Hai
Why Pmos have metal gate why not nmos in tsmc28nm HPL Technology ?

I am guessing that if both pmos and nmos gates are used, you will need 2 different types of "metal".

as a result,

it could be more complicated to qualify/stabilize the process (e.g. more variables to control) ?

or cost maybe ?

in any case ... I am also curious to know ... what does the foundry say ?

The different vth is the reason I am suggesting two metal, i.e. If the foundry uses metal gates on both nmos and pmos ... AND want to keep vth the same, then they need two types of metal.

So why then ... Hmmnnn ...