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 (VT) 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.