The 3-D Computer: An Integrated Stack of WSI Wafers

If it could be said that a single goal has motivated the development of advanced electronic systems over the past thirty years, it would probably be the attainment of an ever higher processing capability per unit volume. From the vacuum tube through the transistor, to the microelectronic era, and through a multitude of accompanying advances in physical packaging, the drive has consistently been to increase the amount of functional capability that can be contained within a given physical envelope. In applications where limited space is a dominant design parameter, increase in compactness has been the primary motivating factor. In other circumstances, the increased processing speed, reduced power consumption, and higher reliability that accompany higher levels of integration have been the driving constraints. In virtually all instances, though, the end goal has been the same: increase the packaging density of the active electronic elements.