Analysis of threshold voltage variability due to random dopant fluctuations in junctionless FETs

An analytical formulation of the threshold voltage variance induced by random dopant fluctuations in junctionless transistors is derived for both cylindrical nanowire and planar double-gate structures under uniform channel and constant mobility approximation. Results from drift-diffusion-based numerical methods are in reasonable agreement also for large Vds, including mobility variations, and for short gate lengths. The results clearly indicate that the threshold voltage fluctuations can become a concern with the reduction of the critical dimensions.