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    Via connections with source and drain

    why source connections will have two vias and drain connection with one via
    any answer other than cad of drain should be less than source

    •   Alt6th December 2017, 06:28

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    Re: Via connections with source and drain

    1. Source and drain regions have contacts, not vias.

    2. For submicron processes generally a minimum of 2 contacts (or vias) are required for each connection, for reliability reason. There are, however, exceptions for some small Standard Cells (e.g. a low drive inverter), if a second contact|via would require an area extension of the cell. Here reliability is traded for area saving.



    •   Alt6th December 2017, 12:54

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    Re: Via connections with source and drain

    I don't think this is a universal rule - fewer number of contacts in drain than in source of a MOSFET.
    Typically, the number of contacts is equal.

    I can think of several different reasons why making two contacts in source and one in drain would make a sense:

    1. two-finger transistor with shared source - so that source carries a double current than each of the drains.

    2. in some circuits, people try to minimize gate-drain capacitance, so having less number of contacts in drian leads to smaller gate-drain capacitance (if it is dominated by gate-to-contact capacitance).



    •   Alt7th December 2017, 07:41

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    Re: Via connections with source and drain

    thanks erikl and timof for your replies
    this was a interview question



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    Re: Via connections with source and drain

    This is an important background information (that this question is from an interview, and not from real life).
    At interviews, people often ask questions that are ill posed, or don't have a simple answer, or don't have a known answer at all - to see the candidate's response, reasoning, attitude, way of thinking...



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