# Total Ionizing Dose Effects in Advanced 28 nm Charge Trapping 3D NAND Flash Memory
## 3 Results and Discussions
Moreover, compared to the findings in [12; 21], this memory exhibits superior bit error rate performance. Figure 3: RBER under different bias states in AA patterns. (**a**) RBER in SLC mode. (**b**) RBER in TLC mode. Figure 2: RBER under different operating modes in AA patterns. (**a**) RBER in read-only state. (**b**) RBER in static state. (**c**) RBER during dynamic erase–program–read state. B. Standby current and read current  
Figure 5a reveals an increase in the standby current of 3D NAND Flash memory post-irradiation across different operating modes. The TLC mode, particularly in read-only mode, displays the most pronounced increase in standby current, especially when the radiation dose exceeds 20 krad (Si). Due to the out-of-tolerance standby current of flash memory after irradiation, we carried out an annealing test to study the effect of annealing time on the standby current of flash memory. In our work, the irradiated chips were placed at room temperature for two weeks and the standby current was measured every two days. The relationship between standby current and annealing time post-40 krad (Si) radiation is depicted in Figure 5b for the memory under TLC mode and read-only state. The figure demonstrates that as the annealing time extends, the standby current gradually diminishes and then  
Figure 4: Bit errors for different data patterns. (**a**) SLC mode, read-only. (**b**) SLC mode, static state. (**c**) TLC mode, read-only. (**d**) TLC mode, static state. Figure 5: (**a**) Standby current across different operating modes and bias versus dose. (**b**) Standby current versus annealing time. stabilizes. When the annealing time exceeds 10 days, the standby current of the flash memory returns to the initial level. The TID effect introduces a large number of traps in the tunneling oxide layer of the memory, which strengthens the trap-assisted tunneling (TAT) mechanism. When the TID-induced trap state in the oxide was removed by the annealing test, the standby current of the memory decreased. Our findings can provide guidance for the optimal annealing time of CT 3D NAND Flash operating in radiation environments. Considering the time, cost, and memory annealing characteristics, we suggest that the optimal annealing time of the device is 7 days. The cyclic read operation generates a consistent read current, the magnitude of which is recorded. Figure 6 presents the read current in relation to the dose, highlighting an increase in read current proportional to the dose. At a total dose of 40 krad (Si), the read current surges by approximately 1 mA, which means that this memory remains stable and reliable during the TID effect. This memory exhibits robust TID resistance, especially in terms of standby current. When the chip is exposed to a radiation dose of less than 40 krad (Si), the change in standby current across all operational modes is below 15 uA, with an amplitude change under 25%, significantly lower than the figures reported in [12; 17; 18] under comparable conditions. At a dose of 40 krad (Si), the read current escalates from 6 mA to 7 mA, a variation that is less pronounced than that documented in [18]. Alterations in standby current are attributed to the formation of parasitic transistors and the shift in threshold voltage triggered by radiation [22]. C. Threshold voltage  
We obtained the threshold voltage of memory by moving the reference voltage. In this work, Gamma irradiation was performed on the device with all pins grounded, and under SLC mode, the chips were irradiated up to 100 krad (Si). The relationship between the number of bit errors and the increment in bit errors of the memory and the reference voltage are shown in Figure 7; the latter can reflect the threshold voltage distribution of the memory cell. Figure 7a,b demonstrate a decline in the positive threshold voltage for pattern = 00 as the dose escalates. The threshold voltage distribution of the memory cell is Gaussian and the peak value decreases compared to before irradiation.