Substrate Effect on the output conductance frequency response of SOI MOSFETs

The paper analyzes the influence of the Si substrate on the AC characteristics of silicon-on-insulator (SOI) MOSFETs through 2D Atlas simulations and measurements. It is shown that the presence of the Si substrate underneath the buried oxide (BOX) results in two transitions in the frequency response of the output conductance, caused by the variation of the potential at substrate-BOX interface. A first-order small-signal model is proposed to support the obtained results. It is demonstrated that the appearance of “substrate-related” transitions, their position and amplitude depend strongly on the substrate doping, space-charge conditions at substrate-BOX interface, temperature and moreover become more pronounced with device downscaling.