Re-Examination of Impact of Intrinsic Dopant Fluctuations on Static RAM (SRAM) Static Noise Margin

Abstract

The impacts of intrinsic threshold voltage (Vth) fluctuations in metal oxide semiconductor field effect transistors (MOSFETs) on the static random access memory (SRAM) static noise margin (SNM) are re-examined in the 90 nm to 45 nm technology generations on the basis of the 2003 International Technology Roadmap for Semiconductors (ITRS). The Vth fluctuations due to random dopant fluctuations are calculated using the cube model and the deviations in SNM are derived using two-dimensional device simulations and SPICE simulations. It is found that five sigma of SNM deviations is ensured at gate length Lg=53 nm in the 90 nm node at β=1.5. It is also demonstrated that, although four sigma of SNM deviations exceeds the average SNM in the 65 nm (Lg=32 nm) and 45 nm (Lg=22 nm) nodes, four sigma of SNM deviations is ensured by adjusting Lg, the power supply voltage (Vdd), Vth and the drain-induced barrier lowering (DIBL) without using improved MOSFET structures.