Spin Valve Transistor…A STEP TOWARDS QUANTUM COMPUTER

KSHITIJ TAMBI ( M. BHADU )(07EEBEE024) Asst.Prof. Dept. E.E.

Engineering College Bikaner

What is Spin Valve Transistor?Spin valve transistor is different

from conventional transistor. In this for conduction spin polarization of electrons is used. Only electrons with correct spin polarization can travel successfully through the device.

Spin valve transistor came into light by the advent of Giant Magneto Resistance (GMR) in 1988. GMR is 200 times stronger than ordinary Magneto Resistance.It results from subtle electron – spin effects in ultra multilayers of magnetic materials that cause a huge change in electrical resistance.

Spin valve transistor is based on the spin of electrons rather than its charge.

Every electron exist in one of the two states-spin-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.

SPIN VALVE TRANSISTOR

Schematic layout of the spin-valve transistor (left) and a transmission electron microscope image of the cross section of a real device (right).

Spin Valve Transistor: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.

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.

o These are used for quantum computing where electron spin will represent a bit (called ‘qubit’) of information.

When electron spins are aligned, 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 non-magnetic metal filling (such as silver).

A current passes through the layers consisting of spin up and spin down electrons.

In spin valve transistor (SVT) electrons are injected in to metallic base across a Schottky barrier (Emitter side) pass through the spin valve and reach the opposite side (Collector side) of transistor. When these injected electrons traverse the metallic base electrons are above Fermi level, hence hot electron magneto transport should be considered in Spin Valve Transistor (SVT).

The transport properties of hot electrons are different from Fermi electrons.For example spin polarisation of Fermi electrons mainly depends on Density Of States (DOS) at Fermi level, while the spin polarisation of hot electron is related to the density of unoccupied states above the fermi level.

APPLICATIONS:

Spin transistors have huge potential for incorporation in stable, high sensitivity magnetic field sensors for automotive, robotic, mechanical engg. & data storage applications. This may also be used as Magnetically Controlled Parametric Amplifiers & Mixers, as magnetic signal processors, for control of brush less DC motors & as Magnetic Logic elements

In log applications they have the advantage over conventional semiconductor chips that they do not require power to maintain their memory slate. It finds its application towards Quantum Computer, a new trend in computing. Here we use bits instead of bits . Qubit also represents only 1& 0 but here they show superposition these classical states. But it is in pioneering stage.

ADVANTAGES OVER ELECTRONIC TRANSISTOR :-

1. Traditional transistors use on & off charge currents to create bits –the binary 0&1 of Computer information. Quantum spin field effect transistor will use up & down spin states to generate the same binary data.2. A currently logic is usually carried out using conventional electrons, while spin is used for memory. Spintronics will combine both. 3. In most Semi Conducting transistors the relative proportion of the up & down carries types are equal.

If Ferro Magnetic material is used as the carrier source then the ratio can be deliberately skewed in one direction. 4. Amplification and / or switching properties of the Device can be controlled by the external magnetic field applied to the device.5. One of the problems of charge current electrons is that we pack more devices together, the chip heats up. Spin current releases heat but it is rather less.

6. Spin valve transistor uses less power than conventional transistors,because the energy needed to change the spin is a minute fraction of what is needed to push a charge around.

7. Another advantage includes Non-volatility: Spins don’t change when power is turned off.

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.