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# how can i get c-v curve for mos cap and mim cap

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#### fencl

##### Member level 1
Hi all ,there's some problem cunfused me
how can i get c-v curve for mos cap and mim cap just used hspice?
Besides how can i get very small capacitance such as 2fF by norminal 0.13um/0.18um process?
since i need these small cap array.can anyone tell me way for coarse value or fine value?

Thanks

1-fF is a really small cap in those processes. Your logic cap and more importantly wire caps are in the same order. So, make sure you don't lose tunability

mhaghaed said:
1-fF is a really small cap in those processes. Your logic cap and more importantly wire caps are in the same order. So, make sure you don't lose tunability

yes, from 0.18um process files ,mim cap can hold nearly 7~8fF at least. by simply use two cap in series,we can get about 3~4fF, but is it the only way, since the gate voltage will always change in quite range.

BTW,since ac analysis can calculate cap value, c=1/2*pi*imagz(in)*f,i'm poor in s and p parameter of hspice, who can help to explain it clearly?

the MOS cap value depends on the thickness of oxide ,
the Cox formula = episilon/ Tox , if the side wall cap can be ignored ,
for roughly estimation , 100A thickness process the Cox is about 2fF /um2.

Note : 100A = 100 Angstrom

you can use .option captab at hspice input deck to get it !

pianomania said:
the MOS cap value depends on the thickness of oxide ,
the Cox formula = episilon/ Tox , if the side wall cap can be ignored ,
for roughly estimation , 100A thickness process the Cox is about 2fF /um2.

Note : 100A = 100 Angstrom

you can use .option captab at hspice input deck to get it !

thanks for reply. i have find some way such as captab,directly probe cap.and ac analysis for it's value.
actually,mos cap can hold up to 1fF or more ,but it has a drawback that depend on gate voltage. since my cao array is used for tuning(means the voltage is uncertain all the time) ,i'm affraid it can't work well

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