51366050 spin valve transistor.ppt

7/28/2019 51366050 Spin Valve Transistor.ppt

1/22

A step towards quantum computers

By Shashank Shetty


2/22

Index: Introduction

Construction

Working Magnetic sensitivity

Temperature effects

Applications

Advantages

Conclusion


3/22

Introduction:

Its a spintronics device.

Conduction is due to spin polarization of

electronics.

Two experiments in 1920s suggested spin as

an additional property of an electron:

1. Closely spaced splitting of hydrogen

spectralines

2. Stern-Gerlach experiment


4/22


5/22

The starting material for both emitter andcollector is a 380um, 5-10Ocm, n-si (100)wafer.

Wafer is dry oxidised to anneal the implantand to form a SIO2 layer.


6/22

The hydrophobic surface of emitter iscontacted to the multilayer surface, forming abond through spontaneous adhesion.

Base multilayer is rf sputtered through a lasercut metal shadow mask on the collector

surface.


7/22

Working


8/22

Working(contd..) The collector barrier height about 0.7eV while the

emitter barrier height is 0.6eV.

After accelerating the electrons from emitter theyconstitute a hot Ballistic electrons in the base.

Current gain is given by,

o = (Jc Jleak ) / Je = c e qm e-w/y

where,e = emitter efficiency

c = collector efficiency


9/22

Working(contd..) qm = quantum mechanical transmission

W = base width

= the hot electron mean free path e-w/= the probability of transmission of the hot

electrons through the base

Jc =the total collector current Jleak = the collector leakage current

Je=the injected emitter current


10/22

Working(contd..) Collector current is given by

Jc = Jc+ + Jc- = Jc c e qm [ Pi+ + Pi-] + Jleak

i i The sum of the transmission probability factors for the

two spin channels can be written as

= [ Pi+ + Pi- ] = e-wcu / cu [e-wco / co

i i

e-wF/N / F/N + e-wco / co e-wF/N / F/N]


11/22

Working(contd..)At the coercive field, this quantity becomes.

= [ Pi+ + Pi- ] AP = e-wcu / cu [2e-wco /2co

i ie-wF/N / 2F/N e-wco / 2co e-wF/N / 2F/N]

Wco=the sum of all Co layer widths

Wcu=the total Cu thickness.

exp. (-WF/N /F/N()), a spin dependent factorwhich takes into account the spin dependentscattering at the interfaces.


12/22

MAGNETIC SENSITIVITY

The leakage current is quiet large (30A) and

exceeds the magneto current for an injection

current of 100mA because of low barrier

height and large collector area.

To reduce the leakage current to acceptible

value, Magneto current measurements havebeen performed at 77 K.


13/22

MAGNETIC SENSITIVITY(CONTD..)

Magnetic sensitivity of collector current at different

temperatures


14/22

Temperature effects

The collector current across the spinvalve changes its relative orientation

of magnetic movements at finite

temperature. The parallel collector current is

increasing up to 200 K and decreasing

after that, while anti-parallel collectorcurrent is increasing up to room

temperature.


15/22

Temperature effects(contd..)

Two different mechanisms aresuggested. One of them is spatial

distribution of Schottky barrier diode.

This may explain the behaviors of bothparallel and antiparallel collector

current upto 200K.

Spin mixing is spin flip process bythermal spin wave emission or

absorption at finite temperatures.


16/22

Used as stable, high sensitivity magnetic

field sensorsforautomotive, robotic,mechanical engg. & data store

application.

Used as Magnetically Controlled

Parametric Amplifier & Mixer.


17/22

Used as Magnetic Signal Processor, for

control of brushless DC motors & as

Magnetic logic elements.

In log applications they have the

advantage over conventional

semiconductor chips.

Used in Quantum computing.


18/22

Advantages

Traditional transistors use on & off charge currentsto create bits. Quantum spin field effect transistorwill use up & down spin states to generate the same

binary data

A currently logic is usually carried out usingconventional electrons, while spin is used for

memory. Spintronics will combine both.


19/22

Advantages(contd..)

In most Semi Conducting transistors the relativeproportion of the up & down carries types areequal. If Ferro Magnetic material is used as the

carrier source then the ratio can be deliberatelyskewed in one direction.

Amplification and / or switching properties of theDevice can be controlled by the external magnetic

field applied to the device. Spin current releases heat but it is rather less.


20/22

Spin valve transistor is more versatile andmore robust.

Implementing it on a whole circuit will requiresome clever ideas as controlling the spinremains the greatest hurdle.

However the key question will be whether anypotential benefit of such technology will be

worth the production cost.


21/22

QUESTIONS??


22/22

THANK YOU

51366050 spin valve transistor.ppt

Documents