Spintronics hard copy

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Spintronics hard copy

  1. 1. TECHNICAL SEMINAR ON SPINTRONIC TECHNOLOGY Submitted in Partial Fulfillment of the requirement For the award of degree of Bachelor of Technology InELECTRONICS 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) 1
  2. 2. Certificate This is to certify that the mini project report entitled SPINTRONIC TECHNOLOGY isbeing submitted by A. DIVYAJYOTHI in partial fulfillment of the requirement for the award ofdegree in Bachelor of Technology in Electronics and Communication Engineering during theperiod 2009-2013. This is a record of students own work carried out by them under oursupervision and guidance. The matter enclosed in this project report has not been submitted for the award of anyother Degree. D.V.RAJESHWAR RAJU. B.SWAMY. Coordinator Head of the Department ACKNOWLEDGEMENT 2
  3. 3. My special thanks to Mrs.D.RAMADEVI, Principal and management forproviding all the facilities required for completing this seminar. We are very grateful to Mr.B.SWAMY, Head of the department, andELECTRONICS AND COMMUNICATION ENGINEERING for his inspiring guidanceand 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 eachstage of this project work. ABSTRACT 3
  4. 4. Keywords:(GMR) “Spintronics” is an emergent NANO technology, which uses the spin of an electroninstead 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 thepassage of spin-up and spin-down electrons differently the paper starts with the detail descriptionof the fundamentals and properties of the spin of the electrons. It proceeds with a note onmagneto resistance, the development of Giant Magneto resistance (GMR) and devices likeMagneto Random Access Memory, which are the new version of the traditional RAMs. Itdescribe how this new version of RAMs which can revolutionize the memory industry. There isalso detailed explanation of the way, how this revolution can increase the data density in ourmemory systems. It is followed by an account of new Spin Field Effect Transistors. It alsospecifies the differences between electronic devices and spintronic devices. It also gives thehurdles due to the presence of holes. This paper also discusses about a quantum computer, whichuses qubits rather than normal binary digits for computations. It also gives the hurdles due to thepresence of holes. Finally it ends with a note on why we should switch on this technology. Ranroad track and conveyor belts kept the Ford’s assemble line running. At that time, his method ofproduction was lauded and was considered most efficient. But that ford’s assembly plant, whichwas only eulogized in his time, will look strange to those who were born and raised up in the21st century. Because the machines in the next 50 years will get increasingly smaller – so smallthat thousands of machines will fit into the full stop at the end of this line. This branch ofengineering 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 toreplace conventional electronics in the near future, i.e. “spintronics”. Chapter-1 INTRODUCTION 4
  5. 5. 1.1 SPINTRONICS Imagine a data storage device of the size of an atom working at a speed of light. Imaginea microprocessor whose circuits could be changed on the fly. One minute is could be optimizedfor data base access. The next for transaction processing and the next for scientific numbercrunching. Finally, imagine a computer memory thousands of times denser and faster thantoday’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 propertiesof an electron instead of or in addition to its charge dependent properties, Conventionalelectronics devices rely on the transport of electric charge carries electrons. But there is otherdimension of an electron other than its charge and mass i.e. spins. This dimension can beexploited to create a remarkable generation of spintronic devices. It is believed that in the nearfuture spintronics could be more revolutionary than any other thing that nanotechnology hasstirred up so far.1.2 WHY IS IT GOING TO BE ONE OF THE RAPIDLY EMERGINGFIELDS? As there is rapid progress in the miniaturization of semiconductor electronic devicesleads to a chip features smaller than 100 nanometers in size, device engineers and physists are 5
  6. 6. 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 theirfunctions from the foundations of spintronics. Information-processing technology has thus farrelied on purely charge based devices ranging from the now quantum, vaccume tube today’smillion transistor microchips. Those conventional electronic devices move electronic chargesaround, ignoring the spin that tags along that side on each electron. CHAPTER-2 ELECTRON SPIN2.1 FUNDAMENTALS OF SPIN 6
  7. 7. 1. In addition to their mass and electric charge, electrons have an intrinsic quantity of angularmomentum 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 spinaxis.3. Scientists represent the spin with a vector. For a sphere spinning “west to east”, the vectorpoints “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 currentlow.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 onedirection, or the other called spin-up or spin-down. Magnetism is an intrinsic Physical propertyassociated with the spins. An intuitive notion of how an electron spins is suggested below. Imagine a small electronically charged sphere spinning rapidly. The circulating chargesin the sphere amount to tiny loops of electric current which creates a magnetic field.. a spinningsphere in an external magnetic field changes its total energy according to how its spin vector isaligned with the spin. In some ways, an electron is just like a spinning sphere of charge, anelectron has a quantity of angular momentum (spin) an associated magnetism. In an ambient 7
  8. 8. magnetic field and the spin changing this magnetic field can change orientation. Its energy isdependent on how its spin vector is oriented. The bottom line is that the spin along with massand charge is defining characteristics of an electron,. In an ordinary electric current, the spinpoints at random and plays no role in determining the resistance of a wire or the amplification ofa transistor circuit. Spintronic devices in contrast rely on the differences in the transport of spin-up and spindown electrons. CHAPTER-3 GMR3.1 GIANT MAGNETO RESISTANCE 8
  9. 9. Magnetism is the integral part of the present day’s data storage techniques. Right fromthe Gramophone disks to the hard disks of the super computer magnetism plays an importantrole. Data is recorded and stored as tiny areas of magnetized iron or chromium oxide. To accessthe information, a read head detects the minute changes in magnetic field as the disk spinsunderneath it. In this way the read heads detect the data and sent it to the various succeedingcircuits. The magneto resistant devices can sense the changes in the magnetic field only to asmall extent, which is appropriate to the existing memory devices. When we reduce the size andincrease data storage density, we reduce the bits, so our sensor also has to be small and maintainvery, very high sensitivity. The thought gave rise to the powerful effect called “GIANTMAGNETORESISTANCE” OR (GMR). Giant magneto resistance (GMR) came into picture in1988, 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 whena magnetic field is applied. GMR is 200 times stronger than ordinary magneto resistance. It wassoon realized that read heads incorporating GMR materials would be able to sense much smallermagnetic 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 ascobalt with a nonmagnetic metal filling such as silver. Current passes through the layersconsisting of spin-up and spin-down electrons. Those oriented in the same direction as theelectron spins in a magnetic layer pass through quite easily while those oriented in the oppositedirection are scattered. If the orientation of one of the magnetic layers can easily be changed bythe presence of a magnetic field then the device will act as a filter, or ‘spin valve’, letting throughmore electrons when the spin orientations in the two layers are the same and fewer whenorientations are oppositely aligned. The electrical resistance of the device can therefore bechanged dramatically. 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. Spintronicdevices, 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 beobstructed. 9
  10. 10. A ferromagnetic can even affect the flow of a current in a nearby nonmagnetic metal. Forexample, in the present-day read heads in computer hard drives, wherein a layer of anonmagnetic metal is sandwiched between two ferromagnetic metallic layers, the magnetizationof the first layer is fixed, or pinned, but the second ferromagnetic layer is not. As the read headtravels along a track of data on a computer disk, the small magnetic fields of the recorded 1’s and0`s change the second layer’s magnetization back and forth parallel or anti parallel to themagnetization of the pinned layer. In the parallel case, only electrons that are oriented in thefavored direction flow through the conductor easily. In the anti parallel case, all electrons areimpeded. The resulting changes in the current allow GMR read heads to detect weaker fieldsthan their predecessors; so that data can be stored using more tightly packaged magnetized spotson a disk. CHAPTER-4 SPINTRONIC DEVICES4.1 MRAM (MAGNETORESISTIVE RANDOM ACCESS 10
  11. 11. Magnetism is the integral part of the present day’s data storage techniques. Right fromthe Gramophone disks to the hard disks of the super computer magnetism plays an importantrole. Data is recorded and stored as tiny areas of magnetized iron or chromium oxide. To accessthe information, a read head detects the minute changes in magnetic field as the disk spinsunderneath it. In this way the read heads detect the data and sent it to the various succeedingcircuits. The magneto resistant devices can sense the changes in the magnetic field only to asmall extent, which is appropriate to the existing memory devices. When we reduce the size andincrease data storage density, we reduce the bits, so our sensor also has to be small and maintainvery, very high sensitivity. The thought gave rise to the powerful effect called “GIANTMAGNETORESISTANCE” OR (GMR). Giant magneto resistance (GMR) came into picture in1988, 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 whena magnetic field is applied. GMR is 200 times stronger than ordinary magneto resistance. It wassoon realized that read heads incorporating GMR materials would be able to sense much smallermagnetic 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 ascobalt with a nonmagnetic metal filling such as silver. Current passes through the layersconsisting of spin-up and spin-down electrons. Those oriented in the same direction as theelectron spins in a magnetic layer pass through quite easily while those oriented in the oppositedirection are scattered. If the orientation of one of the magnetic layers can easily be changed bythe presence of a magnetic field then the device will act as a filter, or ‘spin valve’, letting throughmore electrons when the spin orientations in the two layers are the same and fewer whenorientations are oppositely aligned. The electrical resistance of the device can therefore bechanged dramatically. 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. Spintronicdevices, 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 beobstructed. 9

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