Sony IEDM Presentation on 3-Layer Stacking Process Flow

Nikkei overviews Sony IEDM 2017 presentation on 3-layer stacked process flow for the fast image sensor presented at 2017 ISSCC:

The processing flow is:

The pixel, DRAM and logic wafers are manufactured using 90nm, 30nm and 40nm processes, respectively.
The DRAM wafer and the logic wafer are joined together, and the thickness of the DRAM wafer is reduced to 3μm
The DRAM and logic wafers are electrically connected with TSVs
The stacked wafers of the DRAM and logic are joined to the pixel wafer
The 3-layer wafer stack is thinned down to 130um and connected with TSVs

The numbers of TSVs connecting the pixel layer with DRAM is ~15,000 and DRAM with logic layer is ~20,000. Both of the TSVs have a diameter of 2.5μm and a pitch of 6.3μm. The 1/2.3-inch sensor has a resolution of 21.3MP and pixel size of 1.22um.