Ask HN: Getting into computer architecture design?

I've recently decided I'd like to get into computer architecture design, mainly to try and improve security at that level, to avoid dma attacks from attaching new hardware to your machine etc.

Where would be good to do a PhD in this area? Alternatively are there startups in this area that I could join with my skill set (below) and pick up the knowledge via osmosis. Is there another path that I am missing?

I've got a background in sysadmin-ing and coding my own research VMs, I know my logic gates/adders from school back in the day. To improve my skill set, I'm starting to learn Chisel and reading more computer architecture books.