Impact of the high vertical electric field on low-frequency noise in thin-gate oxide MOSFETs

In this paper, quantum effects induced by the high vertical electric field, i.e., inversion layer quantization and gate current tunneling, are taken into account to model the low-frequency noise behavior of 0.13 μm technology node thin gate oxide MOSFETs. First, we show that the modifications induced by inversion layer quantization in the band structure and spatial distribution of the inversion layer carriers must be taken into account when extracting an effective density of traps from 1/f noise measurements. The ultrathin gate oxide and the high substrate doping of scaled MOSFETs create a strong electrical field in the inversion layer, which causes the surface conduction (n-) or valence (p-MOSFET) band to split into discrete energy levels. The first allowed state resides then above (below) the conduction (valence) band level in the bulk, giving rise to a band gap widening and in addition the spatially localized charge centroid is at a finite distance from the SiO₂/Si interface. The impact on both dc and noise parameters of these quantum effects have been numerically calculated and compared to experimental results. The main conclusions coming out of this study is that if the inversion layer quantization is neglected, inaccurate oxide trap densities will be derived from the input-referred voltage noise spectral density S_VC:. A similar conclusion will hold for the extraction of the scattering coefficient derived in the frame of a correlated number fluctuations model or for the effective Hooge parameter, derived from the normalized drain current spectral density S_ID/I_D². Finally, a particular gate tunneling mechanism namely Electron Valence Band (EVB) tunneling is shown to modify the noise behavior of thin gate oxide devices in terms of a self-biasing body effect.