10.7 Spin FET
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exhibits spin–orbit interaction. The origin of the spin–orbit interaction is the relativistic effect, and an electron feels the effective magnetic field B eff perpendicular to
its motion in the electric field E and propagation velocity direction v, such that B eff
∝ (v × E). A gate voltage can alter the spin–orbit interaction and is used to tune
the spin precession angle. The spin–orbit interaction is modified by the gate voltage
(the effective magnetic field is changed). Therefore, the spin precession angle can
be controlled by the gate voltage. In a spin FET, current flow is modified by the spin
precession angle.
The injection and detection of polarized spins with semiconducting channels is
complicated. Finally, Hyun Cheol Koo and colleagues working with Johnson demonstrated one version of the device in 2009 and then another version in 2015 where a
spin FET with the help of stray magnetic field induced by ferromagnetic patterns is
recommended. At source, the spin polarized electrons are generated by the Zeeman
splitting. The selected spins are sent out by the spin filtering effect at drain. This
device is frequently called a spin transistor, may be due to the fact that the gate
voltage changes its resistance from a high value (OFF) to a low value (ON), like
a real transistor. But a typical FET has an OFF/ON resistance ratio of about 10
5 .
By contrast, the spin transistor can at best reduce the current a little bit because the
strong randomization of spins can be taken place by scattering processes in solids
depending on the temperature and the channel length.
Alternative designs need to be implemented to overcome this constraint. Since
1990, researchers are looking for a device to replace the FET. But it seems more
practical to find ways to complement the FET. For example, small magnets are
unstable, making the resistance of an MTJ fluctuate with time. It has been argued
that such a stochastic MTJ could be combined with FETs to build a probabilistic
bit or a p-bit: a three-terminal device whose output alternates between ‘0’ and ‘1’
when the input is weak, but locks into ‘0’ for large negative input and to ‘1’ for large
positive input.
10.7.2 Advantages of Spin FET
Though the spin FET has not been realized yet but is regarded as one of the most
advanced applications of spintronics in the future. A spin FET would have several
advantages over a conventional FET: It could be used not only as a logic gate but
also as a non-volatile memory component. Less energy would be necessary to flip
an electron’s spin, and the spin could be flipped much faster than electrons can be
pushed away from their channel by a gate voltage. It may also be possible to change
the magnetization direction of the electrodes by applying a magnetic field.
255
exhibits spin–orbit interaction. The origin of the spin–orbit interaction is the relativistic effect, and an electron feels the effective magnetic field B eff perpendicular to
its motion in the electric field E and propagation velocity direction v, such that B eff
∝ (v × E). A gate voltage can alter the spin–orbit interaction and is used to tune
the spin precession angle. The spin–orbit interaction is modified by the gate voltage
(the effective magnetic field is changed). Therefore, the spin precession angle can
be controlled by the gate voltage. In a spin FET, current flow is modified by the spin
precession angle.
The injection and detection of polarized spins with semiconducting channels is
complicated. Finally, Hyun Cheol Koo and colleagues working with Johnson demonstrated one version of the device in 2009 and then another version in 2015 where a
spin FET with the help of stray magnetic field induced by ferromagnetic patterns is
recommended. At source, the spin polarized electrons are generated by the Zeeman
splitting. The selected spins are sent out by the spin filtering effect at drain. This
device is frequently called a spin transistor, may be due to the fact that the gate
voltage changes its resistance from a high value (OFF) to a low value (ON), like
a real transistor. But a typical FET has an OFF/ON resistance ratio of about 10
5 .
By contrast, the spin transistor can at best reduce the current a little bit because the
strong randomization of spins can be taken place by scattering processes in solids
depending on the temperature and the channel length.
Alternative designs need to be implemented to overcome this constraint. Since
1990, researchers are looking for a device to replace the FET. But it seems more
practical to find ways to complement the FET. For example, small magnets are
unstable, making the resistance of an MTJ fluctuate with time. It has been argued
that such a stochastic MTJ could be combined with FETs to build a probabilistic
bit or a p-bit: a three-terminal device whose output alternates between ‘0’ and ‘1’
when the input is weak, but locks into ‘0’ for large negative input and to ‘1’ for large
positive input.
10.7.2 Advantages of Spin FET
Though the spin FET has not been realized yet but is regarded as one of the most
advanced applications of spintronics in the future. A spin FET would have several
advantages over a conventional FET: It could be used not only as a logic gate but
also as a non-volatile memory component. Less energy would be necessary to flip
an electron’s spin, and the spin could be flipped much faster than electrons can be
pushed away from their channel by a gate voltage. It may also be possible to change
the magnetization direction of the electrodes by applying a magnetic field.