Excess high frequency noise and flicker noise in MOSFETs

The noise parameter α=R_ng_m, where R_n is the noise resistance and g_m the transconductance, was measured for n- and p-channel MOSFETs as a function of frequency with the temperature T as a parameter. At lower frequencies α varies as 1/f, as expected for flicker noise, whereas at higher frequencies α attains a limiting value α_∞ that is larger than expected for thermal noise. Arguments are presented whether this high-frequency noise can be hot electron noise. The flicker noise resistance R_mf has a much stronger temperature dependence for n-channel than for p-channel devices; this is related to the energy dependence of the surface state distribution in the forbidden gap.