SPINTRONICS Prepared By The Future Belongs To Spintronics

SPINTRONICS Prepared By :

The Future Belongs To Spintronics OUTLINE v v v v Why Spintronics? What is Spintronics? Principle Fabrication & Working of spin devices Electronics Vs. Spintronics Applications Conclusion

Why Spintronics? Moore’s Law: No. of Transistor doubles in every 18 months Complexity: Complex Chip Design & Power Loss Motivation: Spintronics-Information is carried not by electron charge but by it’s spin.

What is Spintronics? Spintronics is a blend of electronics with spin. It refers to the study of the role played by the electron spin in solid state physics and possible devices that specifically exploits spin properties of electrons instead of it’s charge. It promises new logic devices which enhances functionality, high speed and reduced power consumption.

Principle Spintronics is based on the spin of electrons rather than its charge. Every electron exist in one of the two statesspin-up and spin-down, with spins either positive half or negative half. 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.

Principle 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. 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.

Principle These have tiny regions called domains in which an excess of electrons have spins with axis pointing either up or down. The domains are randomly scattered and evenly divided between majority-up and majority-down. But, an externally applied magnetic field will line up the domains in the direction of the field. This results in a permanent magnet.

Principle When a pool of spin-polarized electrons is put in a magnetic field, precession occurs. The frequency and direction of rotation depends on the strength of magnetic field and characteristics of the material. Thus, if a voltage pushes an electron out of gallium arsenide into zinc selenide, the electron precession characteristics change. However, if a higher voltage pushes the electron sharply into zinc selenide, the electron precession characteristics don’t change.

Principle N-type materials rely on electrons to carry current where as P-type materials rely on holes. As the materials are of two different carrier types, an electric field is formed around their junction. This field is strong enough to pull a pool of spin coherent electrons from Ga. As immediately into Zn. Se, where coherence persist for 100 of nanoseconds. Thus, spin can be moved from one kind of semiconductor to another without the need for external electric fields.

Fabrication Ø Ø Spintronics devices involves two different approaches for designing & manufacturing. Perfecting the existing giant magneto resistance, GMR based technology by developing new materials with larger spin polarization. Finding the novel ways of both generation and utilization of spin polarized current. The later one is a effective method.

Working All spintronic devices acts according to the simple scheme: The information is stored (written) into spins as a particular spin orientation (up or down). The spins, being attached to mobile electrons, carry information along a wire and the information is read at a terminal. Spin orientation of conduction electrons survives for relatively long time (nanoseconds, compared to tens of femtoseconds during which electron moment decays) which makes spintronic device useful for memory storage and magnetic sensor applications.

Working These are used for quantum computing where electron spin will represent a bit (called ‘qubit’) of information. When electron spins are alligned, this creates a large scale net magnetic moment. The basic GMR device is a 3 layer sandwich of magnetic metal (such as cobalt) with a nonmagnetic metal filling (such as silver). A current passes through the layers consisting of spin up and spin down electrons.

The electrons oriented in the same direction as the electron spin in the magnetic layer pass through quite easily while those oriented in the opposite direction are scattered. If orientation of one of the magnetic layers is changed by the presence of a magnetic field, the device will act as a filter or a spin valve letting through more electrons when spin orientation in the two layers are the same and fewer electrons when spin orientation are oppositely alligned.

The electrical resistance of the device can therefore be changed dramatically. The above diagram depicts the nature of the spin valve when the two layers are oppositely alligned.

Electronics vs. Sprintronics Ø Ø One of the main advantage of spintronics over electronics is the magnets tend to stay magnetize which is sparking in the industry an interest for replacing computer’s semiconductor based components with magnetic ones, starting with the RAM. With an all-magnetic RAM, it is now possible to have a computer that retains all the information put into it. Most importantly, there will be no ‘boot-up’ waiting period when power is turned on.

Electronics vs. Sprintronics Ø Ø Another promising feature of spintronics is that it doesn’t require the use of unique and specialized semiconductor, there by allowing it to work with common metals like Cu, Al, Ag. Spintronics will use less power than conventional electronics, because the energy needed to change spin is a minute fraction of what is needed to push charge around.

Electronics vs. Sprintronics Ø Ø Another advantage includes Nonvolatility: Spins don’t change when power is turned off. The peculiar nature of spin and quantum theory describes it point to other wonderful possibility like various logic gates whose function can be changed billion times per second.

Application Ø Ø 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.

Applications Magnetic RAM

Applications Ø Ø Ø GMR sensors find a wide range of applications: Fast and accurate position and motion sensing of mechanical components in precision engineering and robotics. Missile Guidance Position and motion sensing in computer video games. Key Hole Surgery and post operative care. Automotive sensors for fuel handling system, speed control and navigation etc.

Applications Spin Valve Transistors: It is based on magneto resistance, found in multi layers (Co-Cu-Co) forming the base region. The collector current becomes strongly field dependent, the extreme magneto sensitivity makes the transistor, an interesting device for high technology hard disks and magnetic RAMs.

Conclusion With lack of dissipation, spintronics may be the best mechanism for creating ever-smaller devices. The potential market is enormous, In maybe a 10 -year timeframe, spintronics will be on par with electronics. That's why there's a huge race going on around the world In exploring Spintronics.

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