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

Abstract

The two main sources of low-frequency flicker noise are mobility fluctuations and number fluctuations. Our experiments on NMOS noise measurements were done from subthreshold to saturation region of operation for both long-channel (5 /spl mu/m) and short-channel (as small as 0.6 /spl mu/m) NMOS transistors. The results suggest that for both types that in the saturation region, the flicker 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-channel devices, due to the effects of velocity saturation and the resulting nonlinear transconductance (g/sub m/) variation with gate bias voltage, the input-referred voltage noise increases as the gate-source voltage increases instead of staying constant as it does for long-channel devices. In the subthreshold region, the input-referred voltage noise decreases drastically as the gate-source voltage increases for both long-channel and short-channel NMOS devices. Simulations have been done using PSPICE and HSPICE, with noise level (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 favorably with the measured noise phenomena for the short-channel and long-channel NMOS devices, respectively.