3D Nanomagnetic Logic
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information is propagating in z-direction without having vertically conductive channels nor magnetic material deposited for the via. Simply speaking, the field coupling
is generating a so called (virtual) magnetic via, transferring information from layer
1 to layer 2 and to layer 3.
It is important to mention, that magnet #1’ is not affected, as long as there is no
ANC fabricated. Please note the difference of magnets in the same layer to magnets
coupled with a magnetic via in vertical direction. The magnetization of magnets in
the same layer couples in anti-parallel manner and alignment happens in the following field-pulse (opposite direction), whereas the magnetization of vertically stacked
magnets are reversed within the same clocking pulse. Hence, for signal propagation
in vertical direction, a single clock-pulse is sufficient, but for logic operation with
neighboring magnets, a consecutive (opposite) field pulse is mandatory.
In order to estimate the field amplitudes of vertical coupling, Fig. 13a exemplarily
shows the calculated magnetic induction fields 40 nm above the crossection of a
magnetic island. At the position of the ANC (highlighted in light green), there are
coupling fields of strong amplitude acting in both z- and x-direction. They are oriented
in a way, that an ANC above the magnet can be easily reversed as described above.
There is another important aspect visible in this simple calculations, namely that
a precise (and optimized) position of the ANC is vital for correct operation, as
combined B x and B z fraction of amplitude massively influence the reversal field of
magnetization. At this point it becomes obvious, that the demands for fabrication
technology are high and a wisely chosen ANC position in the direction closer to the
origin, where the z-field is more constant turns out to be more robust.
4.2 Details on 3D NML Fabrication
A closer look at an employed fabrication technique for 3D stacked NML devices is
presented in Fig. 14. In principle, fabrication technology seems not to strongly differ
from the standard 2D layout of magnetic islands, however there are some details to
be considered:
• The seed layer is very important for magnetic thin-film growth, hence both
magnetic layer stacks should be grown on identical dielectric layers. Hydrogen
silsesquioxane (HSQ, [65]) has been found to be a promising material, as it can
be spun at low temperatures and at the same time planarizes the surface after
consecutive processing steps.
• Standard ANC fabrication is done at 50 kV acceleration voltage, depth control
of the straggling ions has to be considered in order to only pattern the top-most
magnetic layer.
• Alignment of four consecutive processing steps—(1) Co/Pt island patterning layer
1, (2) ANC formation layer 1, (3) Co/Pt island patterning layer 2, (4) ANC formation layer 2—is vital for device operation. It is hence beneficial to perform all
281
information is propagating in z-direction without having vertically conductive channels nor magnetic material deposited for the via. Simply speaking, the field coupling
is generating a so called (virtual) magnetic via, transferring information from layer
1 to layer 2 and to layer 3.
It is important to mention, that magnet #1’ is not affected, as long as there is no
ANC fabricated. Please note the difference of magnets in the same layer to magnets
coupled with a magnetic via in vertical direction. The magnetization of magnets in
the same layer couples in anti-parallel manner and alignment happens in the following field-pulse (opposite direction), whereas the magnetization of vertically stacked
magnets are reversed within the same clocking pulse. Hence, for signal propagation
in vertical direction, a single clock-pulse is sufficient, but for logic operation with
neighboring magnets, a consecutive (opposite) field pulse is mandatory.
In order to estimate the field amplitudes of vertical coupling, Fig. 13a exemplarily
shows the calculated magnetic induction fields 40 nm above the crossection of a
magnetic island. At the position of the ANC (highlighted in light green), there are
coupling fields of strong amplitude acting in both z- and x-direction. They are oriented
in a way, that an ANC above the magnet can be easily reversed as described above.
There is another important aspect visible in this simple calculations, namely that
a precise (and optimized) position of the ANC is vital for correct operation, as
combined B x and B z fraction of amplitude massively influence the reversal field of
magnetization. At this point it becomes obvious, that the demands for fabrication
technology are high and a wisely chosen ANC position in the direction closer to the
origin, where the z-field is more constant turns out to be more robust.
4.2 Details on 3D NML Fabrication
A closer look at an employed fabrication technique for 3D stacked NML devices is
presented in Fig. 14. In principle, fabrication technology seems not to strongly differ
from the standard 2D layout of magnetic islands, however there are some details to
be considered:
• The seed layer is very important for magnetic thin-film growth, hence both
magnetic layer stacks should be grown on identical dielectric layers. Hydrogen
silsesquioxane (HSQ, [65]) has been found to be a promising material, as it can
be spun at low temperatures and at the same time planarizes the surface after
consecutive processing steps.
• Standard ANC fabrication is done at 50 kV acceleration voltage, depth control
of the straggling ions has to be considered in order to only pattern the top-most
magnetic layer.
• Alignment of four consecutive processing steps—(1) Co/Pt island patterning layer
1, (2) ANC formation layer 1, (3) Co/Pt island patterning layer 2, (4) ANC formation layer 2—is vital for device operation. It is hence beneficial to perform all