Difficulties extracting MIM capacitors

Hi Matthias,

I am having difficulties extracting double MIMN capacitors.
IO made a test case with an nmos, a resistor and a capacitor.

The nmos and resistor extract just fine, but the cap doesn't.

See the attached files with the gds, the script and the resulting netlist.



  • Hi Patrick,

    many thanks for this well-prepared test case.

    When looking at the layout and the extraction script, I'm fairly sure that via3 and metal4 are swapped and should be:

    via3        = input(35, 0)
    metal4      = input(36, 0)

    instead of 36 for via3 and 35 for metal4. If I change the script, I see a nice single cap extracted inside DMIM1pF with 0.98pF.

    Side note: I noticed that capacitance values are not shown in the netlist browser. This is because they are so small they are mistaken as zero. I'll fix that.

    Kind regards,


  • Thanks, This was a bonehead mistake.

    A few questions and comment I have about Klayout:
    1. Are there any examples of Pcells for devices such as MOS, Rs, Cs. I looked around some but have not found any yet
    2. It would be nice to be able tp control the format of the XY location display at the bottom, or have the option to match the snap grid
    3. The snap grid only affects drawing, The mouse does not snap to the grid in select mode, or just when moving around. Would be nice to have that option.

  • Very good ...

    Regarding your questions:
    1. I have not seen any CMOS device PCells for KLayout myself. As they are very PDK specific, I assume they are not openly distributed if they exist.
    2. That can be done - see https://github.com/KLayout/klayout/issues/963
    3. There actually is not grid for selection and the concept of grid isn't as simple as that. Every tool has it's own definition of grid/snapping/mouse coordinate translation. So the snapping is tool specific and the select tool simply does not have a grid. Hence there is no separate mouse cursor. I personally would find this annoying too, as I need a precise mouse positioning to select specific parts.


  • I agree that the precise mouse positioning makes it easier to select things. I think that in some case having the option to have the mouse snap to the current grid can be useful too.

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