SPICE models for flicker noise in n-MOSFETs from subthreshold to strong inversion

The two main sources of low-frequency flicker noise are mobility fluctuatio ns and number fluctuations. Our experiments on NMOS noise measurements were done from subthreshold to saturation region of operation for both long-cha nnel (5 mum) and short-channel (as small as 0.6 mum) NMOS transistors. The results suggest that for both types that in the saturation region, the flic ker noise is due to the surface state effect and the noise equations, NLEV = 2 and 3, in SPICE, HSPICE, and PSPICE are most appropriate. For short-cha nnel devices, due to the effects of velocity saturation and the resulting n onlinear transconductance (g(m)) variation with gate bias voltage, the inpu t-referred voltage noise increases as the gate-source voltage increases ins tead of staying constant as it does for long-channel devices. In the subthr eshold region, the input-referred voltage noise decreases drastically as th e gate-source voltage increases for both long-channel and short-channel NMO S devices. Simulations have been done using PSPICE and HSPICE, with noise l evel (NLEV) = 3 and device model level 3 and BSIM 3.2 and 3.3. The results from PSPICE version 8.0 level 7 (BSIM 3.3) and SPICE level 3 compare favora bly with the measured noise phenomena for the short-channel and long-channe l NMOS devices, respectively.