Read Static Noise Margin Decrease of 65-nm 6-T SRAM Cell Induced by Total Ionizing Dose

Abstract

Read static noise margin (SNM) decrease of 65-nm 6-T cell induced by total ionizing dose (TID) was observed in this paper. The static random access memory (SRAM) cell test structure allowing precise measurement of read SNM was specifically designed and irradiated by gamma ray. Experimental results show that read SNM of 65-nm 6-T cell is sensitive to TID irradiation. The largest decrease of read SNM is 48 mV after 1000 krad(Si) irradiation, which is 36% of the value before TID irradiation. Being dependent on the measurement of radiation responses of cell transistors and simulation results, we conclude that the read SNM decrease is due to a threshold voltage shift induced by TID. Because narrow width transistors are employed in SRAM cells, threshold voltage of cell transistors will be shifted by charges trapped in shallow trench isolation, known as “Radiation-Induced Narrow Channel Effect.”