Future Design Direction for SRAM Data Array: Hierarchical Subarray With Active Interconnect

In sub 10 nm nodes, the growing dominance of interconnects in chips poses challenges in designing large-size static random-access memory (SRAM) subarrays. The main issue is the write failure problem arising from the increased resistance and capacitance for bitline (BL) and wordline (WL). To tackle this issue, the SRAM subarray design incorporates conventional (Conv.) divided WL and divided BL techniques based on 14-Å-compatible (A14) nanosheet (NS) technology. This approach allows for various subarray sizes with successful write operations, resulting in improved subarray-level performance and power (PP). However, the additional logic gates come with an area penalty that may degrade the overall performance, power, and area (PPA) at the macro level due to increased inter-subarray interconnect overhead. To overcome this limitation, the active interconnect (AIC) design is proposed with the features of fabricating another or multiple active regions at the back-end of line (BEOL) layers. By moving these extra logic gates from front-end of line to BEOL in the AIC divided subarray design, the area penalty is significantly mitigated without compromising PP compared to the standard (Std.) and Conv. divided counterparts. To achieve this concept, carbon nanotube gate-all-around transistor is explored as potential BEOL-compatible device. In this research, a comprehensive design-technology co-optimization analysis is conducted to verify the value and potential benefits of up to 65% macro-level energy-delay-area product improvement by AIC divided subarray design compared to the Std. subarray design.