A 1/f noise technique to extract the oxide trap density near the conduction band edge of silicon

The use of 1/f noise measurements in n-channel MOSFETs to extract the oxide trap density in space and energy near and above the conduction band edge of silicon is investigated. The conventional carrier number fluctuation model of 1/f noise that attributes 1/f noise to the trapping and detrapping of inversion layer carriers by oxide traps is reviewed. It is shown that oxide band bending in devices with a nonuniform oxide trap distribution leads to a gate voltage dependence in the magnitude and exponent γ(V_gs) of the 1/f^γ noise spectrum. An extension of the 1/f noise number fluctuation model that includes both carrier number fluctuations and correlated mobility fluctuations is then studied. Correlated mobility fluctuations are attributed to the coulombic scattering of inversion layer carriers by the fluctuating trapped charge. It is shown that the correlated fluctuation model predicts a gate voltage dependence in the magnitude and exponent γ of the 1/f^γ noise spectrum even for a uniform oxide trap distribution. By analyzing the 1/f noise magnitude and exponent data in n-channel MOSFETs having various oxide thicknesses, both models are used to extract the oxide trap density over a wide range of space and energy