Three-Dimensional Design Methodologies for Tree-based FPGA Architecture by Vinod Pangracious Zied Marrakchi & Habib Mehrez

Author:Vinod Pangracious, Zied Marrakchi & Habib Mehrez
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

5.4 3D FPGA Interconnect Switch

The flexibility factor of a switch box refers to the number of wires to which each incoming wire can connect. Previous studies have shown that for a 2D FPGA, an of 3 provides good routability [34]. In such SBs, a track connects to one track on each of the other sides of SB. Disjoint and Universal topologies are examples of such SBs as illustrated in Fig. 5.8. In the case of island style Mesh-based FPGA, the 2D SBs are extended to 3D by adding two more faces, which contain terminal for vertical interconnection (Z direction), one for the layer above and another for the layer below as illustrated in Fig. 5.9. The channels in X and Y direction contain same number of tracks, however the channels in the Z direction differs from X and Y direction in its width, which is influenced by the via density provided by the 3D manufacturing technology. The length of channels in the Z direction depends on the wafer thickness as we discussed in Chap. 2, the wafer used in 3D integration will undergo thinning process and due to this the length of via can be much smaller than the average 2D wirelength, for example the wafer thickness of Tezzaron 3D manufacturing process is 12 , which includes 6 device layer (FEOL) and another 6 metal layer (BEOL) [35]. In effect, since the vertical vias will be fewer than horizontal wires, the two vertical faces will contain fewer terminal than the other four sides.

Fig. 5.103D Disjoint and disjoint-split switch box with channel in X=Y=4 an Z=2

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