Low-frequency noise and mobility in triple-gate silicon-on-insulator transistors: Evidence for volume inversion effects

The low-frequency noise (LFN) characteristics of triple-gate MOSFET with various fin widths are shown to exhibit 1/f type dependence. We show that LFN is generated by two parallel mechanisms, involving (i) the carrier number fluctuations due to trapping/release phenomena on the near-interface traps and (ii) the carrier mobility fluctuations in the channel. The relative contribution of each mechanism to LFN depends on the biasing conditions and varies with the fin width. The region of dominance of model (i) can be used for extracting the effective trap density, Nt, which decreases as the fin becomes thinner. That is attributed to the carrier confinement in the central part of the transistor body, due to the volume inversion. The volume inversion effect is confirmed by independent measurements of low-field mobility, shown to be enhanced with the reduction of the fin width. The model (ii) contributes to LFN, only at small current values as it exhibits a power spectral density dependence varying as 1/Id. Random telegraph noise is manifested in small volume devices.