This has been pretty clear about all Apple chip designs, going back to some of the first A series afaik. They are "unified memory" but not "memory on die", they've always been "memory on package"-- ie. the ram is packaged together with the CPU, often under a single heat spreader, but they are separate components.
Apple's own product shots have shown this. Here's a bunch of links that clearly show the memory as separate. Lots of these modules you can make out the serial or model numbers and look up the manufacturer of them from directly :)
