Synthesis and Utilization of Standard Cells Amenable to Gear Ratio of Gate-Metal Pitches for Improving Pin Accessibility

Traditionally, the synthesis of standard cells invariably assumes that the gear ratio (GR) between the gate poly pitch in the cells and the metal pitch of the first vertical metal layer (to be used for routing) over the gate poly is 1:1 for chip implementation. However, the scaling trend in sub-10nm node CMOS designs is that GR is changing from 1:1 to 3:2 or 4:3, which means the number and location of pin access points vary depending on the cell placement location, thereby causing hard-to-pin-access if the pin access points were aligned on the offtrack routing pattern. This work overcomes the pin inaccessibility problem caused by non-1:1 GR in chip implementation. Precisely, we propose a non-1:1 GR aware DTCO (design and technology co-optimization) flow to generate cells with pin patterns that are best suited to the implementation of target design. To this end, we propose two new tasks to be installed in our DTCO framework: (1) from the existing cells optimized for 1:1 GR, we relocate their pin patterns amenable to non-1:1 GR, so that a maximal pin accessibility should be achieved; (2) we incrementally update the pin patterns of the cell instances with routing failures due to pin inaccessibility in the course of the DTCO iterations to produce the cells with best fitted pin patterns to the implementation of target design. We formulate task 1 into a problem instance of dynamic programming to find an optimal solution of pin positions, considering design rule and access conflict constraints while we solve task 2 by devising an assessment function on the pin accessibility enhanced by pin pattern extension to find out the most suitable direction for the extension. In the meantime, through experiments with benchmark circuits, it is shown that our DTCO methodology optimizing pin patterns amenable to non-1:1 GR is able to produce chip implementations with on average 5.88x fewer routing failures at no additional wirelength, timing, and power cost.