Compare to mim capacitor , mos capacitor can save much of area, but in circuit design i seldom see people used it , most use mim capacitor ,what is the reason? compare to mim capacitor , what is the disadvantages of the mos capacitor ?
Re: [help] ac-coupliing capacitor can be used mos capacitor
Hi,
Actually what is mim capacitor, can you plz expand /explain it..With the Mos capacitors if we see, though area wise we get the adv..I think in stability ( like leaking and other issues) arer not good with it..
Re: [help] ac-coupliing capacitor can be used mos capacitor
skyeaglemm said:
Compare to mim capacitor , mos capacitor can save much of area, but in circuit design i seldom see people used it , most use mim capacitor ,what is the reason? compare to mim capacitor , what is the disadvantages of the mos capacitor ?
As it's seems to me for prevention of CDM breakdown the mos tr. like ac-coupliing capacitor aren't used. For provide logic "1" of "0" in mos like technology the gates of mos tr. don't connect direct to supply rail, and its connect thought RC (for prevent CDM breakdown). Can anybody explain i'm right?
As I know, voltage coefficient of moscap in strong inversion is low enough for appliations such as opamp compensation cap. But I rarely come across people using the mos cap for opamp compensation even in the cases where strong inversion for mos is gauranteed. Instead people use high area alternatives like mim and poly caps. I think, even the variation of moscap is low across the corners when compared to mim and poly.
Re: [help] ac-coupliing capacitor can be used mos capacitor
the premise for mos capacitor is that it has to operate in strong inversion.
that's to say, the voltage difference between the two nodes of the mos capacitor is rather large, that's the main reason for limiting its application.
in short, the introduce of mos capacitor will influence the dc operating point of the circuit.
I have joined today - and MOSCAP was a random first hit.
Great discussion, regarding the C-V non-linearity of MOSCAP especially near Vth..
my two cents..
1.
MOSCAP - one of the electrode is POLY the other one is the channel (connected to source-drain-shorted-together) - and in MOSCAP usually the length of the channel is much larger than switching MOS (usually MOSCAP channels are squares - same width/length ). The displacement current through the capacitor - reaches metal1 interconnect at the shorted-source-drain contact by drift and diffusion of carriers through the channel - not as good conductance as a metal plate.
Hence this is like:
<Gate-term>---rr--C--rrrrrrrrrrrr---<S_D-term>
by r I meant resistance.
[ Aditional channel implantation makes MOSCAP behave little better ]
MIM structure on the otherhand offers more purer C - less terminal res.
2.
At the lower technology node >90nm MOS gate-oxide is leaky, hence MIM got preference.