Radiation tolerant capacitor-SRAM without area overhead

Abstract

In memory semiconductors such as a static random access memory (SRAM), a common problem is soft errors under radiation environment. These soft errors cause bit flips, which are referred to as single event upsets (SEUs). Some radiation-hardened SRAM cells such as a Quatro SRAM, we-Quatro SRAM, and DICE SRAM cells have been reported for years. However, these designs have the disadvantage of taking up more area than a conventional 6T SRAM cell. Thus, we propose a radiation-hardened SRAM cell design that we named capacitor-static random access memory (C-SRAM) without area overhead. The C-SRAM is formed by simply adding a capacitor to the conventional 6T SRAM. It was designed to mitigate the radiation effect using the conservation law of electrical charge. Moreover, it has the same cell size as the conventional 6T SRAM cell. Its static noise margins (SNMs), which are indicators of operational stability, are equal to the conventional 6T SRAM values of 530 mV, 220 mV, and 860 mV in hold, read, and write modes, respectively. The results of the SEU simulation test showed that it had 4.761 times better flipping tolerance than the conventional 6T SRAM with a charge value of 247.494 fC. In addition, irradiation experiments also confirmed that the C-SRAM cell was more tolerant than the 6T SRAM cell. The conventional 6T SRAM and C-SRAM were fabricated using a standard 0.18 μm CMOS process.

Keywords

• C-SRAM
• Radiation-hardened SRAM cell
• Radiation tolerance
• Single event upset
• Soft error
• Static noise margin