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The advantages of Snake-Shape MOS Transistor

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abonic

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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
NMOS

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.

Thanks
 

erikl

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

dick_freebird

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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).
 

cmos_ajay

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

abonic

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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.
 

Dominik Przyborowski

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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.
 

rangermad

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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.
 

abonic

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

- - - Updated - - -

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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