The impact of random dopant fluctuation (RDF) on the performance variation of a PNPN feedback field effect transistor (PNPN FBFET) is investigated using a 3D technology computer aided design tool. To investigate RDF-induced device performance variation (e.g. threshold voltage (V TH ) variation), the nominal doping profile of each region in a PNPN FBFET is separately randomized. Consequently, in terms of RDF-induced V TH variation, the channel-2 region (i.e. gated channel region) plays a key role as a main contributor to V TH variation, as it is the most decisive region for determining gate-to-channel controllability. As an example, the value of σV TH resulting from the channel-2 region is nine times higher than that from the channel-1 region. Based on the simulation results, guidelines for variation-immune device design are comprehensively discussed.
A tunnel field-effect transistor with segmented channels (Seg-TFET) on a corrugated substrate is proposed. The Seg-TFET takes advantage of using three stripes and the selective contact configuration to define the direction of current, and thereby its device performance can be improved. Furthermore, the process flow of the Seg-TFET demonstrates a substantiation of the new device structure. Consequently, its current flow is simply defined by adjusting the appropriate contact configuration at metal-zero-level without any additional front-end-of-line process.
For stacked multiple-channel-structure devices such as stacked nanowire FETs (stacked NWFETs), work-function variation induced (WFV-induced) threshold voltage (V T ) variation is quantitatively investigated using a three-dimensional technology computer aided design (TCAD) tool. In the stacked structure device, the more nanowires are stacked, the more the WFV-induced V T variation can be decreased. It is proposed that the ratio of average grain size to gate area (RGG) for stacked multiple channel structures can be used to estimate the WFV-induced V T variation. For accurate estimation, the effective gate area (GA eff ) should be considered in the stacked structure, as the variation is averaged out by stacking multiple channels. If two 3-stacked NWFETs have the same GA eff but different nanowire diameters (i.e. one with 10/10/10 nm and the other with 7/9.34/13 nm), the two would have identical WFV-induced V T variation. In this context, if a single NWFET and a 2-stacked NWFET have identical GA eff , the two would have the same V T variation. Using the RGG concept with GA eff enables the WFV-induced V T variation to be precisely estimated, regardless of nanowire diameter and the number of nanowires.
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