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What is a dummy in analog layout?

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Advanced Member level 4
Jan 3, 2005
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i always see dummy in analog layout. Can someone tell me what is dummy and why we need to use it?

I usually see the dummy will place at the two end of the transistor, that's why?

Thanks for your help.

Re: what is dummy?

poly resistors are created by etching a doped poly film.The etching rate depends on the geometry of the poly openings. Larger openings grant more access to the etchant and thus clear more quickly than small openings. The edges of the resistors facing outward form the sidewalls of a vast opening that etches quickly and clears early. The edges of the resistors facing inward form sidewalls of narrow slits that etch more slowly and clear later. The middle resistors lacks outward facing edges. so the final width of resistor is less than the expected. So we use Dummy resistors on two corners so that corner resistor segments have same etch rate as middle segments.
Re: what is dummy?

For device matchng...

Dummy will create a similar environment in both symmetry.....

Done to improve the functionality

what is dummy?

Dummy in sense of bonus cells.... that are layers that doped into the layout with NO layout functionality to the layout. Its used to improve the yield during fabrication , improves reliability of the chip.

Re: what is dummy?

A dummy element has no electrical connectivity with the rest of the layout elements.
helps in matching.

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