# Total Ionizing Dose Effects in Advanced 28 nm Charge Trapping 3D NAND Flash Memory
## 3 Results and Discussions
Conversely, Figure 7c,d reveal that the negative threshold voltage for pattern = FF remains largely unaffected by TID. Figure 8 showcases the failure thresholds of Flash memory across various operating modes (TLC/SLC) and bias states under TID effects. The bias states include read-only, static state, and dynamic erase-program-read cycles. Functional failure is identified when multiple pages are operated upon, and at least one page's read-back data are entirely  
Figure 6: Read current versus dose (SLC mode—read-only state). incorrect, rendering the data irrecoverable. The dynamic erase-program-read state exhibits the lowest failure threshold, highlighting its vulnerability to TID effects. The experimental results reveal that for pattern = 00, the corresponding positive threshold voltage diminishes with increasing TID, aligning with prior research [23; 24]. However, for pattern = FF, the results diverge. This study observes minimal impact from radiation, contradicting the existing literature where pattern = FF is also susceptible to TID [22]. The variation in threshold voltage is attributable to the change in charge in the charge trapping layer of the memory cell, with TID leading to charge loss [22; 24; 25]. D. Type of Bit Flip  
Figure 8: The failure thresholds of Flash memory under varied operating conditions. Figure 7: The relationship between the threshold voltage and radiation dose. (**a**) Pattern = 00, byte errors vs. reference voltage. (**b**) Pattern = 00, the increment in byte errors vs. reference voltage. (**c**) Pattern = FF, byte errors vs. reference voltage. (**d**) Pattern = FF, the increment in byte errors vs. reference voltage. Figure 9 shows the number of bit flips of CT 3D NAND Flash operating in TLC mode at different doses. In the case of radiation resulting in the loss of the same amount of charge, SLC mode will only appear with 0 becomes 1 bit flip, while for TLC mode, due to the characteristics of its programming state, both 0 becomes 1 and 1 becomes 0 can occur, i.e., there will be one or more flips when reading. For pattern = AA, as the dose increases, the frequency of flips also rises, predominantly manifesting as 1-bit flips without exceeding a 5-bit threshold, attributed to the exclusive occurrence of 0 becomes 1 flips. Conversely, in the context of pattern = 00, 1-bit flips are more prevalent at doses below 30 krad (Si), but higher doses lead to a predominance of multi-bit flipping. When the number of multi-bit flip bits exceeds 4 bits, this means that two adjacent cells are faulty. The exclusive observation of 0 becomes 1 flips in this study contrasts with the findings reported in [26]. The incidence of bit errors in TLC mode exceeded that in SLC mode, aligning with the conclusions of [25]. Bit flipping is primarily caused by the loss of electrons from the memory cell's charge trapping layer, a process exacerbated by radiation. This radiation damage leads to electron depletion and the emergence of uncompensated positive charges in the oxide layer, which facilitate the flipping of bits together. E. Erase Block and Program Page Timing  
Figure 10a,b demonstrate that the time required to erase a block decreases with the increasing dose in both SLC and TLC modes. Figure 10c shows an increase in program page time in TLC mode for doses exceeding 20 krad (Si). Figure 10d indicates that Flash operation in SLC mode remains unaffected by total dose effects below 30 krad (Si). However, when this threshold is exceeded, the program time operating in a static state will be reduced. Figure 10a-c highlight that the memory operating in a cyclic read state is the most vulnerable to radiation exposure. Figure 9: The number of bit flips versus dose in TLC mode. (**a**) Pattern = AA, read-only. (**b**) Pattern = AA, static state. (**c**) Pattern = 00, read-only. (**d**) Pattern = 00, static state. Previous research [19] examined the TID effect on erase time, finding a decrease in erase time with increasing dose, aligning with our observations. Ref.