I was recently writing an article about an emerging technology for silicon die stacking — often referred to as 3D ICs. The promise is that instead of trying to squeeze everything onto a single die, you can use multiple dies. Each die may use a different fabrication technology optimized for that particular type of circuitry, such as memory, logic, analog, sensors etc. The dies are connected using Through Silicon Vias (TSVs), much the same as vias on a printed circuit board (PCB).

Most of the companies using this technology today have not yet combined the functional dies with TSVs. Instead they are using an interposer that acts just like a PCB. It performs the routing between the functional dies, but does not contain active components itself.

Full article here.