Complex random telegraph signals in 0.06 μm2 MDD n-MOSFETs

Medium doped drain n-MOSFET with W-eff x L-eff = 0.29 x 0.20 mu m(2) have been used to investigate complex random telegraph signals (RTS) in the drain to source voltage. Four-level switching events were observed, from which three discrete traps were distinguished. Their behavior was observed in the range of gate-to-source and drain-to-source voltages of 0.5-1.8 V, all in strong inversion. The capture and emission times of each trap were investigated as a function of gate bias as well as drain voltage. Using the mark-space ratio of the switching events, the position of the traps from the Si-SiO2 interface was calculated to be about 0.43, 0.55 and 0.74 nm. These evaluations were used successfully to determine the trap energy level with respect to oxide conduction band edge. Comparative evaluation of the mobility fluctuations with respect to number fluctuations was done using RTS amplitude. The screened scattering coefficient due to the Coulomb scattering effect was examined with respect to the variation of carrier density in the channel as well as in the drain voltage for all three traps. An influence of one trap on another was observed and found that there is a change of the energy level of 0.06 eV due to this effect. (C) 2000 Elsevier Science Ltd. All rights reserved.