Hi all. A basic question: What are the units of dimensions of the Width and Length of 1.8V NMOS FET (Cell Name: sky130_fd_pr__nfet_01v8) by default. I mean whether its micrometer or nanometer(nm). Thank you.

The SkyWater model files set an internal scalefactor of 1E-6, so all values passed for width and length to any device should be in units of microns (and areas are in units of microns squared). so "W=1" is a 1um wide device.