## 4 Investigation of \(Z\)-Interference  
Figure 9a shows the Z-interference characteristics, indicating the amount of change in the victim cell Vth according to the change in the attack cell Vth for each structure. The results show that the Z-interference characteristics deteriorate exponentially when the attack cell Vth is programmed to 2 V or more during Ls and Lg scaling compared to the reference. Additionally, the amount of \(Z\)-interference degradation is greater during Lg scaling compared to Ls scaling.  
To determine the cause of these changes, we examined the change in electron density within the poly-Si channel before and after programming the attack cell for each structure, as shown in Figure 9b-g. The results indicate that the decrease in electron density in the lower part of the WL before and after the attack cell programming is much larger during Lg scaling compared to Ls scaling.  
Figure 10a-c quantitatively compare the electron density before and after the attack cell program by cutting the poly-Si channel area in Figure 9b-g. The results reveal that the electron density in the victim cell and spacer area decreases by more than 10 times during Lg scaling compared to Ls scaling. To analyze this cause, we checked the Id-Vg curve of the victim cell after the attack cell program for each device, as shown in Figure 10d. The results indicate that the change in sub-threshold swing (SS) characteristics of each device varies significantly depending on the attack cell program. Notably, the amount of SS deterioration  
Figure 8: Program and erase window of selected WL under various Lg and Ls scaling conditions.  
is much larger during Lg scaling compared to Ls scaling, which is interpreted as a more severe deterioration of gate controllability during Lg scaling.  
Figure 10: Comparison of electron density before and after the attack cell program by cutting poly-Si channel area in Figure 9b–g in case of (**a**) reference, (**b**) Ls scaling, and (**c**) Lg scaling. (**d**) Id-Vg curve of victim cell after attack cell program for each device.  
Figure 9: (**a**) Comparison of Z-interference in reference, Lg scaling, and Ls scaling structures. Change in electron density within poly-Si channel before and after programming attack cell in (**b**,**c**) reference, (**d**,**e**) Lg scaling, and (**f**,**g**) Ls scaling structures.  
In general, the Z-interference characteristic tends to improve as the gate-to-substrate controllability of the selected WL increases [11]. Therefore, a large SS on the Id-Vg of the selected WL implies weak gate controllability, which suggests greater vulnerability to Z-interference characteristics. Thus, it can be inferred that the deterioration of gate controllability during Lg scaling compared to Ls scaling further accelerates the deterioration of Z-interference.  
Additionally, this phenomenon of gate controllability deterioration can be indirectly confirmed by comparing the tendency of initial Vth reduction in Figure 2a. The Vth roll-off phenomenon due to SCE is more noticeable during Lg scaling compared to Ls scaling. This decrease in the Vth indicates a weakening of gate controllability [15]. Moreover, a large initial Vth reduction means that a larger amount of electrons must be stored when programming an attack cell to achieve the same programmed Vth value. This change is thought to be the cause of additional Z-interference degradation during Lg scaling.