Impact of Random Variations on Cell Stability and Write-Ability of Low-Voltage SRAMs Using Monolayer and Bilayer Transition Metal Dichalcogenide (TMD) MOSFETs

This letter evaluates and analyzes the impacts of random variations on cell stability and write-ability of low-voltage SRAMs using monolayer and bilayer transition metal dichalcogenide (TMD) devices based on ITRS 2028 (5.9 nm) node with the aid of atomistic TCAD mixed-mode simulations. Our study indicates that, for 6T SRAM, the monolayer/bilayer TMD devices may fail to provide the 6σ yield requirement for read static noise margin (RSNM) due to severe metal-gate work function variation in spite of their excellent electrostatics, and hence circuit techniques, such as bootstrapped dynamic power rails or the standard 8T cell, are needed. Besides, R_SD as a major concern of TMDs should be less of an issue for near-/sub-threshold SRAMs for ultra low-power applications. For the standard 8T cell structure, the RSNMs of both monolayer and bilayer 8T SRAMs improve significantly, and the bilayer 8T SRAM exhibits better write static noise margin (WSNM). In addition, write-assist techniques (including negative bit-line, boosted word-line, and lower cell supply) for improving WSNM are examined and shown to be more effective for monolayer 8T SRAMs than the bilayer counterparts.