Excess Lorentzian noise in partially depleted SOI nMOSFETs induced by an accumulation back-gate bias

It is shown that the application of an accumulation back-gate bias (V_GB) to partially depleted silicon-on-insulator nMOSFETs induces an excess Lorentzian noise component in the front-channel current noise spectral density. The effect is observed for front-gate biases (V_GF) from weak to strong inversion. Below the threshold for electron valence band (EVB) tunnelling, the parameters of the Lorentzian noise are independent on V_GF, but strong functions of V_GB. Given the similarity with the behaviour of the EVB tunnelling-related noise overshoot, the observations are interpreted in a similar way. It is proposed that the additional source of floating-body related excess Lorentzian noise is shot and thermal noise in the body charge, filtered by the RC impedance of the source-body junction. The possible origin of the body-charge fluctuations and related shot and thermal noise will be discussed.