What's the status of SONOS devices for MPW-3? are we allowed to use them or is there some restrictions based on the extra masks required etc

You are allowed to use them. It's just that nobody knows how. I have a complete design of an NVM SRAM array that could be reverse-engineered to figure out what the programming requirements are. Since that is proprietary IP that was not released with the open-source PDK, somebody with an NDA with SkyWater will need to do the reverse engineering. It is on my to-do list, but I'm rather swamped with higher priorities. An alternative is just to create a SONOS cell with external access to everything and figure it out from experimentation. There was a submission on MPW-one that did this; the one called "analog neural network", I think. It had a handful of SONOS cells to experiment with.

an alternative is just to create a SONOS cell with external access to everything and figure it out from experimentation

that was the plan 🙂

Great idea, then. Go for it.

cool. I'll just need to make sure I use the right pins I think, to deal with the high voltages