Study on Transient Ionizing Radiation Effect of 40nm SRAM

This paper investigates the core voltage's reduction of electronics induced by transient ionizing radiation and how it influences TREE (Transient Ionizing Radiation Effect of Electronics) on SRAM. 6T memory cell of 40nm SRAM was constructed in TCAD and the dose-rate upset threshold of it was 1.5×10¹¹Gy(Si)/s when working at nominal core voltage. However, the transient ionizing radiation experiment of 40nm SRAM carried out on “QiangGuang-I” accelerator indicated that the dose-rate upset threshold of the whole SRAM chip was1.0×10⁷ Gy(Si)/s. And the simulation results indicated that the reduction of memory cell's core voltage would reduce the dose-rate upset threshold significantly as the memory cell's SNM (Static Noise Margin) decreases with the reduction of memory cell's core voltage. As there is LDO (Low Dropout Regulator) inside SRAM for conversion of voltage from I/O to core, we also did the transient ionizing radiation experiment of LDO and the experimental results showed that the output voltage of LDO would decrease during transient ionizing radiation which verified the probability of the reduction of memory cell's core voltage during transient ionizing radiation. Combined with the experiment and simulation results, it can be assumed that the reduction of core voltage during radiation is a main reason causing SRAM upset.