News Article
Spin Doctors
Researchers at Oxford University's Physics Department have developed an
improved version of their
Previous versions of the spin transistor were created by directly depositing
ferromagnetic and paramagnetic metal parts onto the doped silicon base
layer. This resulted in the formation of metal silicides at the interface,
creating a large depolarising effect on the flow of spin-polarised charge
carriers.
Additionally, the specific magnetic sensitivity of the device can be varied
over a wide range by adjusting the fabrication parameters. This allows the
device characteristics to be tailored to particular target magnetic field
strength ranges. The device therefore provides the benefits of a traditional
transistor (such as a large amplification factor) but with a current gain
dependent upon the local magnetic field.
The improved spin transistor device is the subject of a patent application
from Isis Innovation, Oxford University's technology transfer company. Spin
transistors have potential applications in magnetic field or position
sensors and non-volatile memory chips.
The original spin transistor, first described in 1993, exploits the presence
of two populations of charge carriers, solely distinguished by the direction
of their spin. In most semiconductor devices, such as transistors, the
relative proportions of the up and down carrier types are equal. By
introducing a ferromagnetic material as the carrier source, the up/down spin
ratio can be deliberately skewed in one direction. An intervening layer of
low coercivity paramagnetic material between the base and collector in
conjunction with an externally applied magnetic field can be used like a
magnetically variable valve to throttle the flow of electrons through the
device. After the electrons flow from the emitter electrode, the spin is
"analysed" by another layer of ferromagnetic material located at the surface
of the collector. Only electrons with the correct spin polarisation can
travel successfully through the device. This causes the device to behave
like a transistor whose electrical properties are magnetically tuneable.
ferromagnetic and paramagnetic metal parts onto the doped silicon base
layer. This resulted in the formation of metal silicides at the interface,
creating a large depolarising effect on the flow of spin-polarised charge
carriers.
Additionally, the specific magnetic sensitivity of the device can be varied
over a wide range by adjusting the fabrication parameters. This allows the
device characteristics to be tailored to particular target magnetic field
strength ranges. The device therefore provides the benefits of a traditional
transistor (such as a large amplification factor) but with a current gain
dependent upon the local magnetic field.
The improved spin transistor device is the subject of a patent application
from Isis Innovation, Oxford University's technology transfer company. Spin
transistors have potential applications in magnetic field or position
sensors and non-volatile memory chips.
The original spin transistor, first described in 1993, exploits the presence
of two populations of charge carriers, solely distinguished by the direction
of their spin. In most semiconductor devices, such as transistors, the
relative proportions of the up and down carrier types are equal. By
introducing a ferromagnetic material as the carrier source, the up/down spin
ratio can be deliberately skewed in one direction. An intervening layer of
low coercivity paramagnetic material between the base and collector in
conjunction with an externally applied magnetic field can be used like a
magnetically variable valve to throttle the flow of electrons through the
device. After the electrons flow from the emitter electrode, the spin is
"analysed" by another layer of ferromagnetic material located at the surface
of the collector. Only electrons with the correct spin polarisation can
travel successfully through the device. This causes the device to behave
like a transistor whose electrical properties are magnetically tuneable.