Multiple-Cell Upset Analysis on 16/12-nm Bulk FinFET SRAM Caused by Proton Irradiation

The effects of proton-induced multiple-cell upsets (MCUs) on 16 and 12-nm fin field effect transistor (FinFET) static random access memories (SRAMs) were studied. Their dependence on the incident angle and supply voltage is discussed in terms of the MCU size and the fail-bit map (FBM). For perpendicular proton irradiation, we compared the MCU characteristics of FinFET SRAMs with 20-nm bulk planar SRAMs. In the proton energy dependence of single event upset (SEU) cross section, peak structures caused by proton direct ionization (PDI) were observed. At the nominal voltage condition, the peak was observed in the 20-nm bulk planar SRAM, but not in the 16 and 12-nm FinFET SRAMs. At the low voltage condition, however, the peak was observed even in the FinFET SRAMs. For the 16 and 12-nm FinFET SRAMs, the maximum size of MCUs was 3-bits, whereas that was 7-bits for 20-nm bulk planar SRAMs. Furthermore, the differences in the physical pattern of MCUs are observed between 16-nm FinFET and 20-nm SRAMs in perpendicular proton irradiation, where the 16-nm FinFET SRAM tends to have a rectangular shape with a longer side in the bitline (BL) direction. This clearly suggests that multiple-bit upsets (MBUs), which are known as uncorrectable MCUs, hardly occur in 16 and 12-nm FinFET SRAMs. For the angular irradiation, MBU probability in all MCU events reached 73% when tilting the SRAM at 75° across the fin body direction. However, the observed MBU size was up to 2-bits, indicating that bit-interleaves with more than 2-bits can be effective for mitigating MBUs in 16 and 12-nm FinFET SRAMs.