10.3 Read Head in Magnetic Data Storage
235
ferromagnetic free layer leads to the enhancement of the output signal of the readhead.
NOTE: CPP and CIP Configuration
It is understandable that electric current is passing in two different ways through
magnetic super lattice structure. In one hand, current in plane (CIP) geometry
signifies current flowing along the layers where electrodes are locating on one
edge of the device structure. In other hand, current perpendicular to plane
(CPP) configuration implies current passing perpendicular to the layers where
the electrodes are positioning on different sides of the super lattice structure.
The results obtained in case of CPP geometry exhibits more than twice higher
value of GMR. However, in practice, CPP geometry is more complicated to
realize than CIP configuration. CPP and CIP are basically two different forms
of spin-valve sensors (Dieny et al. 1991).
Although in present days, spin-valve/GMR-based spintronics devices or
sensors CIP configuration is dominant, CPP configuration is expected to play a
major role in future terabit recording systems. CPP spin valve can be effectively
replaced by the magnetic tunnel junction (MTJ), in which current also passing
perpendicular to the plane of the layer. However, there is major difference in
the construction between a CPP spin valve and MTJ. As it is well known, MTJ
consists of two ferromagnetic layers separated by an insulating spacer layer,
instead of a metallic element. As a result, electrical conduction in MTJ takes
place through quantum–mechanical tunnelling. However, the large junction
resistance of MTJ, compared to that of CIP or CPP sensors, may possibly
affect its performance as a read sensor. This is due to the enhancement in
thermal noise and the reduction in bandwidth, arising out of the reduction in
junction size to a certain value.
10.4 Magnetic Random Access Memories (MRAM)
10.4.1 Application Based on Spin-Tunnel Junctions
Magnetoresistance values of Magnetic Tunnel Junctions, i.e., MTJ, ranging from 20
to 40% at room temperature, have initiated a new domain for technological applications (Parkin 1999; Koga et al. 2002; Ravi et al. 2014). In effect, MTJs, governed
by spin-dependent tunnelling phenomenon, can be implemented both as read head
sensors in hard disk drives for very high-density magnetic data storage and as nonvolatile memory cells in Magnetic Random Access Memories, i.e., MRAMs. Barrier
fabrication plays a critical role in the fabrication and operation of MTJ. In case of
read head applications, junction resistance should be less than 10 μm
2 . Concerning
235
ferromagnetic free layer leads to the enhancement of the output signal of the readhead.
NOTE: CPP and CIP Configuration
It is understandable that electric current is passing in two different ways through
magnetic super lattice structure. In one hand, current in plane (CIP) geometry
signifies current flowing along the layers where electrodes are locating on one
edge of the device structure. In other hand, current perpendicular to plane
(CPP) configuration implies current passing perpendicular to the layers where
the electrodes are positioning on different sides of the super lattice structure.
The results obtained in case of CPP geometry exhibits more than twice higher
value of GMR. However, in practice, CPP geometry is more complicated to
realize than CIP configuration. CPP and CIP are basically two different forms
of spin-valve sensors (Dieny et al. 1991).
Although in present days, spin-valve/GMR-based spintronics devices or
sensors CIP configuration is dominant, CPP configuration is expected to play a
major role in future terabit recording systems. CPP spin valve can be effectively
replaced by the magnetic tunnel junction (MTJ), in which current also passing
perpendicular to the plane of the layer. However, there is major difference in
the construction between a CPP spin valve and MTJ. As it is well known, MTJ
consists of two ferromagnetic layers separated by an insulating spacer layer,
instead of a metallic element. As a result, electrical conduction in MTJ takes
place through quantum–mechanical tunnelling. However, the large junction
resistance of MTJ, compared to that of CIP or CPP sensors, may possibly
affect its performance as a read sensor. This is due to the enhancement in
thermal noise and the reduction in bandwidth, arising out of the reduction in
junction size to a certain value.
10.4 Magnetic Random Access Memories (MRAM)
10.4.1 Application Based on Spin-Tunnel Junctions
Magnetoresistance values of Magnetic Tunnel Junctions, i.e., MTJ, ranging from 20
to 40% at room temperature, have initiated a new domain for technological applications (Parkin 1999; Koga et al. 2002; Ravi et al. 2014). In effect, MTJs, governed
by spin-dependent tunnelling phenomenon, can be implemented both as read head
sensors in hard disk drives for very high-density magnetic data storage and as nonvolatile memory cells in Magnetic Random Access Memories, i.e., MRAMs. Barrier
fabrication plays a critical role in the fabrication and operation of MTJ. In case of
read head applications, junction resistance should be less than 10 μm
2 . Concerning