shared contacted diffusion in layout

[anhnha]

I am confused about shared contacted diffusion in CMOS layout.
Is it possible to use shared contacted diffusion for two nMOS transistors with different widths?
BTW, two nMOS and pMOS transistors are never shared contacted diffusion, right?

 

[erikl]

... shared contacted diffusion in CMOS layout.

Do you think e.g. of the "shared contacts" of the p+ substrate contact and the n+ source contact of an NMOSFET?
Or shared contacts of 2 MOSFET sources in parallel? Or shared contacts of 2 MOSFET drains in parallel? Or of drain and source of 2 serial MOSFETs?

Is it possible to use shared contacted diffusion for two nMOS transistors with different widths?

Depends on which sharing you think of. Pls. clarify.

BTW, two nMOS and pMOS transistors are never shared contacted diffusion, right?

Right.

 

[anhnha]

Thank you.

Or shared contacts of 2 MOSFET sources in parallel? Or shared contacts of 2 MOSFET drains in parallel? Or of drain and source of 2 serial MOSFETs?

Yes, I meant exactly one of three cases.
Can we share contacts in each case?

Depends on which sharing you think of. Pls. clarify.

As above.

 

[erikl]

Can we share contacts in each case?

Thinking again, yes, it's possible for each case. Several PDK's design rules, however, don't allow sharing substrate and source contacts.

 

[anhnha]

Thank you. To be 100% sure, could you confirm this?

 

[erikl]

Thank you. To be 100% sure, could you confirm this?

Cases 2b. and 3. only conditionally, if they all are in the same n-well (which means body control dependence, larger Vt depending on their source potential of M1 & M5). If they are in different n-wells, drain and sources cannot be shared, of course.

All other cases are correctly described.