Nikon has always been fairly closed mouth about exactly who makes their sensors, but it’s been standard knowledge that they are made by Sony. The rumor is that Nikon has started developing (and possibly manufacturing) their own sensors.
If this rumor is true, this would mark a departure for Nikon. The first clues to this popped up in marketing materiels, with the D3100 being labeled as having a “Nikon Developed” sensor. This clue was picked up on by photographer and instructor Thom Hogan, who was later able to confirm this via various contacts at Nikon. Sony did announced a few months ago they weren’t going to be producing full frame senors any more, so that could be part of what brought on this change by Nikon.
[via Nikon Rumors]