(I'm an HCI PhD student at Stanford.)
Do you want to work on Project Soli at ATAP? Which part, the actual hardware / Radio antenna design? Then a PhD in analog design might be required to be qualified. Do you want to do the signal interpretation / analysis to detect gestures? Maybe a strong background in signals, filtering or even machine learning may be required.
HCI work can involve a lot of specific specialization which often requires these research / industry giants to demand a strong testament of your qualifications. Although not required, a PhD is often an easy way for them to see that.
If it is the more 'high-level' stuff, I'm not sure, as sometime a 'PhD in HCI' itself may be required (although I don't know too much what a 'PhD in HCI' entails)
Source: Experiences with HCI PhD's at UC Berkeley
I had one class in it. I didn't mind it but I didn't love it either.
Although I would love the opportunity to work at Microsoft Research, I accepted the fact that I likely never would.
Lately, I've been considering to join and/or create a distributed research team. The most challenging part has been to find people whose vision align with mine.
Feel free to contact me if that's of interest to you.
You can email me at aethjgore@gmail.com with your vision. I saw your other post re: the singular app / OS that does everything. I've been working on that and would love to have another person onboard.