They literally mean the wires aka the metal layers and vias. And they are referring to the fact that with a shrinking process technology, the switch speed goes up but signal propagation speed goes down.
Now that i am home i have finally time to think about it and read up about it , i think i understand all the factors now.
When the process gets smaller, the resistance of the "wires" increases but since high speed signals also propagate through it, skin effects also becomes a role. As does capacitive effects.
Mainly relative permittivity (dielectric constant) and to some extend permability are the issues. At least that is what i understand of it.
Long time ago we had at work some experiments with a time domain reflection meter and the principle behind it. That was all about the velocity factor. And that was dependent on the material surrounding the conductor. Also was all about matching impedance to prevent reflections.
Even at chip layouts, the impedance must be matched yes to prevent reflections ?
For reflections to occur, the wire must be way longer so that the propagation time of the signal is much longer than the rise time of the signal and the impedance is not matched.
An advantage of smaller process technology would be that the propagation time of the signal is shorter but at the same time the relative permittivity increases. And thus the propagation speed goes down as well. There goes the advantage out of the window again.
Because the relative permittivity increases, the coulombforce on the electrons increase. That would make for less easy passing on of the " charge" signal from electron to electron.
And there is something that is confusing me.
I always understood that electron do not really travel that fast through a material because of mainly scattering and other atomic forces.
Thus when a signal is applied with very short rise time, the passing of the charge (the signal wave front) goes with the velocity factor or signal propagation speed but the electrons move at a relative slow pace through the material. But the electrons are very good at passing on information.
I recently read about ballistic conduction where an electron can travel through a material without scattering. Without encountering resistance but also not being a super conductor.
It is just that at small sizes, the electron encounters less interaction from surrounding atoms. At least i think that is the case of everything influences everything when interacting.
Does my rambling make any sense at all ?
Facebook
Twitter