Hi,
I'm currently working on compact modeling of multiple-gate MOSFET. I used charge-based model approach to model my device and now try to validate my compact model with TCAD simulation results. How can I extract the inversion charge density (as shown in the uploaded figure) that is bias dependent (source/drain) from Silvaco TCAD?
Dear Afiq,
What is vertical axis represent and its units.
From the conceptual point of view you have to simulate your device to get the performance parameters as you defined in the model. For example you have to calculate by your device simulator here TCAD , the inversion charge Qin as a function of the the applied gate voltage For VDS=0 and VS=0. In this case you can curve fit your analytical equation with that calculated from the simulator and get the model parameters.
For the first order MOSFET model:
Qin= Cox( VGS- Vthn)
So, the model parameters here are Cox and Vthn which can be determined by the curve fitting.
The final comment, it is better here for the above equation to use linear plot not a semilog plot.
Best wishs
It may not be accurate to extract the inversion charge from I-V curves.
Conceptually, inversion charge can be extracted by fitting I-V curves, as Dr. Zekry mentioned above. (extract Vth according to your analytic model, calculate Cox analytically, and then extract the inversion charge)
It is better to extract the inversion charge using C-V curves, whether your Silvaco TCAD has the module to do the C-V or not.
Best regards,
Jun-Sik Yoon
Dear Jun,
Welcome,
I am aware of that and proposed also to calculate Qin using the equation given in my first post. So, one would need to have Cox and Vthn known.
Best wishes
Thank you all for the helpful comments. I have obtained the Qin using the first order model as suggested by Prof. Halim (شكرا):
Qin+Qdep=Cox*(Vg-wf-Vpsi); depletion charge, Qdep; workfunction difference, wf; and surface potential, Vpsi.
But I'm also curious if its even possible to extract the value directly from the simulation?
And secondly, how can we extract the value from C-V? (Silvaco can plot the CV graph)
Kind regards,
Afiq Hamzah
Dear Afiq Hamzah,
If you perform small signal AC analysis in Silvaco, you will be able to obtain different capacitance values when you excite each terminal using a miniscule sinusoidal AC signal. (please refer to AC analysis in Silvaco manual).
By integrating these capacitance values according to the quasi static current equation provided in Prof. Yannis's book "Operation and Modelling of MOS transistor", Chapter 9, you can obtain the terminal charges Qg, Qb, Qs, and Qd. Qinv = Qs+Qd.
Please note that the equations are in time domain, but by using C=dQ/dV, you can manipulate the equation to be independent of time and rather dependent on frequency. Since you will use a very low frequency for quasi static approximation to apply (and you can fix your ac analysis to one static frequency), your equation can further reduce to frequency independent equation.
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