Independently-Controlled-Gate FinFET Schmitt Trigger Sub-threshold SRAMs

Abstract

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 [1] 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 mu/sigma 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.