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The advantages of Snake-Shape MOS Transistor

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Junior Member level 2
Dec 5, 2012
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Dear all,
Recently, I've found a type of MOS Transistor characterized by snake-shape layout (pls refer to the figure attached),
Snake-Shape NMOS.png

one prominent advantage of this type of transistor is it makes the layout quite compact for very large ratio of L/W.
I just wonder, whether it has other advantages and its disvantages.


Looks much more like a silicided nplus diffusion resistor (below POLY1).

Every serpentine resistor -is- a field MOS device (just
poorly engineered, if at all). The "DIFF" (I'd presume this
is "active area" / "thin ox") is not continuous across the
folds and any "gate" between the serpentine folds is
field, not thin ox in this case - a field FET. I believe
the only function of the poly here is as a field plate
(probably to keep said parasitic FETs out of play).

This snake layout will have more parasitic capacitance than a common centroid or interdigitated layout.

dear dick,
I have no idea of what the "gate" between the serpentine folds actually is.
It seems this structure only increases the parasitic MOS/Cap just as ajay said.

You can make very long and narrow mosfet in this snake shape, but it has only sense if this mosfet is used as large value resistor - no matching, speed, etc. advantages over rectangular, ELT or diamond layout style.

I've used this style of layout for weak pull up/pull down transistors. That is about the only use for it.

Pcell does not have gate contact typically, you have to add it in your layout:)

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I've used this style of layout for weak pull up/pull down transistors. That is about the only use for it.

Pretty reasonable

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