New MSU standard Cell Library: Cell Information

NEW MSU TEMPLATE FOR OVER THE CELL ROUTING IN THREE LAYER METAL

1. The cell height is 78 lambda (78U @ 2U technology / 46.8U @ 1.2U technology). This height was arrived at by allocating 23 lambda for P type devices, 17 lambda for N type devices, 10 lambda for metal1 rails and 18 lambda for intra-cell routing. The routing area allocated is not absolute. For different cells, there can be a variation in this parameter corresponding to the actual device widths. Fig. 1.

2. Power busses are 10 lambda wide in metal1 and run in the horizontal direction. The Vdd and Gnd terminals extend 2 lambda outside the cell structure.

3. The origin (reference point) of the cell is set to coincide with the Gnd terminal in the lower left corner of the cell.

4. Input/output terminals are of level Metal2 and are made double entry from top and bottom of the cell. Appropriate properties are attached to them in Led (Ex. TOP, BOTTOM, LEFT, RIGHT etc.). To connect between POLY and MET2 we have made use of POLY2MET2 contacts or MPOLY and M1M2 as appropriate. Care has been taken when adding terminals to POLY2MET2 contact. After connecting the Metal2 terminal it is made to touch the Metal2 portion of the POLY2MET2 contact. Fig. 2.

5. The distance between two input/output terminals (center to center) is atleast 8 lambda. The first/last possible terminal locations being atleast 4 lambda inside either edge of the cell. Fig. 3.

6. There are no specific routing channels that are defined in the template. All connections are made within the boundaries of the cell ( top edge of Gnd bus and bottom edge of the Vdd bus). Metal1 is largely used for horizontal routing (Ex. To connect between two poly's) and Metal2 for vertical routing (Ex. To connect P diffusion and N diffusion). Though the layout of Metal1 channels are flexible (i.e. horizontal or vertical), Metal2 channels are made vertical (inside the cell) whenever possible. That way it reduces blocking of incoming Metal2 channels (during routing between cells) that make connections to the I/O terminals. When possible Metal1 wires were used for vertical routing.

7. The Phillips style of layout is followed. It forms the baseline of this template. Made optimal use of the available space.

8. The bottom edge of the N diffusion aligns with the top edge of the Gnd bus. Similarly the top edge of the P diffusion aligns with the bottom edge of the Vdd bus. This results in sacrificing diffusion contact width but provides for more routing area. Where routing area is not of much concern, the diffusions have been positioned in such a manner which enables one to provide contacts that span the the maximum possible area of the diffusion. In any case there is no overlap of diffusion over the Metal1 power rails.

9. More substrate and well contacts have been placed whereever possible .

10. Reducing diffusion contact sizes typically increases the source/drain resistance. Since this affects the performance care has been taken to avoid this whenever possible.

11. To make connections between NDIFF and PDIFF contacts using Metal2 wires M1M2 contacts were used. Placing M1M2 contacts typically reduces the area available for routing. To provide for more routing area M1M2oPDiff and M1M2oNDiff contacts have been used as necessary. Fig. 4.

12. All cell geometry except the power rails have been confined to lie 2 lambda inside the vertical edges of the tesselation box.

The use of Metal3 enables the cells to be flipped over and placed on top of another cell resulting in a power bus width of 20 lambda. Besides it leads to possible elimination of channel space used for routing between cells, thus resulting in increased density.