Design of Gate-All-Around Silicon MOSFETs for 6-T SRAM Area Efficiency and Yield

Gate-all-around (GAA) MOSFETs relevant for the 11.9-nm CMOS technology node are optimized with device dimensions following the scale length rule. Variability in transistor performance due to systematic and random variations is estimated with the aid of TCAD 3-D device simulations, for these well-tempered GAA structures. The tradeoff between read stability and write-ability of 6-T static RAM cell designs implemented with GAA MOSFETs with either square or rectangular nanowire channel regions is then investigated, and a calibrated transistor I-V compact model is used to estimate cell yield. The results indicate that a rectangular (thin and wide) channel design achieves the optimal balance between the read yield and write yield and hence provides for the lowest minimum cell operating voltage, estimated to be ~0.45 V, as well as smaller cell area.