Characterization of Single Event Cell Upsets in a Radiation Hardened SRAM in a 40 nm Bulk CMOS Technology

Abstract

A large amount of data needs to be stored in integrated circuits when data are being processed. The integrated circuits contain a large amount of static random access memory (SRAM) due to its high level of integration and speed. SRAM units should be as small as possible to achieve higher storage density. In this work, the features of single cell upsets (SCUs) and multiple cell upsets (MCUs) in a full custom SRAM are tested for a 40 nm bulk CMOS technology node, and Ge (linear energy transfer (LET) = 37.3 MeV cm2/mg), Cl (LET = 13.1 MeV cm2/mg), Al (LET = 8.6 MeV cm2/mg), O (LET = 3.1 MeV cm2/mg), and Li (LET = 0.5 MeV cm2/mg) particles are used. The test results show that the total single cell upset events are 2,000,147, 1,124,269, 413,100, 311,311, and 47,815 under the irradiation of Ge, Cl, Al, O, and Li, respectively. Moreover, due to single event upset reversal mechanism, multiple cell upsets significantly decrease. The total multiple cell upset events are 10, 4, 0, 0, and 0 under the irradiation of Ge, Cl, Al, O, and Li, respectively. There are a lot of single cell upsets appearing under Ge, Cl, Al, O, and Li exposure. The number is increasing with increasing LET, which means that well contacts still need optimization in the full custom SRAM. Close spacing of well contacts or increasing contacts are the approaches used to drain the excess carriers quickly, and error detection and correction (EDAC) is used for SRAM technology. The features show that SCUs have become a major source of soft errors for the full custom SRAM. Combining close spacing of well contacts with error detection and correction (EDAC) and a well engineering scheme are used to reduce single cell upsets, although there are a few MCUs which are inevitable. Radiation hardened by design schemes needs to be further improved.