Our paper presents a quantum mechanical treatment of low-frequency noise in scaled NMOS transistors to extend the "unified" noise model and includes remote Coulomb scattering and surface roughness - the latter is a new consideration in the theory. Our experimental work focuses on scaled NMOS devices with a composite dielectric consisting of a 0.5 nm SiO2 covered with a high-K, 1.6 nm HfO2 with a metal gate. In the past, Coulomb scattering was assumed to arise from trapping centers located at the Si-SiO2 interface; however, this cannot give rise to a 1/f noise spectrum. We model remote Coulomb scattering into the dielectric film as traps in these films easily lie within a tunneling distance from the interface. This approach explains the decrease in the Coulomb scattering parameter (alpha) as a function of gate voltage. In addition, we introduce surface roughness scattering through fluctuations in the normal electric field due to fluctuations in the free carrier density with a surface scattering parameter (beta) proportional to the SPICE surface roughness parameter, 0(s). Good agreement is obtained between our model and experimental results for both I-DS-V-GS and the power spectral density, S-td, characteristics in very strong inversion region where surface quantization of the 2D subbands is strong. (C) 2012 Elsevier Ltd. All rights reserved.