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questions regarding the layout of the PMOS and NMOS transistor

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AdvaRes

AdvaRes

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Hi everybody,

The figure 1 shows the layout of a CMOS inverter.
I have 2 questions regarding the layout of the PMOS and NMOS transistor.


1/ Figure 3 Shows that in a PMOS transistor there is an N-Diffusion. Why this diffusion is not done in the Layout of the figure 1. Also for the NMOS the figure 3 Shows a P-diffusion that I can't see in the Layout of the figure1.


2/ When I see Figure 3 I conclude that NMOS and PMOS transitors are like shown in the figure 2. In fact, Figure 3 shows that in a NMOS transistor, the two region of N-Diff is separated by the substrate. In the layout of the figure 1 the two N-Diff are merged. Why ?

The same question is asked for the PMOS transistor.
 

Re: Layout question

ANSWERS：
1，the leftmost green region is the PMOS Ndiff region,it is connected with The source of PMOS and both are connected to VDD,the Ndiff is to provide a electrical connection to the Nwell.And so the Pdiff in the NMOS.
2.In the Drain and source formation step in fabrication,the Poly gate can be used to mask the channel region,and the dope can only be diffused or implanted in the unmasked sourec and drain region,the channel is masked and not influced,this is the self aligned process.
Hope these can helps!
if you find this is useful,plz press the help button!
 

    AdvaRes

    AdvaRes

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Re: Layout question

UR layout colours are not standard but even then ndiff in pmos is the ndiff_ntub tap
which is used to avoid the latchup and in the same way pdiff in nmos is the pdiff_sub tap for the nmos
 

    AdvaRes

    AdvaRes

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Re: Layout question

Hi,

Don't look at the figure 2, its not that clear.

and for the 1 st Q
U assume each contact is a separate region in FIG1 ( I assume u know what is contact) and then Green color is the n-diff ,white color is the p-diff & red color rectangle is the poly which is nothing but gate connection.
now considering all the above Definitions compare FIG1 and FIG3

i hope u understood....
 

    AdvaRes

    AdvaRes

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Re: Layout question

ravichandra said:
white color is the p-diff
i hope u understood....
Click to expand...

White color is the substrate and not the P-Diff.

That I'm trying to ask is that if you demand to draw the crossection of the Figure1 he will draw normaly the figure 2. And that is false since the correct answer is the figure 3 where we see N-Diff, P-Diff and the separation of the channel.

Could someone explain ?
 

Re: Layout question

If any one demands for a cross section of a nmos or a pmos if the layout contains the tap then the crosssection do contains the tap.
 

Re: Layout question

Hi,

which is figure 1 ???

if u see figures properly
the figure named FIG -3 is placed first

i am referring to the names given there
 

Re: Layout question

Advares, About your:
"""That I'm trying to ask is that if you demand to draw the crossection of the Figure1 he will draw normaly the figure 2. And that is false since the correct answer is the figure 3 where we see N-Diff, P-Diff and the separation of the channel."""



ANSWER: That could be perfectly caused by a mistake in the sideview creation skill code. I won't be surprised about that because I had some similar situation in the past...
 

    AdvaRes

    AdvaRes

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Re: Layout question

ravichandra said:
Hi,

which is figure 1 ???

if u see figures properly
the figure named FIG -3 is placed first

i am referring to the names given there
Click to expand...

I uploaded them by order but the Website shows them by decreasing order. I mean:
Figure1= FIG1
Figure2= FIG2
Figure3= FIG3
 

Re: Layout question

Hi ,
In Fig 1 it contains ndiff for pmos. and pdiif fot nmos . Its showing as attached one.

While in the actual layout you can make it as ditached so you can see the difference.

Regards,
Analayout.
 

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