| 研究実績の概要 |
This study suggests a new operation mechanism, Vth self-adjustment, for sub-0.3 V operation even enhancing stability of SRAM cells. Vth self-adjusting MOSFETs show two kinds of Vth states in dynamic characteristics, while they show improved on/off current ratio and S-factor in static characteristics by time-lag of tunneling phenomenon. The Vth shift in dynamic characteristics can be used for enhancing stability of SRAM cells. Furthermore, improved on/off current ratio and S-factor are suitable for low voltage operation. However, Vth self-adjusting MOSFETs with planar structure show crucial short channel effects due to limitation of vertical scaling. Thus, gate-all-around (GAA) nanowire structure is introduced to Vth self-adjusting MOSFETs for strong immunity to short channel effects. In order to enhance Vth self-adjusting characteristics, the GAA nanowire structure is modified through enlarged body factor difference between dynamic and static characteristics. Hence, Vth shift and S-factor improvement become enhanced. Also, tri-gate nanowire MOSFETs with floating gates are successfully fabricated and they show excellent device performance. Finally, they show Vth self-adjusting characteristics even in ultra-low Vdd and these results are recomposed to 6 transistors (6T) SRAM cells using simulation. The 6T SRAM cells with Vth self-adjustment clearly show stability improvement at Vdd = 0.1 V.
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