Channel length scaling of 1/ f noise in 0.18 μm technology MDD n-MOSFETs

Abstract

Low-frequency (LF) noise (1 Hz–100 KHz) measurements have been performed on 12 n-channel MOSFETs with 5 μm width and 0.23–10 μm varying lengths. The MOSFETs were fabricated using a 0.18 μm, medium-doped-drain (MDD) technology. Interface state density and oxide trap density were extracted from the sub-threshold slope characteristics of I– V GS measurements, and from 1/ f noise measurements, respectively. The McWhorter theory based on long-channel MOSFETs was found to break down for MOSFETs with L<0.6 μm. The drain voltage power spectral density varied inversely with channel length, S V d ∝L −1 for L≥1 μm as expected from the McWhorter theory, but showed a stronger dependence on channel length for smaller devices. Following the Tsai and Ma formulation, a modified McWhorter model has been used, based on threshold voltage variations across the channel. The new model more accurately predicts the Si–SiO 2 interface trap density and the channel length dependence of 1/ f noise magnitude in sub-micron MDD MOSFETs. Three HSPICE 1/ f noise models were evaluated. Although the highest level model provided a good fit to the data for L≥1 μm, for shorter channel devices all three levels underestimate the noise magnitude.