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SPINTRONICS

6-Dec-141Guide: Prof Ravi ShankarRoshan Sebastian VSUSN: 1PI14LVS121st Sem Mtech VLSI and ES The Future Belongs To Spintronics

OUTLINEWhy Spintronics?What's Spintronics?PrincipleApplications MRAMElectronics Vs. SpintronicsAdvantagesChallengesConclusion

Why Spintronics ?Failure of Moores Law : Moores Law states that the number of transistors on a silicon chip will roughly double every eighteen months. But now the transistors & other components have reached nanoscale dimensions and further reducing the size would lead to: 1. Scorching heat making making the circuit inoperable. 2. Leakage power increases RED BRICK WALL So the size of transistors & other components cannot be reduced further.

What Is Spintronics ?In conventional electronics, electron charge is used for manipulation, storage, and transfer of information . Charge scalar

Spintronics uses electron spins in addition to or in place of the electron charge. spin is vector

Spin does not replace charge current just provide extra control

Using suitable materials, many different bit states can be interpreted4Basic Principle In Spintronics , information is carried by orientation of spin rather than charge. Spin can assume one of the two states relative to the magnetic field, called spin up or spin down. These states, spin up or spin down, can be used to represent 1 and 0 in binary logic. In certain spintronic materials, spin orientation can be used as spintronic memory as these orientation do not change when system is switched off.

Disk Drive

Applications&FabricationGaint Magnetoresistance (GMR) The basic GMR device consists of a layer of non -magnetic metal between two two magnetic layers. A current consisting of spin-up and spin-down electrons is passed through the layers. Those oriented in the same direction as the electron spins in a magnetic layer pass through quite easily while those oriented in the opposite direction are scattered.

How GMR sensor read dataNSGMRRead bit 0Read bit 1NSNSNSReading CurrentMedia MagnetizationDigital Data10001 1Current cannot pass throughCurrent can pass throughSPIN VALVES If the orientation of one of the magnetic layers be changed then the device will act as a filter, or spin valve, letting through more electrons when the spin orientations in the two layers are the same and fewer when orientations are oppositely aligned. The electrical resistance of the device can therefore be changed dramatically.

Tunnel Magnetoresistance Magnetic tunnel junction has two magnetic layers separated by an insulating metal-oxide layer. Is similar to a GMR spin valve except that a very thin insulator layer is sandwitched between magnetic layers instead of metal layer . The difference in resistance between the spin-aligned and nonaligned cases is much greater than for GMR device infact 1000 times higher than the standard spin valve.

NiFe (free layer)CoFe (fixed layer)RuCoFe (pinned layer)4nm1..2nm3nm3nmAl2O3 (tunneling barrier)Magnetoresistive Random Access Memory (MRAM)

MRAM uses magnetic storage elements.The elements are mostly tunnel junctions formed from two ferromagnetic plates, each of which can hold a magnetic field, separated by a thin insulating layer.

Transistor is ON

Measuring of electrical resistance of a small sense current from a supply line through the cell to the ground.

MRAM: Reading processMRAM: Writing process

Transistor is OFF

When current is passed through the write lines, aninduced magnetic fieldis created at the junction, which alters the polarity of the free layer.

In order to change the polarity of the free layer, both fields are necessary.

Only the bit in which current is applied in both hard and easy axis will be written. The other bits will remain half-select.MRAM: Writing processSRAM VS DRAM VS MRAM VS FLASHfast speedcheapdensenon-volatileconsume low powerno need to refreshFLASHSRAM DRAMMRAM

Electronics Vs. SpintronicsELECTRONIC DEVICESSPINTRONIC DEVICES1. Based on properties of charge ofthe electron.1. Based on intrinsic property spinof the electron.2. Classical property.2. Quantum property.3. Controlled by an external electricfield in modern electronics.3. Controlled by external magneticField.4. Materials: conductors andSemiconductors.4.Materials: FerromagneticMaterials.5. Based on the number of chargesand their energy.5. Two basic spin states; spin-upand spin-down.6. Speed is limited and powerdissipation is high.6. Based on direction of spin andspin coupling, high speed.Advantage Spintronics Low power consumption.

Less heat dissipation.

Spintronic memory is non-volatile.

Takes up lesser space on chip, thus more compact.

Spin manipulation is faster , so greater read & write speed.

Spintronics does not require unique and specialized semiconductors. Common metals such as Fe, Al, Ag , etc. can be used.

Controlling spin for long distancesDifficult to INJECT and MEASURE spinInterfernce of fields with nearest elements Control of spin in silicon is difficultChallengesConclusionInterest in spintronics arises, from the looming problem of exhausting the fundamental physical limits of conventional electronics. complete reconstruction of industry is unlikely Embedded device possibleTo Quantum computers through spintronics.

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