guoluren said:Hi, I am designing a multilayer interdigitated capacitor in a BiCMOS process with 6 metal layers. This capacitor is mainly for decoupling purpose, but some variants are also used for RF purpose in millimeter-wave range. Targeting capacitance falls in the range of 50fF to 300fF roughly.
I have made layout with cadence and extract it with Calibre RC. I have made em simulations with ADS Momentum and Sonnet EM. The resulting capacitor between the two electrodes is very similar with Calibre and Momentum. But the result from Sonnet is about 20% lower. I think I have taken care of deembedding as well as subdividing thick metal enough in Sonnet. But the result remains. Could anybody give me some suggestions about this? Thank you!
guoluren said:In Sonnet, dielectric layers are independent from metal stack.
guoluren said:Thanks Timof. That's exactly what I need, although some illusions about extraction tools(even some 2D simulators)are blown.
volker_muehlhaus said:guoluren said:In Sonnet, dielectric layers are independent from metal stack.
Wait ... if you are using thick metal in Sonnet, this will change the effective metal to metal distance, compared to a thin metal stackup. With increasing metal thickness, the distance to the metal above will decrease.
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One detail where things could go wrong with capacitance calculation: By default, Sonnet checks one layer above and one layer below for mesh alignment. If you have more than one dielectric layer between the capacitor plates, you should go to Analysis > Advanced Subsectioning > Polygon Edge Checking and increase the value as needed. Incorrect mesh alignment with big subsections can lead to capacitance values which are smaller than expected.
timof said:guoluren said:Thanks Timof. That's exactly what I need, although some illusions about extraction tools(even some 2D simulators)are blown.
Would you like to have a reliable reference value for your capacitance (based on a random-walk solver)?
guoluren said:I'd like to have a more accurate reference. Could you lend some help?
guoluren said:You are right. I have considered this.
volker_muehlhaus said:guoluren said:You are right. I have considered this.
That's strange.
From my experience, the solvers agree well on the extracted capacitance for MIM, which is a pretty trivial analysis task. The only issues that I have seen are mistakes in the stack up and errors from mesh alignment.
guoluren said:I used both vertical and horizontal coupling, maybe that's where the difference is.
volker_muehlhaus said:guoluren said:You are right. I have considered this.
That's strange.
From my experience, the solvers agree well on the extracted capacitance for MIM, which is a pretty trivial analysis task. The only issues that I have seen are mistakes in the stack up and errors from mesh alignment.
timof said:Yes, this is called "ease of use".
volker_muehlhaus said:guoluren said:In Sonnet, dielectric layers are independent from metal stack.
Wait ... if you are using thick metal in Sonnet, this will change the effective metal to metal distance, compared to a thin metal stackup. With increasing metal thickness, the distance to the metal above will decrease.
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