TSMC mimcap pcell question

[Brittoo]

Hello all

A mimcap pcell provided by TSMC has the cap in DNW (mimcap_woum). The Nwell and substrate tap guardring structures are tied together. In one of the designs using this mimcap, the guard ring was connected to substrate potential.

As per my understanding, there is no depletion region formed due to the absence of reverse bias . What is the benefit of connecting the DNW to the substrate potential :?:

Regards
Brittoo

 

[erikl]

As per my understanding, there is no depletion region formed due to the absence of reverse bias .

Due to the built-in voltage, there's still a (small) depletion region.

What is the benefit of connecting the DNW to the substrate potential :?:

One connection less. Actually, I don't know. May be they fear substrate noise coupling if the DNW comes close to the low-ohmic substrate, s. pp. 32, 46 & 50 of the PDF below.