Current Transport in Polysilicon-channel GAA MOSFETs: A Modeling Perspective

A comparison of modeling approaches for current transport in polysilicon-channel nanowire and macaroni GAA MOSFETs

“…1a as resulting from different polysilicon models described in the previous section, at room temperature (RT) and for different filler oxide radii r f . Similarly to what shown in [31] for nanowire channels, relevant discrepancies appear among the predictions of different polysilicon models in the on-state regime, while negligible mismatches among the models are present in the subthreshold regime. This can be explained by considering that in the subthreshold regime the low free-electron concentration in the intragrain regions and the low trapped-electron concentration at the grain boundaries give rise to weak nonuniformities in channel electrostatics.…”

“…In the presence of variety of approaches, a clear assessment of the impact of different modeling assumptions on the results for the electrical characteristics of the devices has not been provided so far. In this paper, which extends our preliminary work presented in [31], we provide such an assessment, focusing on both the average value and the variability in the electrical characteristics of polysilicon-channel GAA nanowire and macaroni MOSFETs. Figure 1 shows a cross section of the two 3-D polysiliconchannel cylindrical GAA devices investigated in this work.…”

“…In the on-state regime, instead, strong nonuniformities in channel electrostatics arise from the high free-electron concentration in the intra-grain regions and the strong filling of the acceptor traps at the grain boundaries. In particular, the nonuniformities in channel electrostatics result in high energy barriers at the grain boundaries [11,12,31], strongly limiting current transport through the polysilicon channel. This makes the gradual channel approximation less accurate and the activation of thermionic emission at the grain boundaries more relevant for I D .…”

“…3) and of the effective electron mobility (Fig. 4) with respect to the effective medium approximation is the direct consequence of a stronger constraint to the electron flow coming from the relatively high energy barriers arising at the grain boundaries due to acceptor trap filling [11,12,31]. All these differences among the models must be carefully considered when investigating current transport through polysilicon-channel devices in the on-state regime.…”

Random Telegraph Noise in 3D NAND Flash Memories

“…From the viewpoint of current conduction, we can identify two modeling approaches, that differ in the way GBs are treated: one approach is to extend the drift-diffusion model usually adopted in monocrystalline silicon, describing GBs as trapping centers with a reduced mobility [80][81][82]; the other is based on a thermionic emission model at the GBs [83][84][85][86][87]. Although the latter seems to be gaining traction in recent literature, a definitive conclusion has not been reached, yet, and a recent study of the different dependences implied by such models can be found in [88,89]. The above-mentioned numerical models of conduction have been used to investigate the effect of GBs on variability in nanowires [90][91][92][93][94][95] and 3D NAND devices [96,97].…”