Question: why we use P_sub?

[mark_lhm]

Hello, I am a new. And I am a little puzzleed by this question
Can anybody tell me why the modern process chooseed P_sub.
And what is worry with N_sub?
Thank you very much!

 

[k_90]

the main reason behind using a p type substrate is that the cost of implementing an n type substrate as a default base is pretty higher than that of using a p type substrate

also process limitaions make it a little tough and not a very acurate option if we use an n type substrate

one one more point of view if we consider the physics of the n type substrate is, they tend to carry electrons as carriers which are more mobile than the holes ....to be precise somewhere around 3 times more mobile,

so if we are using an n type substrate, then subsrate noise could also become a major factor.

 

[BackerShu]

one one more point of view if we consider the physics of the n type substrate is, they tend to carry electrons as carriers which are more mobile than the holes ....to be precise somewhere around 3 times more mobile,

quote]

I think it may be a important reason.

 

[mark_lhm]

Of course, electrons is more mobile than the holes whatever in n type substrate or p type substrate.
If it is the reason, what is the different between make a PMOS in a Nwell under the P_sub condition and make a PMOS in the N_sub?