Hi SG,
Now you're seeking the forbidden fruit of the Tree of Knowledge.
My serpentine explanation is that ordinary CMOS transistors are built up in layers parallel to the surface of the silicon wafer.
That is, the area of the gate, source, and drain of a field effect transistor (FET) are parallel to the surface, and the thickness is vertical to the surface.
As the density of the CMOS chips reached the limit of the technology (More's law about doubling the number of chips every couple of years), chip engineers needed to find new ways of increasing the number of transistors per wafer.
In a FINFET, the transistor is tipped on its side so the area is vertical to the surface, and the thickness occupies an area of the surface. Because the area is much larger than the thickness, this allows more transistors to be packed in.
Then we got "gate-all-around" (GAA) transistors which improved the performance of the transistors.
https://semiengineering.com/knowledge_centers/integrated-circuit/transistors/3d/gate-all-around-fet/
A
s the fin width in a finFET approaches 5nm, channel width variations could cause undesirable variability and mobility loss. One promising and futuristic transistor candidate — gate-all-around FET — could circumvent the problem. Considered the ultimate CMOS device in terms of electrostatics, gate-all-around is a device in which a gate is placed on all four sides of the channel. It’s basically a silicon nanowire with a gate going around it.
The comments refer to CFET, which is Complementary FET, a more complex GAA-FET.
https://semiengineering.com/knowledge_centers/integrated-circuit/transistors/3d/cfet/#:~:text=Slated for 2.5nm and beyond, complementary FET (CFET),the transistor stacks n-type wires on each other.
S
lated for 2.5nm and beyond, complementary FET (CFET) is a more complex version of a gate-all-around device. Traditional gate-all-around FETs stack several p-type wires on top of each other. In a separate device, the transistor stacks n-type wires on each other.
In CFETs, the idea is to stack both nFET and pFET wires on each other. A CFET could stack one nFET on top of a pFET wire, or two nFETs on top of two pFET wires. This ‘folding’ of the nFET and pFET eliminates the n-to-p separation bottleneck, reducing the cell active area footprint.
Since a CFET stacks both n- and p-type devices on each other, the transistor provides some benefits. The main benefit is area. In terms of electrostatic control, CFET would be the same as a normal nanowire. Both are gate-all-around architecture.
... and the research goes on ...