Spotted over at TechReport.com this morning and sourced from a post at 3dcenter.org, it appears that some additional information about the future Radeon R9 380X is starting to leak out through AMD employee LinkedIn pages.
Ilana Shternshain is a ASIC physical design engineer at AMD with more than 18 years of experience, 7-8 years of that with AMD. Under the background section is the line "Backend engineer and team leader at Intel and AMD, responsible for taping out state of the art products like Intel Pentium Processor with MMX technology and AMD R9 290X and 380X GPUs." A bit further down is an experience listing of the Playstation 4 APU as well as "AMD R9 380X GPUs (largest in “King of the hill” line of products)."
Interesting – though not entirely enlightening. More interesting were the details found on Linglan Zhang's LinkedIn page (since removed):
Developed the world’s first 300W 2.5D discrete GPU SOC using stacked die High Bandwidth Memory and silicon interposer.
Now we have something to work with! A 300 watt TDP would make the R9 380X more power hungry than the current R9 290X Hawaii GPU. High bandwidth memory likely implies memory located on the substrate of the GPU itself, similar to what exists on the Xbox One APU, though configurations could differ in considerable ways. A bit of research on the silicon interposer reveals it as an implementation method for 2.5D chips:
There are two classes of true 3D chips which are being developed today. The first is known as 2½D where a so-called silicon interposer is created. The interposer does not contain any active transistors, only interconnect (and perhaps decoupling capacitors), thus avoiding the issue of threshold shift mentioned above. The chips are attached to the interposer by flipping them so that the active chips do not require any TSVs to be created. True 3D chips have TSVs going through active chips and, in the future, have potential to be stacked several die high (first for low-power memories where the heat and power distribution issues are less critical).
An interposer would allow the GPU and stacked die memory to be built on different process technology, for example, but could also make the chips more fragile during final assembly. Obviously there a lot more questions than answers based on these rumors sourced from LinkedIn, but it's interesting to attempt to gauge where AMD is headed in its continued quest to take back market share from NVIDIA.