Independently-controlled-Gate FinFET Schmitt Trigger sub-threshold SRAMs

We propose three novel Independently-controlled-Gate Schmitt Trigger (IG_ST) FinFET SRAM cells for sub-threshold operation. The proposed IG ST 8T SRAM cells utilize split-gate FinFET devices to provide built-in feedback mechanism for Schmitt Trigger action. 3D mixed-mode simulations are used to evaluate the RSNM, WSNM, HSNM, and Standby leakage of proposed cells. The proposed cells demonstrate 1.81X and 2.11X higher nominal RSNM at V_CS=0.4V and 0.15V, respectively. The cell AC performance are evaluated, and shown to be adequate for the intended sub-threshold applications. Compared with previously reported 10T Schmitt Trigger sub-threshold SRAM cells, the proposed cells exhibit comparable or better RSNM, higher density, and lower Standby leakage current. 3D mixed-mode Monte Carlo simulations are performed to investigate the impacts of process variations (L_eff and W_fin) and random variations (Gate LER and Fin LER) on RSNM. Our results indicate that even at the worst corner, two of the proposed cells can provide sufficient margin of μ/σ ratio=7. With enhanced cell stability, reduced cell area and Standby leakage, adequate performance, and robust tolerance to process variations and random variations, these proposed cells are promising candidates for future ultra-low-voltage sub-threshold applications.