Just reading through the SW130 docs: https://skywater-pdk.readthedocs.io/en/main/rules/device-details.html The 1v8 standard vth devices are illustrated with a DNW under them. However the 1v8 low vth PMOS and NMOS have no DNW under them. Furthermore, the native devices are shown with a DNW under them. Is this really correct? Native devices sit in the substrate and low vth devices are simply standard vth devices with less doping. In other words, DNW should be below low vth devices but not native devices.

The standard nmos can be either in a p-well in DNW or p-well over substrate. The standard pmos requires a DNW (you can also check on the PCell layout). DNW is optional for both standard nmos and pmos Standard Vth devices have additional channel doping of the same type of the well. Low Vth devices have additional channel doping of opposite type of the well. Native devices have no channel doping. Note also low Vth devices has an additional metal layer

Thanks. Follow up questions are: 1. "Standard PMOS can be in a p-well over the substrate" ... how is the p-well isolated from the substrate? 2. "The standard pmos requires a DNW" ... the PMOS can exist without DNW underneath, for example if source and bulk are shorted, right? 3. "Native devices have no channel doping" ... so the native devices dont sit in the substrate? I havent downloaded the pdk yet, just want to get the details on the process before I commit to this. The context of my questions really are: I want DNW underneath all my devices (low vth or standard vth but dont really care about natives as I dont intend to use them). This process allows me to put DNW under PMOS/NMOS/low and standard vth right? Thanks

I corrected my previous answer DNW is optional for the standard devices 1. It is not. BTW in the quote you changed the original from nmos to pmos 2. You can place the pmos in an n-well over substrate. You need to define the n-well potential, no need for it to be tied to the source 3. Yes they sit in the substrate, channel doping is independent of well doping Sorry, I haven’t checked if you can put DNW under the lvt devices

Super. Thanks for that. Clears up all my questions.