Back-gate pulse-controlled scheme for retention enhancement in double-gate nanosheet DRAM

Retention degradation in three-dimensional (3D) dynamic random-access memory (DRAM) becomes severe as access transistors adopt nanosheet structures. Using technology computer aided design simulations, the retention mechanisms of a double-gate nanosheet 1T1C DRAM are investigated under all four dynamic/static “1” and “0” conditions, revealing that the band-to-band tunneling-induced floating body effect (FBE) and quasi-static (QS) leakage dominate retention degradation in the 1 and 0 states, respectively. To exploit the independent controllability of the back-gate (BG), a state-dependent BG pulse-controlled scheme is proposed, in which a positive pulse is applied to suppress the FBE in the 1 states, while a negative pulse is used to suppress QS leakage in the 0 states, thereby enhancing retention under all conditions.