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Unexpected behavior/values seen in small-signal models of thin-oxide devices. #34
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Dear Boris, find attached our results documentation for the compact models of the MOSLV. We converted the existing spice models to ngspice format. Regarding fT: As you can see, the fT does not show such a kink for the analyzed devices. fT = f/Im(Y11/Y21) (where f is a spot frequency) You must run an AC analyis. Regarding Overlap caps: Let us do an approximate calculation based on the model parameters of the LV NMOS and the model equations.
The model parameter CFRW (outer fringe capacitance for 1 um wide device)
evalutes to 0.2 fF/um for rfmode=1. It sets Qfgs. The model variable that sets Qgs_ov is
, which depends on several model parameters that are physics-based.
CGOV_p = 8.85e-12 F/m * 3.9 * 5um * 30nm/2.2nm = 2.4 fF The total CGSOV for a 0.13/5 device is 3.4 fF. This corresponds to around 0.68 fF/um. Thus, the model in ngspice works as it should. The question is if the parameters LOV and CFRW are |
Hello Boris, I'm forwarding this issue to our IHP modeling experts.. |
The physical origin of the large cgsol is largely the LOV parameter (see my calculation) that can be taken from cross-sections. One could check that. |
Thank you, everyone. BTW, I looked at the docs here: https://github.com/IHP-GmbH/IHP-Open-PDK/tree/main/ihp-sg13g2/libs.doc/meas/MOS/doc. I am getting very large values for Cov when I divide the measured cap by the give width. But, I am not sure if I am interpreting the data correctly. |
See here for an observation regarding the model usage of number of fingers: #164 |
For reference, here is my Jupyter notebook that produces these data:
https://github.com/bmurmann/Ngspice-on-Colab/blob/main/notebooks/IHP_SG13G2_VGS_sweep.ipynb
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