Electric Clock for NanoMagnet Logic Circuits - Field-Coupled Nanocomputing: Paradigms, Progress, and Perspectives - page 86

are bigger. See Sect. 2.4 for further details on performance. With a width of
just 3 magnets performance are improved but fabrication processes with higher
resolution are required. Smaller widths cannot be reached because the required
resolution cannot be achieved with current technological processes. Bigger values
of width are also not possible because bigger structures have far too many mag-
nets in the critical path, generating therefore errors in the signal propagation.

IN1 OUT1

IN2

OUT2

IN3

Fig. 13. Complex circuit layout example using the magnetoelastic clock.

Figure 13 shows a possible layout of a NML circuit based on this clock solu-
tion. Every piezoelectric island is equal to a clock zone. Particularly, the layout
is made by interleaved lines of clock zones to correctly match the outputs com-
ing from a clock zone with inputs of neighbor clock zones. Due to the presence
of electrodes, signals propagation follows the north and south border of every
clock zone. A clock zone then can be occupied by a logic gate or simply by a
wire. Finally, a proper multiphase clock scheme can be applied to the layout to
obtained a correct signals propagation.
The layout here proposed is based on mechanical isolated islands. To obtain
islands of PZT starting from a uniform substrate, it can be patterned through
lithography, selectively removing part of the piezoelectric material in a specific
area [ 38 , 39 ], as shown in Fig. 14 . PZT can be completely removed to obtain
perfect isolation, however also removing just a small part of it provides a very
good mechanical separation, so that the strain of an island does not produce
a strain in neighbor cells. This is an important requisite in every clock system:
When magnets of a specific zones are clocked there should be no crosstalk with
their neighbor clock zones. Clearly the higher the resolution of the lithography
process used is, the smallest the area that can be removed is. Theoretically, a
gap of few nanometers (providing to have a process with high enough resolution)
is sucient, since the strain of every island is smaller than 1 nm.