Spintronics (a neologism acceptation "spin carriage electronics"12), aswell accepted as magnetoelectronics, is an arising technology that exploits both the built-in circuit of the electron and its associated alluring moment, in accession to its axiological cyberbanking charge, in solid-state devices.
Saturday, February 4, 2012
History
Spintronics emerged from discoveries in the 1980s apropos spin-dependent electron carriage phenomena in solid-state devices. This includes the ascertainment of spin-polarized electron bang from a ferromagnetic metal to a accustomed metal by Johnson and Silsbee (1985),3 and the analysis of behemothic magnetoresistance apart by Albert Fert et al.4 and Peter Grünberg et al. (1988).5 The origins of spintronics can be traced aback even added to the ferromagnet/superconductor tunneling abstracts pioneered by Meservey and Tedrow,6 and antecedent abstracts on alluring adit junctions by Julliere in the 1970s.7 The use of semiconductors for spintronics can be traced aback at atomic as far as the abstract angle of a circuit field-effect-transistor by Datta and Das in 1990.8
Theory
The circuit of the electron is an angular drive built-in to the electron that is abstracted from the angular drive due to its alternate motion. The electron's circuit is 1/2\hbar, implying that the electron acts as a Fermion by the spin-statistics theorem. Like alternate angular momentum, the circuit has an associated alluring moment, the consequence of which is bidding as
m=\frac{\sqrt{3}}{2}\frac{q}{m_e}\hbar.
In a solid the circuit of abounding electrons can act calm to affect the alluring and cyberbanking backdrop of a material, for archetype allotment a actual with a abiding alluring moment as in a ferromagnet.
In abounding materials, electron spins are appropriately present in both the up and the down state, and no carriage backdrop are abased on spin. A spintronic accessory requires a adjustment to accomplish or dispense a spin-polarized citizenry of electrons, this agency there is an balance of circuit up or circuit down electrons. The animosity of any circuit abased acreage X can be accounting as
P_X=\frac{X_{\uparrow}-X_{\downarrow}}{X_{\uparrow}+X_{\downarrow}}.
A net circuit animosity can be accomplished either through creating an calm activity agreeable amid circuit up and circuit down such as putting a actual in a ample alluring acreage (Zeeman effect) or the barter activity present in a ferromagnet; or banishment the arrangement out of equilibrium. The aeon of time that such a non-equilibrium citizenry can be maintained is accepted as the circuit lifetime, τ. In a deviating conductor, a circuit circulation breadth λ can aswell be authentic as the ambit over which a non-equilibrium circuit citizenry can propagate. Circuit lifetimes of advice electrons in metals are almost abbreviate (typically beneath than 1 nanosecond), and a abundant accord of analysis in the acreage is adherent to extending this lifetime to technologically accordant timescales.
A artifice assuming a circuit up, circuit down, and the consistent circuit polarized citizenry of electrons. Central a circuit injector, the animosity is constant, while alfresco the injector, the animosity decays exponentially to aught as the circuit up and down populations go to equilibrium.
There are abounding mechanisms of adulteration for a circuit polarized population, but they can be broadly classified as spin-flip drop and circuit dephasing. Spin-flip drop is a action central a solid that does not conserve spin, and can accordingly forward an admission circuit up accompaniment into an approachable circuit down state. Circuit dephasing is if a citizenry of electrons with a accepted circuit state, precess at altered rates, accident the accepted circuit accompaniment over time. In bedfast structures, circuit dephasing can be suppressed, arch to circuit lifetimes of milliseconds in semiconductor breakthrough dots at low temperatures.
By belief new abstracts and adulteration mechanisms, advisers achievement to advance the achievement of applied accessories as able-bodied as abstraction added axiological problems in abridged amount physics.
m=\frac{\sqrt{3}}{2}\frac{q}{m_e}\hbar.
In a solid the circuit of abounding electrons can act calm to affect the alluring and cyberbanking backdrop of a material, for archetype allotment a actual with a abiding alluring moment as in a ferromagnet.
In abounding materials, electron spins are appropriately present in both the up and the down state, and no carriage backdrop are abased on spin. A spintronic accessory requires a adjustment to accomplish or dispense a spin-polarized citizenry of electrons, this agency there is an balance of circuit up or circuit down electrons. The animosity of any circuit abased acreage X can be accounting as
P_X=\frac{X_{\uparrow}-X_{\downarrow}}{X_{\uparrow}+X_{\downarrow}}.
A net circuit animosity can be accomplished either through creating an calm activity agreeable amid circuit up and circuit down such as putting a actual in a ample alluring acreage (Zeeman effect) or the barter activity present in a ferromagnet; or banishment the arrangement out of equilibrium. The aeon of time that such a non-equilibrium citizenry can be maintained is accepted as the circuit lifetime, τ. In a deviating conductor, a circuit circulation breadth λ can aswell be authentic as the ambit over which a non-equilibrium circuit citizenry can propagate. Circuit lifetimes of advice electrons in metals are almost abbreviate (typically beneath than 1 nanosecond), and a abundant accord of analysis in the acreage is adherent to extending this lifetime to technologically accordant timescales.
A artifice assuming a circuit up, circuit down, and the consistent circuit polarized citizenry of electrons. Central a circuit injector, the animosity is constant, while alfresco the injector, the animosity decays exponentially to aught as the circuit up and down populations go to equilibrium.
There are abounding mechanisms of adulteration for a circuit polarized population, but they can be broadly classified as spin-flip drop and circuit dephasing. Spin-flip drop is a action central a solid that does not conserve spin, and can accordingly forward an admission circuit up accompaniment into an approachable circuit down state. Circuit dephasing is if a citizenry of electrons with a accepted circuit state, precess at altered rates, accident the accepted circuit accompaniment over time. In bedfast structures, circuit dephasing can be suppressed, arch to circuit lifetimes of milliseconds in semiconductor breakthrough dots at low temperatures.
By belief new abstracts and adulteration mechanisms, advisers achievement to advance the achievement of applied accessories as able-bodied as abstraction added axiological problems in abridged amount physics.
Metal-based spintronic devices
The simplest adjustment of breeding a spin-polarised accepted in a metal is to canyon the accepted through a ferromagnetic material. The a lot of accepted appliance of this aftereffect is a behemothic magnetoresistance (GMR) device. A archetypal GMR accessory consists of at atomic two layers of ferromagnetic abstracts afar by a spacer layer. When the two magnetization vectors of the ferromagnetic layers are aligned, the electrical attrition will be lower (so a college accepted flows at connected voltage) than if the ferromagnetic layers are anti-aligned. This constitutes a alluring acreage sensor.
Two variants of GMR accept been activated in devices: (1) current-in-plane (CIP), area the electric accepted flows alongside to the layers and (2) current-perpendicular-to-plane (CPP), area the electric accepted flows in a administration erect to the layers.
Other metals-based spintronics devices:
Adit Magnetoresistance (TMR), area CPP carriage is accomplished by application quantum-mechanical tunneling of electrons through a attenuate insulator amid ferromagnetic layers.
Spin Torque Transfer, area a accepted of spin-polarized electrons is acclimated to ascendancy the magnetization administration of ferromagnetic electrodes in the device.
edit Applications
Read active of avant-garde harder drives are based on the GMR or TMR effect.
Motorola has developed a 1st bearing 256 kb MRAM based on a individual alluring adit alliance and a individual transistor and which has a read/write aeon of beneath 50 nanoseconds9 (Everspin, Motorola's spin-off, has back developed a 4 Mbit version10). There are two 2nd bearing MRAM techniques currently in development: Thermal Assisted Switching (TAS)11 which is getting developed by Crocus Technology, and Spin Torque Transfer (STT) on which Crocus, Hynix, IBM, and several added companies are working.12
Another architecture in development, alleged Racetrack memory, encodes advice in the administration of magnetization amid area walls of a ferromagnetic metal wire.
There are Alluring sensors application the GMR effect.
Two variants of GMR accept been activated in devices: (1) current-in-plane (CIP), area the electric accepted flows alongside to the layers and (2) current-perpendicular-to-plane (CPP), area the electric accepted flows in a administration erect to the layers.
Other metals-based spintronics devices:
Adit Magnetoresistance (TMR), area CPP carriage is accomplished by application quantum-mechanical tunneling of electrons through a attenuate insulator amid ferromagnetic layers.
Spin Torque Transfer, area a accepted of spin-polarized electrons is acclimated to ascendancy the magnetization administration of ferromagnetic electrodes in the device.
edit Applications
Read active of avant-garde harder drives are based on the GMR or TMR effect.
Motorola has developed a 1st bearing 256 kb MRAM based on a individual alluring adit alliance and a individual transistor and which has a read/write aeon of beneath 50 nanoseconds9 (Everspin, Motorola's spin-off, has back developed a 4 Mbit version10). There are two 2nd bearing MRAM techniques currently in development: Thermal Assisted Switching (TAS)11 which is getting developed by Crocus Technology, and Spin Torque Transfer (STT) on which Crocus, Hynix, IBM, and several added companies are working.12
Another architecture in development, alleged Racetrack memory, encodes advice in the administration of magnetization amid area walls of a ferromagnetic metal wire.
There are Alluring sensors application the GMR effect.
Semiconductor-based spintronic devices
Ferromagnetic semiconductor sources (like manganese-doped gallium arsenide GaMnAs),13 access the interface attrition with a adit barrier,14 or application hot-electron injection.15
Spin apprehension in semiconductors is addition challenge, which has been met with the afterward techniques:
Faraday/Kerr circling of transmitted/reflected photons16
Circular animosity assay of electroluminescence17
Nonlocal circuit valve (adapted from Johnson and Silsbee's plan with metals)18
Ballistic circuit filtering19
The closing address was acclimated to affected the abridgement of spin-orbit alternation and abstracts issues to accomplish circuit carriage in silicon, the a lot of important semiconductor for electronics.20
Because alien alluring fields (and devious fields from alluring contacts) can could cause ample Hall furnishings and magnetoresistance in semiconductors (which actor spin-valve effects), the alone absolute affirmation of circuit carriage in semiconductors is affirmation of circuit antecedence and dephasing in a alluring acreage non-collinear to the injected circuit orientation. This is alleged the Hanle effect.
Spin apprehension in semiconductors is addition challenge, which has been met with the afterward techniques:
Faraday/Kerr circling of transmitted/reflected photons16
Circular animosity assay of electroluminescence17
Nonlocal circuit valve (adapted from Johnson and Silsbee's plan with metals)18
Ballistic circuit filtering19
The closing address was acclimated to affected the abridgement of spin-orbit alternation and abstracts issues to accomplish circuit carriage in silicon, the a lot of important semiconductor for electronics.20
Because alien alluring fields (and devious fields from alluring contacts) can could cause ample Hall furnishings and magnetoresistance in semiconductors (which actor spin-valve effects), the alone absolute affirmation of circuit carriage in semiconductors is affirmation of circuit antecedence and dephasing in a alluring acreage non-collinear to the injected circuit orientation. This is alleged the Hanle effect.
Applications
Applications such as semiconductor lasers application spin-polarized electrical bang accept apparent beginning accepted abridgement and controllable circularly polarized articular ablaze output.21 Future applications may cover a spin-based transistor accepting advantages over MOSFET accessories such as steeper sub-threshold slope.
Magnetic Adit Transistor: The alluring adit transistor with a individual abject layer, by van Dijken et al. and Jiang et al.22, has the afterward terminals:
Emiter (FM1): It injects spin-polarized hot electrons into the base.
Abject (FM2): Spin-dependent drop takes abode in the base. It aswell serves as a circuit filter.
Beneficiary (GaAs): A Schottky barrier is formed at the interface. This beneficiary regions alone collects electrons if they accept abundant activity to affected the Schottky barrier, and if there are states accessible in the semiconductor.
The magnetocurrent (MC) is accustomed as:
MC = \frac{I_{c,p}-I_{c,ap}}{I_{c,ap}}
And the alteration arrangement (TR) is
TR = \frac{I_C}{I_E}
MTT promises a awful spin-polarized electron antecedent at allowance temperature.
Magnetic Adit Transistor: The alluring adit transistor with a individual abject layer, by van Dijken et al. and Jiang et al.22, has the afterward terminals:
Emiter (FM1): It injects spin-polarized hot electrons into the base.
Abject (FM2): Spin-dependent drop takes abode in the base. It aswell serves as a circuit filter.
Beneficiary (GaAs): A Schottky barrier is formed at the interface. This beneficiary regions alone collects electrons if they accept abundant activity to affected the Schottky barrier, and if there are states accessible in the semiconductor.
The magnetocurrent (MC) is accustomed as:
MC = \frac{I_{c,p}-I_{c,ap}}{I_{c,ap}}
And the alteration arrangement (TR) is
TR = \frac{I_C}{I_E}
MTT promises a awful spin-polarized electron antecedent at allowance temperature.
Subscribe to:
Posts (Atom)