Spintronics Devices and Applications

SPINTRONICS DEVICES AND APPLICATIONS

Conventional electronic devices rely on the transport of electrical charge carriers - electrons.

The 'spin' of the electron can be used rather than its charge to create a remarkable new generation of 'spintronic' devices. These are smaller, more versatile and more robust than those currently making up silicon chips and circuit elements.

It is a field of a nanotechnology that deals with spin dependent properties of electrons and its implication in the device applications.

Spintronics is the abbreviation of spin transport electronics, also known as spin electronics. Magneto electronics, Spin Electronics and Spintronics are different name for the use of electrons' spins (not just their electrical charge) in information circuits.

Principle

All spintronic devices act according to the simple scheme.

1. Information is stored (written) into spins as a particular spin orientation (up or down). (Fig. 5.23)

2. The spins, being associated to mobile electrons, carry the information along a wire.

3. The information is read at a terminal.

Spin orientation of conduction electrons survives for a relatively long time (nanoseconds, compared to tens of femtoseconds during which electron momentum decays).

This makes spintronic devices particularly attractive for memory storage storage and magnetic sensor applications, and potentially for quantum computing.

The electron spin will represent a bit (called qubit) of information in quantum computing.

Since the advent of spintronics our view of future electronic devices and functionalities have significantly changed.

Spintronics links the conventional microelectronic functionality of semiconductor building blocks to the nonvolatility of magnetic building blocks.

Spintronics devices

Spin valve

A spin valve is a device which provides the Giant Magneto resistive effect. The device can be made to be highly resistive or highly conductive depending on the direction of the applied magnetic fields in the conducting layers. This technology offers very fast switching speeds and reduced power consumption. (Fig. 5.24)

Spin - FET

A spin based Field Effect Transistor ie., SPIN-FET structure is shown in fig 5.25.

For functioning of this device, first the spins have to be injected from source into the non-magnetic layer and then transmitted to the collector.

The injected spins which are transmitted through this layer start precessing as illustrated in fig 5.25, before they reach the collector due to the spin-orbit coupling effect.

Hence, the net spin polarization is reduced. In order to solve this problem an electrical field is applied perpendicularly to the plane of the film by depositing a gate electrode on the top to reduce the spin-orbit coupling effect.

In fig. 5.25 Vg is the gate voltage. When Vg is zero the injected spins which are transmitted through the 2DEG (2-Dimensional Electron Gas) layer starts precessing before they reach the collector, thereby reducing the net spin polarization.

When V_g >> 0 the precession of the electrons is controlled with electrical filed thereby allowing the spins to reach at the collector with the same polarization.

By controlling the gate voltage and polarity, the current in the collector can be modulated just like the MOSFET of the conventional electronics.

Spin LED

In spin LEDs the emitted light possess a polarization dependent on the spin polarization of the charge carriers involved in the recombination. Due to this spin-dependent polarization, a device such as a spin LED can be used to produce light of a specific polarization. Additionally, spin LEDs can be used in the study and development of other spintronics devices. (Fig. 5.26)

Advantages of spintronic devices over conventionale electronic devices

i. Spintronic devices are new logic devices which enhances allud to functionality, high speed and reduced power consumption.

ii. Also ultimate miniaturization is possible with less power dissipation