrical resistance when placed in a magnetic field. Conventional (RAM) chips store information as long as electricity flows through them. Once power is turned off, the information is lost . MRAM retains data after a power supply is cut off. Replacing DRAM with MRAM could prevent data loss and enable computers that start instantly, without waiting for software to boot up.

MAGNETIC MEMORY(MRAM)

FEATURES OF MRAM MRAM uses electron spins to encode data. Very High Cell densities Non- volatile memory and hence retain the information put into it. About 1000 times speed over the permanent memories of Flash type that are used today for mobile electronics. Each cell is a submicronic MTJ (Magnetic tunnel junction) and the states “0”and “1”of the cell corresponds respectively to the parallel and antiparallel configurations of the magnetic moments of electrodes of the MTJ

Ferromagnetic material Bits are stored as charges CONVENTIONAL MEMORY MRAM Dynamic ICs Ferromagnetic material Bits are stored as charges Bits are stored as magnetic moment Volatile Non-Volatile Sensor current is not spin specific Sensor current is electron spin specific More space to store a bit Less space to store a bit

HOW THE R/W HEAD READS THE INFORMATION ON THE BIT CELL? The disc drive spins underneath the header The magnetization of the bit cell alters the current flowing through the read head The current flows for a binary 0 and an ideal reader has infinite resistance for binary 1 The greater the change in resistance of the head for the two binary values greater is the sensitivity of the read head

GIANT MAGNETORESISTANCE ELECTRONS ELECTRONS RESISTANCE WORKS MAGNETIC NON MAGNETIC THE GMR EFFECT (HOW IT WORKS) GMR READER

WHY SPINTRONICS IS BETTERTHAN CONVENTIONAL ELECTRONICS? It could be used to make more smaller, more versatile and more robust chips than those currently making up silicon chips and circuit elements. No constant voltage is required to remember the states of the data because of the non–volatile property of spintronic devices. MRAM developed through spintronics has the potential to combine the speed of SRAM, the density of DRAM, and the non-volatility of Flash.

FURTHER RESEARCH IN THE FIELD OF SPINTRONICS . University of New South Wales July 27, 2006 researchers at the University of New South Wales have created: a tiny wire that doesn’t even use electrons to carry a current. Known as a hole quantum wire, it exploits the gaps – or holes - between electrons: unlike in a conventional electrical wire, the current flows in the absence of electrons Shrinking Storage Media Down to the Nanoscale Brookhaven National Laboratory March 14, 2006 researchers has fabricated magnetic films by depositing magnetic materials in patterns of dots or ellipses across a surface of nonmagnetic substrates such as carbon or silicon nitride. With each dot measuring about 100 nanometers, the could serve as building blocks data storage media

CHALLENGES FACED IN THE DEVELOPMENT OF SPINTRONIC DEVICES Basic spintronics transport requirement is to introduce & sustain large spin-polarized currents in electronic materials (semiconductors) for long times. This has yet been accomplished Issues regarding how placing a semiconductor in contact with another material would impede spin transport across the interface.

CONCLUSIONS Spintronics is heralding a new era of computer IC chips, memory units and transistors. With the advent of this new technology the diminishing size of the chips is not any problem so far. Although the research in this field is not yet complete but spintronics holds a great promise for the forthcoming computer devices.

REFERNCES “Spintronic Materials and Devices”: Past, present and future!” 0 Stuart S.P. Parkin -7803-8684-1/04/$20.00 02004 IEEE “Semiconductor Spintronics”, Hiro Akinaga and Hideo Ohno, Member, IEEE (2002) “Issues , concepts and Challenges in Spintronics” S.Das Sarma, Jaroslav Fabin & Igor Zutic ,IEEE Device Research conference (2000) “Spintronics”,Sankar Das Sarma,American Scientist Volume 89 Http://www.physics.umd.edu/rgroups/spin

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