1/f noise in MOS devices, mobility or number fluctuations?

Recent experimental studies on 1/f noise in MOS transistors are reviewed. Arguments are given for the two schools of thought on the origin of 1/f noise. The consequences of models based on carrier-number ΔN or mobility fluctuations Δμ on the device geometry and on the bias dependence of the 1/f noise are discussed. Circuit-simulation-oriented equations for the 1/f noise are discussed. The effects of scaling down on the 1/f noise is studied in the ohmic region as well as in saturation. In the ohmic region the contribution of the series resistance often can be ignored. However, in saturation the noise of the gate-voltage-dependent series resistance on the drain side plays a role in lightly doped drain LDD mini-MOST´s. Surface and bulk p-channel devices are compared and the differences between n-and p-MOST´s often observed is discussed. The relation between degradation effects by hot carriers or by γ-irradiation on the one hand and the 1/f noise on the other is considered in terms of a ΔN or Δμ. Experimental results suggest that 1/f noise in n-MOST´s is dominated by ΔN while in p-MOST´s the noise is due to Δμ