A 4D device comprises a 2D multi-core logic and a 3D memory stack connected through the memory stack sidewall using a fine pitch T&J connection. The 3D memory in the stack is thinned from the original wafer thickness to no remaining Si. A tongue and groove device at the memory wafer top and bottom surfaces allows an accurate stack alignment. The memory stack also has micro-channels on the backside to allow fluid cooling. The memory stack is further diced at the fixed clock-cycle distance and is flipped on its side and re-assembled on to a template into a pseudo-wafer format. The top side wall of the assembly is polished and built with BEOL to fan-out and use the T&J fine pitch connection to join to the 2D logic wafer. The other side of the memory stack is polished, fanned-out, and bumped with C4 solder. The invention also comprises a process for manufacturing the device. In another aspect, the invention comprises a 4D process and device for over 50× greater than 2D memory density per die and an ultra high density memory.