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Design >> Mixed-Signal Design >> MIM CAP shielding problem
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Message started by abcyin_DG on Jul 16^th, 2013, 11:29pm

Title: MIM CAP shielding problem
Post by abcyin_DG on Jul 16^th, 2013, 11:29pm

Hi, all,

In some processes, I see some mim-caps are shielded with lower metal layer beneath the capacitor plates, and the design manual will suggest to connect the shielding to ground.
I am wondering that whether the shielding is necessary for RFIC purpose? and what's the difference between connecting to GND and VDD? which one is better?

Best wishes,
abcyin

Title: Re: MIM CAP shielding problem
Post by raja.cedt on Jul 18^th, 2013, 12:39am

Hello,
As far as shielding concern, there is no difference between vdd and vss. But keep in mind that shielding will increase capacitive load and keeping ac gnd under the capacitor will only shield against substrate noise. Even there are other techniques like keeping an nwell, or keeping poly shield which will add less capacitance compared to metal layers.

Have fun,
Raj.