Some doubts on lower technology layout

[vinodhsaminathan]

Hi,
1. why while making finger it is advisable to put source at the edge?
2. Avoid routing nodes of stacked devices - means what?
3. What is meant by device leg?
4. What is density rule?

 

[reidintransit]

Hi,
1. why while making finger it is advisable to put source at the edge?
easier to connect to power source at edge.
2. Avoid routing nodes of stacked devices - means what?
?
3. What is meant by device leg?
the wire or lead of a component. sometimes leads look like the legs of a bug.
4. What is density rule?
how many components can be in a given area. determined by solder oven capabilities. high density areas take longer to heat up/cool down.

see above remarks

 

[vinodhsaminathan]

Hi,
what is poly jumper? s it not advisable to use it ?

 

[reidintransit]

From another thread in his forum.
https://www.edaboard.com/threads/99909/
It was the first thing I read on Saints book IC MASK DESIGN that you use poly jumpers. But later I found out that poly line has very big resistance higher than M1 or M2 and I never used it. If oyu add the resistance of poly + the contact resistance then you have created a very high parasitic resistance in this small node. Also, as poly line is closer to the substrate pracitic capacitance is quite big.

Therefore I suggest never use poly jumpers on lines, unless you have run out of metals - in any case you can avoid this situation- or you don't care about the paracitics much.

 

[dick_freebird]

Re stacked devices - stacking for voltage division is
a common trick, especially in SOI. But this depends on
all of the stages acting in unison or the protection from
overvoltage will fail. Long routes can be a source of
transient imbalance and instability (particularly, the
"guard" devices need low AC-impedance gate drive to
not act quasi-inductive).

I do not like edge-fed fingers for anything that has
a lot of current. Prefer to drop down into the device
from above, multiple vias, to avoid debiasing and so on.
Particularly bad is when you bring S and D out the same
side.

Poly jumpers are very resistive in an unsilicided-poly
flow or where poly is selectively silicided and does
not hit the "field poly". You'd want to know what the
poly sheet resistance is, to know how concerned you
are. Poly can be handy, but it can also add significant
unmodeled delay to circuit branches.