Seems 85% likely 20nm/A57/Maxwell, but in the interest of objectivity there's no size scale to go off comparing them in these two pictures (well, the HDMI ports for the Shield, but nothing on the Switch shot there). Someone less lazy than me could calculate the die size from the 3DS cart in the first page.
If the RAM modules are 10x15mm, then from the close-up photo it would seem that Switch's SoC is about 11x11mm, or 121mm². (Which is pretty much exactly the size of the original TX1, for reference).