metal line width and running speed racing

[john7796]

Hi,

On metal line has 700um long, 0.25um width,

for 0.2fF/1um, the capacitance of the metal line is 0.2*700=140fF.

If the metal line need run up to 1GHz.

The peak current is V/R, R=t/5C=1ns/5*140fF=1.4k.

I=V/R=1.8/1.4K=1.28mA.

But the metal width is 0.25um=> only can run 250uA.

So the metal line width needs up to 1.28um to run 1.28mA.

However, the metal line capacitance is larger for lager width.

So the peak current needs more larger, this becomes to infinite loop.

Please help to solve this question. Thanks a lot.

John

 

[dick_freebird]

You should not confuse DC electromigration limits
with what a balanced, average=0, AC current can
be.

You also seem to consider only the line itself, and
not the driven load at the far end. This ought to
be significant and makes it not entirely a no-win.

But, running 700um at RF is not the best idea in
any case. You might do better to distribute your
amplifier (or logic) chain such that you have N
1/N*700um segments. Because each will have
a N times higher bandwidth, and while the system
may have more of a "brick wall" band-stop, that
wall will be much further out. Hopefully you'll end
up on the right side of it.