Why do we always use p-substrate?

[raghavathej]

In every circuit we always use p-substrate (even in CMOS fabrication twin-tub process and also while drawing layouts) ,
why dont we prefer n-substrate ?...
What is the disadvantage of using n-type semiconductor material?

 

[dick_freebird]

"Always" is untrue. Back in the day we had processes
with N-epi and P-well (giving you a nearly-decent
substrate NPN). What drives the choice, is something
I've never known.

Present day, everything I do starts with intrinsic silicon
in a thin film. So there's another !always for you.

 

[erikl]

What drives the choice, is something I've never known.

I'd guess this has a historical reason: before CMOS, there was a pure NMOS technology. May be Monsanto (then), Wacker & those were more specialized on P substrates / P-epi ?

 

[dick_freebird]

But the very first MOS integrated circuits, as I recall, were
PMOS?

 

[erikl]

Yeah, you're right. But after that came the NMOS chips, didn't they?