TID Radiation Response of 3-D Vertical GAA SONOS Memory Cells

The total ionizing dose response against the γ ray of 3-D silicon-oxide-nitride-oxide-nitride (SONOS) cells with a vertical polysilicon channel was investigated. No leakage current increase or subthreshold slope degradation is observed up to the total ionizing dose of 1 Mrad(Si) even for devices scaled down to 22 nm, as the gate-all-around structure provides better control over the potential in the body, and shallow trench isolation oxide is not required. The threshold voltage (V_T) shifts trend during radiation is similar to the behavior of 2-D cells, and can be well predicted with McWhorter´s model. Benefiting from a larger initial memory window before irradiation, 3-D SONOS cells have a significant memory window of 4.5 V after exposure to a high radiation dose of 1 Mrad(Si). These results clearly indicate that 3-D SONOS devices are promising as radiation-tolerant memories.