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Calculating Resistance and Metal width for Power MOS

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raju.hirematt

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Hi,
I want to calculate resistance of the power mos and also width of the metal layer used for power routing. Let say, my mos transistor has L=0.3u, W=50u and M=150 and I fingered it and made width of 10u. In this case how can I calculate the total resistance of the MOS and also power routing metal layer (so that I should not get any EM and IR drop).

Thanks in advance,
Raj
 

Well, of course you will get -some- I*R drop.

I have found interconnect to be as much as half the
total, in doing 100mOhm IC pass-FETs - with thick
metal, even.

You have to do it bottoms-up, I've just used Excel and
serial squares, parallel stipes, etc. to get the totals.
Lots of measuring and manual entry. Don't forget the
vias (tungsten plugs are very resistive and also a
bad electromigration-ratings hit).
 
The more detailed you make the simulation (you should simulate this) the more accurate your resistance calculation. Metal 1 resistance usually overwhelms all the other metal resistances because it is in narrow stripes on the drains and sources. One half of the MOSFET has all the metal 1 strapped with vias to metal 2, the other half is a long metal 1 strip. I usually simulate each strip as a metal 1 resistor, 50% of the length of the unstrapped side.

Don't forget bond wire resistance.
 
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