Performance estimation and Variability from Random Dopant Fluctuations in Multi-Gate Field Effect Transistors : a Simulation Study

Abstract: As the formation of nearly abrupt p-n junctions in aggressively scaled transistors has become a complex task, a novel type of device in which there are no junctions has recently been suggested (J. P. Colinge et al., Nature 2010). The device of interest is referred to as the junctionless transistor, and it has demonstrated excellent functionality, with the advantage of a simpler fabrication process than conventional FETs. Despite the remarkable performances exhibited by the junctionless transistor, this device has to be tested against variability before it may be produced in large scale. Hence, the study of how the fluctuations in the number and in the position of the dopant atoms affects a large number of devices has been developed in this work. Such variability source is referred to as Random Dopant Fluctuations (RDF) and it is among the most critical ones for conventional MOSFETs. Our view is that RDF ought to largely affect the junctionless transistors. Hence, in this work we mainly aim at investigating the impact of RDF in these type of devices. Firstly, we provide a detailed analysis on the performance of an ideal junctionless transistor with a uniform non-random doping concentration, by mean of simulations developed using a TCAD software. Secondly, we investigate the effects of RDF in the junctionless transistor, as the principal aim of our study. Here, we determine how the I-V characteristics are affected by the random dopants and we illustrate fundamental the causes of the variations. A first estimation of the impact of RDF is provided by the illustration of the threshold voltage and beta [1] distributions, and by the computation of the fundamental statistical quantities relating to the two parameters. A further and last estimation is provided by the comparison obtained studying RDF on the inversion mode FET.