Controlled placement of standard cell memory arrays for high density and low power in 28nm FD-SOI

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Abstract
Standard cell memories (SCMs) are becoming a popular alternative to SRAM IPs due to their design flexibility, ease of implementation, and robust operation at low supply voltages. Exclusively composed of standard cells, these memory arrays are implemented as part of the standard digital design flow. However, the synthesis and place and route (P&R) algorithms employed by this flow do not exploit the distinct and regular structure of an SCM array, leaving room for optimization. In this paper, we present a controlled placement design methodology for optimizing the physical implementation of SCM macros, leading to a structured, non-congested layout with close to 100% placement utilization and reduced wirelength as compared to unstructured layouts. Three sample SCM macro sizes were implemented according to the proposed methodology in a state-of-the-art 28nm FD-SOI technology, and compared with equivalent macros designed with the non-controlled, standard flow, achieving as much as a 22% reduction in area, a 57% reduction in switching power, and a 42% reduction in leakage power. In addition, these macros provide as much as an 88% reduction in switching power, as compared to equivalently sized, foundry provided SRAM IPs, while enabling robust functionality well below the minimum operating voltage of these IPs.