Author Topic: Apparently silicon capacitors are a thing...  (Read 1291 times)

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Offline daqq

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Apparently silicon capacitors are a thing...
« on: October 31, 2018, 09:39:11 pm »
This seems pretty interesting:

https://www.mouser.sk/Passive-Components/Capacitors/Silicon-Capacitors/_/N-5g95?Ns=Capacitance|1

According to the datasheet, they are very stable, pretty much ignoring temperature and DC bias, while being small enough (in particular, they are thin), pretty much no ESL and have a fairly high capacity for the given size. Not the highest, but still cool. They are pricey.

I wonder, with the best processes available (stuff like intels 10nm and so), what's the biggest amount of capacitance (assuming a very high budget) you could fit into, say, a 0603?
« Last Edit: October 31, 2018, 09:46:54 pm by daqq »
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Offline tooki

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Re: Apparently silicon capacitors are a thing...
« Reply #1 on: November 01, 2018, 03:06:45 am »
Well, it's not surprising, insofar as ICs often contain tiny capacitors etched right into the silicon. I assume similar (if not identical?) processes are used for these.
 

Offline Zero999

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Re: Apparently silicon capacitors are a thing...
« Reply #2 on: November 01, 2018, 09:37:58 am »
 

Offline amyk

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Re: Apparently silicon capacitors are a thing...
« Reply #3 on: November 01, 2018, 12:07:39 pm »
Those have an operating temperature up to 200C.

The lower maximum temperatured ones are not quite as expensive, but still several orders of magnitude more than ceramics...
 

Offline GeoffreyF

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Re: Apparently silicon capacitors are a thing...
« Reply #4 on: November 01, 2018, 02:01:42 pm »
Actually every silicon junction device is, to some degree, a capacitor.  I've done circuits where an LED is charged up with pulses just below what produces light.  Then the discharge of capacitance is measured to detect light striking the LED.  It's a very narrow band detecting light slightly longer wave length than the LED produces.   Good hack for detecting a variety of wavelengths.

Junction capacitance is generally a factor in some other designs.

Anything that is dielectric (and that's a lot of things) can be a capacitor, even people.
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Offline hans

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Re: Apparently silicon capacitors are a thing...
« Reply #5 on: November 01, 2018, 02:31:31 pm »
Capacitors often show up as a parasitics in ICs, which is no surprise if you make metal oxides a few nm thick and bring S and D less than 20nm together. In digital ICs, often the gate capacitance of transistors is used as local supply bypassing.

But there is also effort to make capacitors in chips, but those stop at a few tenths to hundreds of pF. You could also fit a whole MCU under the same area.

Surprised that they haven't matched capacitor arrays yet. Matching in IC is usually pretty good.
 

Offline gibbled

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Re: Apparently silicon capacitors are a thing...
« Reply #6 on: November 01, 2018, 11:44:16 pm »
These look interesting too, speaking of silicon capacitors...


http://ixysic.com/Products/ProgCap.htm
 
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Offline xrunner

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Re: Apparently silicon capacitors are a thing...
« Reply #7 on: November 02, 2018, 12:09:21 am »
These look interesting too, speaking of silicon capacitors...


http://ixysic.com/Products/ProgCap.htm

Those are cool.
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Offline T3sl4co1l

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Re: Apparently silicon capacitors are a thing...
« Reply #8 on: November 02, 2018, 10:11:02 am »
I forget if they're actually silicon (MOS), or more accurately called silica glass (MOM) capacitors.

Silicon itself -- depending on doping density -- has a polarization effect, visible in the gate charge of a MOSFET for example.  Although you have to go back to old fashioned (or integrated) lateral MOS to see it, I think?  (VDMOS, most common among power transistors, either swamps or eliminates the effect, replacing it with Vds dependent capacitance instead.)  This is why SPICE has a semiconductor capacitor model, for example.

Bulk Si also has terrible resistivity (unless heavily doped), which would limit available Q more than metallization would, I think.

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Offline SiliconWizard

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