Substrate Effect on the Output Conductance Frequency Response of SOI MOSFETs

Silicon‐on‐insulator MOSFETs models in analog/RF domain

“…Contrarily, simulations performed with self‐heating but without considering the substrate (with the back contact set below BOX) yield only one g d transition in the MHz range related to the self‐heating effect. These confirm that the two transitions in the 10–100 Hz and GHz ranges are indeed caused by the presence of the substrate and have nothing common with either self‐heating or FBEs . Simulations performed with self‐heating and substrate effects turned off result in a flat g d curve without any transitions at frequencies up to 1 GHz.…”

“…Most of studies devoted to the investigation of SOI MOSFETs' specific small‐signal characteristics are focused on the impact of self‐heating and FB effects, while there is lack of attention to the influence of the Si substrate on these characteristics. We have investigated in detail the influence of source‐to‐drain coupling through the substrate on the frequency response of SOI MOSFETs and revealed that this electrical coupling results in two additional transitions in the frequency response , whose characteristic frequencies and amplitudes were found to be very sensitive to the substrate doping as well as to the space‐charge conditions at the substrate–BOX interface. Both measurements and 2D Atlas simulations have been used to prove that the appearance of these transitions is caused by the variation of the potential at substrate–BOX interface (the so‐called floating effective back‐gate effect ) and have no relation to self‐heating and FB effects.…”

“…Furthermore, thin BOX is advantageous for attenuation of self‐heating effects. However, with BOX thinning and channel length scaling, the role of source‐to‐drain fringing coupling through the substrate (or variation of the potential at the substrate/BOX interface) becomes more important, which results in stronger G DS degradation with frequency . Indeed, the degradation of G DS with frequency, caused by the variation of C sub , drastically increases with BOX thickness decrease .…”