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Spectre / BSIM 4.7 MOS Parameter
Sep 08^th, 2016, 10:11am

Hello,

I performed a DC OP simulation and I back-annotated the basic OP parameters and all terminal currents of a PMOS device in my circuit:

I was quite surprised to see that only half the drain current/leakage comes from the bulk (3.428pA). The current through the channel is tiny (3.871fA) yet there is a source current that amounts to the remaining half of the leakage.

To identify where the source current comes from, I printed all the DC OP parameters for P8:

To my surprise, there is no bulk current flowing through P8, and the total drain current of 6.854pA in the screenshot above appears to be modeled by the "ide" parameter.

1) What are "ide", "ibe" and "idb" parameters?

2) I am assuming that "id" is the total drain current which should match the annotated drain current above; if not, and this is actually parameter "ide", then what is "id"?

3) Most importantly and more to the point, where is the total drain current coming from? How can I find out?

Thanks very much in advance for your help �:)

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Geoffrey_Coram

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Re: Spectre / BSIM 4.7 MOS Parameter
Reply #1 - Sep 9^th, 2016, 8:07am

What simulator are you using? If you're using Spectre, you could do "spectre -help bsim4" and see what it reports for those operating-point parameters.

However, I noticed that ide = -6.854p matches exactly with the back-annotation you showed for the drain terminal current, and ibe = 3.428p that for the body terminal current. idb is usually used for the drain-body junction current.

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Geoffrey_Coram Senior Fellow Offline Posts: 1999 Massachusetts, USA	Re: Spectre / BSIM 4.7 MOS Parameter Reply #2 - Sep 9^th, 2016, 8:08am What about GIDL/GISL currents or Isub?
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Blacksmith

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Re: Spectre / BSIM 4.7 MOS Parameter
Reply #3 - Sep 9^th, 2016, 12:16pm

Geoffrey_Coram wrote on Sep 9^th, 2016, 8:07am:

..Spectre, you could do "spectre -help bsim4" and see what it reports for those operating-point parameters..

I wasn't aware I could extract the parameters so easily �:)

It turns out that "id" is the "resistive drain current" whatever this means. It certainly isn't the current through the channel, since that's "ids". As previously suspected, "ide" is the total drain current.

Either way, this doesn't answer the relatively speaking excessive drain current and where it's coming from. An explanation for this current, as a colleague highlighted, is the default value of gmin. In this case, 1/gmin is 1pΩ and the drain voltage is at ~3.8V; this amounts to ~3.8pA flowing through the drain 1/gmin resistor.

Thanks for the help!

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