it might be a beginner question, but why is there a 3.3V nfet, but no 3.3V pfet?

It's a good question. the 3.3V nfet is a native implant (close to zero Vth) transistor. From the skywater docs: _"The only differences between the sky130_fd_pr__nfet_03v3_nvt and sky130_fd_pr__nfet_05v0_nvt devices are the minimum gate length and the VDS requirements"._ *so this is basically a 5V oxide transistor, with some reduced length allowed*_._

@Stefan Schippers: I'm not sure that's the answer being sought, though. It's true that the only device that has "3v3" in the name is the zero-threshold device. But the devices intended to be used as 3.3V devices are

sky130_fd_pr__nfet_g5v0d10v5

and

sky130_fd_pr__pfet_g5v0d10v5

. The thick oxide devices can take up to 5V on the gate (hence the name), but they are regularly used in 3.3V applications.