A quantum mechanical treatment of low frequency noise in high-K NMOS transistors with ultra-thin gate dielectrics

Abstract

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 0.5nm SiO2 covered with a high-K, 1.6nm 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 (α) 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 (β) proportional to the SPICE surface roughness parameter, θS. Good agreement is obtained between our model and experimental results for both IDS–VGS and the power spectral density, SId, characteristics in very strong inversion region where surface quantization of the 2D subbands is strong.