Optimum Reliability Sizing for Complementary Metal Oxide Semiconductor Gates

Introducing redundancy at the device-level has been proposed as the most effective way to improve reliability. With the remarkable reliability of the complementary metal oxide semiconductor (CMOS) transistors the semiconductor industry was able to fabricate, the research on device-level redundancy has reduced. However, the increasing sensitivity to noise and variations (due to the massive scaling) of the CMOS transistors has led to a revival of interest in device-level redundancy schemes during the last decade. In this paper, we introduce a novel transistor sizing method that can be used to significantly reduce the probability of failure of CMOS gates due to threshold voltage variations. The method has almost no impact on the occupied area. For a given reliability target, the proposed sizing method provides very large scale integration (VLSI) designers with several transistor sizing options which allow them to optimize the trade-off between reliability and the traditional power-area-delay design parameters. The simulation results reported in this paper will show that the proposed transistor sizing method can improve the reliabilities of classical INV, NAND-2, and NOR-2 CMOS gates by factors of more than 10⁵, 10, and 10¹⁰ respectively, while the area is increased by less than 50%.