# Temperature Impacts on Endurance and Read Disturbs in Charge-Trap 3D NAND Flash Memories
## 5 Read Disturb  
It is known that high temperature can accelerate the speed of lateral charge migration in the storage layer and modulate the threshold voltage distributions of memory cells [8].  
Figure 4: Cross-temperature characterizations to study degradation at various temperatures. The first and third stages were fixed to 25 \({}^{\circ}\)C, while the second stage selected three different temperatures, \(-\)30, 25, and 70 \({}^{\circ}\)C. The RBER was normalized by the first point of the RBER to compare the degradation trends of each condition.  
Figure 3: (a) Measured RBER with P/E cycling at different temperatures; (b) normalized RBER to study RBER degradation.  
These factors can cause read disturb properties to become more complex at various temperatures. To understand the temperature impacts, we designed the following experiment: firstly, setting the work temperature of the chamber to the target temperature ranging from \(-30\) to \(70\)\({}^{\circ}\)C; then, programming randomized data with subsequent 3000 times read cycling. For detail analysis, data were dumped and recorded every 100 times.  
Measured read disturbs are summarized in Figure 5. Firstly, it was observed that RBER degradation turned out to be much more serious at cold temperatures; secondly, for high-temperature operations at \(70\)\({}^{\circ}\)C, a part of RBER can be recovered after serval times reading. Considering that the total RBER included two parts, down-shift errors from the charge loss and up-shift errors from charge accrual, we divided the total error bits to two groups for in-depth analysis: down-shift errors and up-shift errors. As shown in Figure 6, for read disturb-related RBER degradations, down-shift errors were the dominant part with clear temperature dependences, indicating that RBER changes mainly originated from the charge loss. Down-shift error degradation was much stronger at sub \(-25\)\({}^{\circ}\)C, but it could be well suppressed at high temperatures, which can be explained by the narrower V\({}_{th}\) distributions at high temperatures [16]. The interesting phenomenon was that read disturbs from up-shift errors showed the opposite tendency while increasing the operating temperature. For read cycling at \(70\)\({}^{\circ}\)C, up-shift error bits can be partly recovered with read cycles. It was noticed that the decreasing error bits were mainly from cells with high program levels, like F-to-G errors in F-level cells. It should be noted that, as shown in Figure 6f, lower F-to-G error bits can be observed in the whole temperature range from \(-30\) to \(70\)\({}^{\circ}\)C. However, G-to-F up-shift error bits are largely suppressed at \(70\)\({}^{\circ}\)C. Thus, with combined down-shift and up-shift errors, we observed abnormal \"recovery\" at \(70\)\({}^{\circ}\)C while performing read cycling.  
For further understandings, the word-line (WL) dependences of fail bit counts (FBCs) change at \(70\)\({}^{\circ}\)C were studied in detail. By comparing the data from the 1 st and 3000 th read cycles, it was observed that the dependence of the major state error decreased on the WL index. As shown in Figure 7, error bits from D-E, E-F, and F-G errors showed obvious decreasing trends in higher WL index, and each read cycle in this experiment followed the same observation. In other words, the WLs of the middle-to-low index were the dominant origins for the lower up-shift errors that were attributed to the observed error bits \"recovery\" at \(70\)\({}^{\circ}\)C.  
Figure 5: Read disturb characterizations at different temperatures from \(-30\) to \(70\)\({}^{\circ}\)C.