Analysis of the radiation effects in a device is of great importance. The gate all around (GAA) structure that contributes to device scaling not only solves the short channel effects (SCE) problem but also makes the device more resistant in radiation environments. In this article, the total ionizing dose (TID) simulation of nanowire FET (NW) and FinFET was performed. Both these devices were compared and analyzed in terms of the shift of threshold voltage (V T ). The channel insulator was composed of two materials, SiO 2 and HfO 2 . To improve the accuracy of the simulation, the interfacial trap parameter of SiO 2 and HfO 2 was applied. Based on the simulation result, the NW with a larger oxide area and larger gate controllability showed less V T shift than that of the FinFET. It was therefore proved that NW had better TID resistance characteristics in a radiation environment. The gate controllability was found to affect the TID effect more than the oxide area. In addition, we analyzed the manner in which the TID effect changed depending on the V DD and channel doping.
The main cell channel in 3D NAND flash structures easily goes into the floating state, because it is not directly connected to the substrate, resulting in the down-coupling phenomenon (DCP). As DCP reduces the boosting potential of the inhibit string during the program and verify operations, the natural local self-boosting (NLSB) effect is reduced, which in turn reduces the channel potential and causes a program disturb. However, if the channel potential of the selected word line (WL) is significantly increased by excessive NLSB, a hot carrier injection (HCI) occurs due to the potential difference between the adjacent WLs, even at a low channel potential. Therefore, we introduced a dummy WL to reduce HCI.
In this paper, we proposed a novel structure enabling the low voltage operation of three-dimensional (3D) NAND flash memory. The proposed structure has a ferroelectric thin film just beneath the control gate, where the inserted ferroelectric material is assumed to have two stable polarization states. A voltage for ferroelectric polarization (VPF) that is lower than the program or erase voltage is used to toggle the polarization state of the ferroelectric thin film, whose impact on the channel potential profile is analyzed to optimize operation voltage reduction. The channel potential of select word line (WL), where the natural local self-boosting (NLSB) effect occurs, increases due to the polarization state. Model parameters for the ferroelectric thin film of 8 nm are fixed to 15 µC/cm2 for remanent polarization (Pr), 30 µC/cm2 for saturation polarization (Ps), and 2 MV/cm for coercive field (Ec). Within our simulation conditions, a program voltage (VPGM) reduction from 18 V to 14 V is obtained.
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