低電圧動作シリコン系　Ｂｅｙｏｎｄ　ＣＭＯＳデバイスの研究

这项研究提出了一种新的工作机制，即Vth自调节，可以在0.3V以下工作，甚至可以提高SRAM单元的稳定性。Vth自调整MOSFET在动态特性上表现出两种Vth态，而在静态特性上由于隧穿现象的滞后而表现出改善的通断电流比和S因数。动态特性中的Vth漂移可用于提高SRAM单元的稳定性。此外，改进的通断电流比和S因数适用于低电压运行。然而，由于垂直尺寸的限制，平面结构的Vth自调整MOSFET显示出关键的短沟效应。因此，在Vth自调整MOSFET中引入了栅通绕(GAA)纳米线结构，从而对短沟效应具有很强的免疫力。为了增强Vth的自调节特性，通过扩大动态特性和静态特性的体因子差，对GaA纳米线结构进行了改进。因此，Vth漂移和S因子的改进变得更加重要。此外，还成功地制作了具有浮栅的三栅纳米线MOSFET，并显示出优异的器件性能。最后，即使在超低Vdd的情况下，它们也表现出Vth自调节特性，并通过仿真将这些结果重组为6个晶体管(6T)SRAM单元。具有Vth自调节功能的6T SRAM单元在Vdd=0.1V时表现出明显的稳定性改善。

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.