07-08-2012, 04:04 PM
Bluetooth Low Energy
[attachment=30436]
BASIC TERMINOLOGIES
NON-VOLATILE RAM
Non-Volatile Random Access Memory (NVRAM) is the general name used to describe any type of random access memory which does not lose its information when power is turned off. This is in contrast to the most common forms of random access memory today, DRAM and SRAM, which both require continual power in order to maintain their data. NVRAM is a subgroup of the more general class of non-volatile memory types, the difference being that NVRAM devices offer random access, like hard disks.
SPIN
In quantum mechanics, spin is a fundamental property of atomic nuclei, hadrons, and elementary particles. For particles with non-zero spin, spin direction (also called spin for short) is an important intrinsic degree of freedom.
As the name indicates, the spin has originally been thought of as a rotation of particles around their own axis. This picture is correct insofar as spins obey the same mathematical laws as do quantized angular momenta. On the other hand, spins have some peculiar properties that distinguish them from orbital angular momenta: spins may have half-integer quantum numbers, and the spin of charged particles is associated with a magnetic dipole moment in a way (g-factor different from 1) that is incompatible with classical physics.
The electron spin is the key to the Pauli Exclusion Principle and to the understanding of the periodic system of chemical elements. Spin-orbit coupling leads to the fine structure of atomic spectra, which is used in atomic clocks and in the modern definition of the fundamental unit second. Precise measurements of the g-factor of the electron have played an important role in the development and verification of quantum electrodynamics. Electron spins play an important role in magnetism, with applications for instance in computer memories. Manipulation of spins in semiconductor devices is the subject of the developing field of spintronics. The manipulation of nuclear spins by radiofrequency waves (nuclear magnetic resonance) is important in chemical spectroscopy and medical imaging. The photon spin is associated with the polarization of light.
The head-on collision of a quark (red ball) from one proton (orange ball) with a gluon (green ball) from another proton with opposite spin, spin is represented by the blue arrows circling the protons and the quark. The blue question marks circling the gluon represent the question: Are gluons polarized? Ejected from the collision are a shower of quarks and a photon of light (purple ball).
SPIN
Particles with spin can possess a magnetic dipole moment, just like a rotating electrically charged body in classical electrodynamics. These magnetic moments can be experimentally observed in several ways, e.g. by the deflection of particles by inhomogeneous magnetic fields in a Stern-Gerlach experiment, or by measuring the magnetic fields generated by the particles themselves. The intrinsic magnetic moment p of an elementary particle with charge q, mass m, and spin S, is
Where the dimensionless quantity g is called the g-factor. For exclusively orbital rotations it would be 1.
In ordinary materials, the magnetic dipole moments of individual atoms produce magnetic fields that cancel one another, because each dipole points in a random direction. Ferromagnetic materials below their Curie temperature, however, exhibit magnetic domains in which the atomic dipole moments are locally aligned, producing a macroscopic, non-zero magnetic field from the domain. These are the ordinary "magnets" with which we are all familiar.
The study of the behavior of such "spin models" is a thriving area of research in condensed matter physics. For instance, the Ising model describes spins (dipoles) that have only two possible states, up and down, whereas in the Heisenberg model the spin vector is allowed to point in any direction. These models have many interesting properties, which have led to interesting results in the theory of phase transitions.
SPIN TRANSFER
Spin transfer is the phenomenon in which the spin angular momentum of the charge carriers (usually electrons) gets transferred from one location to another. This phenomenon is responsible for several important and observable physical effects.
Most famously, spin polarized current passing into a nanoscale magnet tends to deposit some of its spin angular momentum into the magnet, thereby applying a large torque to the magnetization. This enables magnetic manipulations far more efficiently than can be achieved with magnetic fields alone, especially as device applications shrink in scale. In the hard disk industry, where a series of nanoscale magnetic layers called a spin valve is often used to measure the small local magnetic fields above the disk surface, this is an undesirable effect, as it hinders the ability to measure the state of the valve without disturbing it. In the MRAM industry, however, this effect may prove incredibly useful in reducing power consumption.
INTRODUCTION
SPINTRONICS:
Spintronics (a neologism meaning "spin transport electronics"), also known as magneto electronics, is an emerging technology which exploits the intrinsic spin of electrons and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-state devices.
Electrons are spin-1/2 fermions and therefore constitute a two-state system with spin "up" and spin "down". To make a spintronic device, the primary requirements are to have a system that can generate a current of spin polarized electrons comprising more of one spin species - up or down - than the other (called a spin injector), and a separate system that is sensitive to the spin polarization of the electrons (spin detector). Manipulation of the electron spin during transport between injector and detector (especially in semiconductors) via spin precession can be accomplished using real external magnetic fields or effective fields caused by spin-orbit interaction.
Spin polarization in non-magnetic materials can be achieved either through the Zeeman Effect in large magnetic fields and low temperatures, or by non-equilibrium methods. In the latter case, the non-equilibrium polarization will decay over a timescale called the "spin lifetime". Spin lifetimes of conduction electrons in metals are relatively short (typically less than 1 nanosecond) but in semiconductors the lifetimes can be very long (microseconds at low temperatures), especially when the electrons are isolated in local trapping potentials (for instance, at impurities, where lifetimes can be milliseconds).
Metals-based spintronic devices
The simplest method of generating a spin-polarized current in a metal is to pass the current through a ferromagnetic material. The most common application of this effect is a Giant Magneto Resistance (GMR) device. A typical GMR device consists of at least two layers of ferromagnetic materials separated by a spacer layer. When the two magnetization vectors of the ferromagnetic layers are aligned, the electrical resistance will be lower (so a higher current flows at constant voltage) than if the ferromagnetic layers are anti-aligned. This constitutes a magnetic field sensor. Two variants of GMR have been applied in devices:
• Current-In-Plane (CIP), where the electric current flows parallel to the layers.
• Current-Perpendicular-to-Plane (CPP), where the electric current flows in a direction perpendicular to the layers.
Other metals-based spintronics devices:
• Tunnel Magneto Resistance (TMR), where CPP transport is achieved by using quantum- mechanical tunneling of electrons through a thin insulator separating ferromagnetic layers.
• Spin Torque Transfer, where a current of spin-polarized electrons is used to control the magnetization direction of ferromagnetic electrodes in the device.
The storage density of hard drives is rapidly increasing along an exponential growth curve, in part because spintronics-enabled devices like GMR and TMR sensors have increased the sensitivity of the read head which measures the magnetic state of small magnetic domains (bits) on the spinning platter. The doubling period for the areal density of information storage is twelve months, much shorter than Moore's Law, which observes that the
number of transistors that can cheaply be incorporated in an integrated circuit doubles every two years.
MRAM, or magnetic random access memory, uses arrays of TMR or Spin torque transfer devices. MRAM is nonvolatile (unlike charge-based DRAM in today's computers) so information is stored even when power is turned off, potentially providing instant-on computing. Motorola has developed a 256 kb MRAM based on a single magnetic tunnel junction and a single transistor. This MRAM has a read/write cycle of fewer than 50 nanoseconds. Another design in development, called Racetrack memory, encodes information in the direction of magnetization between domain walls of a ferromagnetic metal wire.
Semiconductor-based spintronic devices
In early efforts, spin-polarized electrons are generated via optical orientation using circularly-polarized photons at the band gap energy incident on semiconductors with appreciable spin-orbit interaction (like GaAs and ZnSe). Although electrical spin injection can be achieved in metallic systems by simply passing a current through a ferromagnet, the large impedance mismatch between ferromagnetic metals and semiconductors prevented efficient injection across metal-semiconductor interfaces. A solution to this problem is to use ferromagnetic semiconductor sources (like manganese-doped gallium arsenide GaMnAs), increasing the interface resistance with a tunnel barrier, or using hot-electron injection.
[attachment=30436]
BASIC TERMINOLOGIES
NON-VOLATILE RAM
Non-Volatile Random Access Memory (NVRAM) is the general name used to describe any type of random access memory which does not lose its information when power is turned off. This is in contrast to the most common forms of random access memory today, DRAM and SRAM, which both require continual power in order to maintain their data. NVRAM is a subgroup of the more general class of non-volatile memory types, the difference being that NVRAM devices offer random access, like hard disks.
SPIN
In quantum mechanics, spin is a fundamental property of atomic nuclei, hadrons, and elementary particles. For particles with non-zero spin, spin direction (also called spin for short) is an important intrinsic degree of freedom.
As the name indicates, the spin has originally been thought of as a rotation of particles around their own axis. This picture is correct insofar as spins obey the same mathematical laws as do quantized angular momenta. On the other hand, spins have some peculiar properties that distinguish them from orbital angular momenta: spins may have half-integer quantum numbers, and the spin of charged particles is associated with a magnetic dipole moment in a way (g-factor different from 1) that is incompatible with classical physics.
The electron spin is the key to the Pauli Exclusion Principle and to the understanding of the periodic system of chemical elements. Spin-orbit coupling leads to the fine structure of atomic spectra, which is used in atomic clocks and in the modern definition of the fundamental unit second. Precise measurements of the g-factor of the electron have played an important role in the development and verification of quantum electrodynamics. Electron spins play an important role in magnetism, with applications for instance in computer memories. Manipulation of spins in semiconductor devices is the subject of the developing field of spintronics. The manipulation of nuclear spins by radiofrequency waves (nuclear magnetic resonance) is important in chemical spectroscopy and medical imaging. The photon spin is associated with the polarization of light.
The head-on collision of a quark (red ball) from one proton (orange ball) with a gluon (green ball) from another proton with opposite spin, spin is represented by the blue arrows circling the protons and the quark. The blue question marks circling the gluon represent the question: Are gluons polarized? Ejected from the collision are a shower of quarks and a photon of light (purple ball).
SPIN
Particles with spin can possess a magnetic dipole moment, just like a rotating electrically charged body in classical electrodynamics. These magnetic moments can be experimentally observed in several ways, e.g. by the deflection of particles by inhomogeneous magnetic fields in a Stern-Gerlach experiment, or by measuring the magnetic fields generated by the particles themselves. The intrinsic magnetic moment p of an elementary particle with charge q, mass m, and spin S, is
Where the dimensionless quantity g is called the g-factor. For exclusively orbital rotations it would be 1.
In ordinary materials, the magnetic dipole moments of individual atoms produce magnetic fields that cancel one another, because each dipole points in a random direction. Ferromagnetic materials below their Curie temperature, however, exhibit magnetic domains in which the atomic dipole moments are locally aligned, producing a macroscopic, non-zero magnetic field from the domain. These are the ordinary "magnets" with which we are all familiar.
The study of the behavior of such "spin models" is a thriving area of research in condensed matter physics. For instance, the Ising model describes spins (dipoles) that have only two possible states, up and down, whereas in the Heisenberg model the spin vector is allowed to point in any direction. These models have many interesting properties, which have led to interesting results in the theory of phase transitions.
SPIN TRANSFER
Spin transfer is the phenomenon in which the spin angular momentum of the charge carriers (usually electrons) gets transferred from one location to another. This phenomenon is responsible for several important and observable physical effects.
Most famously, spin polarized current passing into a nanoscale magnet tends to deposit some of its spin angular momentum into the magnet, thereby applying a large torque to the magnetization. This enables magnetic manipulations far more efficiently than can be achieved with magnetic fields alone, especially as device applications shrink in scale. In the hard disk industry, where a series of nanoscale magnetic layers called a spin valve is often used to measure the small local magnetic fields above the disk surface, this is an undesirable effect, as it hinders the ability to measure the state of the valve without disturbing it. In the MRAM industry, however, this effect may prove incredibly useful in reducing power consumption.
INTRODUCTION
SPINTRONICS:
Spintronics (a neologism meaning "spin transport electronics"), also known as magneto electronics, is an emerging technology which exploits the intrinsic spin of electrons and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-state devices.
Electrons are spin-1/2 fermions and therefore constitute a two-state system with spin "up" and spin "down". To make a spintronic device, the primary requirements are to have a system that can generate a current of spin polarized electrons comprising more of one spin species - up or down - than the other (called a spin injector), and a separate system that is sensitive to the spin polarization of the electrons (spin detector). Manipulation of the electron spin during transport between injector and detector (especially in semiconductors) via spin precession can be accomplished using real external magnetic fields or effective fields caused by spin-orbit interaction.
Spin polarization in non-magnetic materials can be achieved either through the Zeeman Effect in large magnetic fields and low temperatures, or by non-equilibrium methods. In the latter case, the non-equilibrium polarization will decay over a timescale called the "spin lifetime". Spin lifetimes of conduction electrons in metals are relatively short (typically less than 1 nanosecond) but in semiconductors the lifetimes can be very long (microseconds at low temperatures), especially when the electrons are isolated in local trapping potentials (for instance, at impurities, where lifetimes can be milliseconds).
Metals-based spintronic devices
The simplest method of generating a spin-polarized current in a metal is to pass the current through a ferromagnetic material. The most common application of this effect is a Giant Magneto Resistance (GMR) device. A typical GMR device consists of at least two layers of ferromagnetic materials separated by a spacer layer. When the two magnetization vectors of the ferromagnetic layers are aligned, the electrical resistance will be lower (so a higher current flows at constant voltage) than if the ferromagnetic layers are anti-aligned. This constitutes a magnetic field sensor. Two variants of GMR have been applied in devices:
• Current-In-Plane (CIP), where the electric current flows parallel to the layers.
• Current-Perpendicular-to-Plane (CPP), where the electric current flows in a direction perpendicular to the layers.
Other metals-based spintronics devices:
• Tunnel Magneto Resistance (TMR), where CPP transport is achieved by using quantum- mechanical tunneling of electrons through a thin insulator separating ferromagnetic layers.
• Spin Torque Transfer, where a current of spin-polarized electrons is used to control the magnetization direction of ferromagnetic electrodes in the device.
The storage density of hard drives is rapidly increasing along an exponential growth curve, in part because spintronics-enabled devices like GMR and TMR sensors have increased the sensitivity of the read head which measures the magnetic state of small magnetic domains (bits) on the spinning platter. The doubling period for the areal density of information storage is twelve months, much shorter than Moore's Law, which observes that the
number of transistors that can cheaply be incorporated in an integrated circuit doubles every two years.
MRAM, or magnetic random access memory, uses arrays of TMR or Spin torque transfer devices. MRAM is nonvolatile (unlike charge-based DRAM in today's computers) so information is stored even when power is turned off, potentially providing instant-on computing. Motorola has developed a 256 kb MRAM based on a single magnetic tunnel junction and a single transistor. This MRAM has a read/write cycle of fewer than 50 nanoseconds. Another design in development, called Racetrack memory, encodes information in the direction of magnetization between domain walls of a ferromagnetic metal wire.
Semiconductor-based spintronic devices
In early efforts, spin-polarized electrons are generated via optical orientation using circularly-polarized photons at the band gap energy incident on semiconductors with appreciable spin-orbit interaction (like GaAs and ZnSe). Although electrical spin injection can be achieved in metallic systems by simply passing a current through a ferromagnet, the large impedance mismatch between ferromagnetic metals and semiconductors prevented efficient injection across metal-semiconductor interfaces. A solution to this problem is to use ferromagnetic semiconductor sources (like manganese-doped gallium arsenide GaMnAs), increasing the interface resistance with a tunnel barrier, or using hot-electron injection.