In the lecture, Kayvon mentioned that the 3D stack memory is connected to the processor (GPU/CPU/Soc Die in the diagram) via silicon, which makes it faster than using interconnect. What is the property of silicon that makes it transfer the data faster than interconnect?

Just to site the AMD website which defines HBM and mentions a lot of details mentioned in this slide- https://www.amd.com/en/technologies/hbm