Wafer-on-Wafer (WOW) is a 3D integration technology developed by the the WOW Alliance, Japan.
Cross-sectional SEM pictures of a) WOW stack and b) ultra-thin DRAM wafer, respectively.
See also TSMC's WoW (Wafer-on-Wafer).
- T. Ohba, “Production-worthy WOW 3D integration technology using bumpless interconnects and ultra-thinning processes,” in 2016 IEEE Symposium on VLSI Technology, 2016, pp. 1–2. Available: http://dx.doi.org/10.1109/VLSIT.2016.7573427