You need a dual poly process and this is not that common,
it used to be a way to go in mixed signal CMOS but I think
people have moved to MIM caps as better Q and more
latitude in placement can be had (e.g. poly cap means
no CMOS structures coincide, while a higher-layers MIM
can be placed over active devices if planarity is good).
POP / PIP caps also have higher series resistance / lower
Q, and have higher parasitic C on the bottom plate owing
to proximity to the substrate plane.
... is using it in series possible?