I think that you can just define a conductive P+ substrate layer on top of the conductive substrate. You may need to define a fake metal layer to make a contact through the P+ layer down to the top of the substrate. You might be able to use a real thin perfect conductor for the fake metal, but the via through the P+ should have the same property as the P+ layer. The simulator should be able to solve for the changes in conductivity between the P+ and substrate layers around the fake metal contacts. Other folks may have better ideas than this.

I assume you are interested in the effective impedance between different ports for local contacts?

The bigger question is regarding how the bulk substrate is tied off to ground? If the substrate will be sitting on a grounded piece of metal then you might be able to assume the backside of the substrate is effectively tied to an ideal ground. If this is not the case (like in flip chip) then you may need to come up with a more realistic approach like putting real wide P+ substrate contacts fairly far away from the local ports to simulate substrate ties to ground through pad connections.

If the block you are putting these contacts in has a substrate guard ring then you need to include the ring too.

Hi,


actually now the problem is the "fake" metal layer is not making electrical contact with the substrate. I tried placing two such layers with about 10 um spacing, and ports on each one. The results came back as approximately a series RC instead of a parallel RC. I guess EMX cannot have metals making contact with "layers".

Does anybody know of any fix, or if this can be done with any other EM simulator?


thanks,
Aaron