Help me understand an interesting VCO layout

An interesting layout

I found a interesting layout, but I don't know why
It is the tail current lead of a VCO. The value of the current is very large.
see the attachment...
It uses tow layers of metal in parallel, and the width of the leads are wide enough to allow the big current. But I don't know why is there slots in the leads,and what is more interesting is that the slotted leads are not the same width but from wider to narrow.
What is the reason here?

An interesting layout

u may trace very branch to confirm why not equally divide current

Re: An interesting layout

In large (long wide) metal traces on an IC, there can be significant movement of the metal with high current densities. To prevent this metal moving about too much and destroying the passivation oxide layers around the metal, stress relief cut outs are employed. This allows an otherwise huge movement of a single metal line to be divided up into smnall components of movement along the track. These stress relief cut outs will be part of the design rule manual for a given technology and is determined by the Fab.
Failure to incorporate stress relief cut outs can lead to early failure of the part in its application. It may not happen immediately, but it will fail.
Most Fabs will either advise what cut outs to use, or will insert them themselves transparent to the designer.

An interesting layout

every wide metal (>10um @ 0.18uM) must sloted

Re: An interesting layout

I don't think it is stress relief cut otherwise they should cut evenly.
I suppose each wire goes to different transistors. These transistors should have different width also. The wire and transistors width are proportional to current flowing trough these transistors. I think it is done to equialize voltage drop across metal wires.

Re: An interesting layout

Fom said:

I don't think it is stress relief cut otherwise they should cut evenly.
I suppose each wire goes to different transistors. These transistors should have different width also. The wire and transistors width are proportional to current flowing trough these transistors. I think it is done to equialize voltage drop across metal wires.

Click to expand...

The slotted lead don't go to different transisitors. They converge at the end of the lead.The lead is very long by the way.

An interesting layout

do not be too paranoid, it most possibly just some random product of layout guy.

Re: An interesting layout

Definitely stress relief - even though it is not even, it is a function of contacts to active.

An interesting layout

I think the cuts are metal slot. But no idea why it's not cut evenly