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IvanTheTerrible
Joined: 03 Oct 2009
Posts: 4
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 03 Oct 2009 20:17 Thickness of dielectric towards capacitance? |
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| What has the thickness of a dielectric do towards capacitance?
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katko
Joined: 22 Feb 2009
Posts: 60
Helped: 2
Location: Durham, USA
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03 Oct 2009 21:42 Thickness of dielectric towards capacitance? |
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| Please provide some context/info of any sort. Are you asking about thickness in stripline, microstrip, coax, twin line, something else, or what?
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IvanTheTerrible
Joined: 03 Oct 2009
Posts: 4
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04 Oct 2009 1:42 Re: Thickness of dielectric towards capacitance? |
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Actually I was reading about MOSFET capacitance, the gate to body of a MOSFET basically act as plates for a capacitor. During certain operating regions, a depletion region will be formed under the gate, and it can be viewed as the thickness of the dielectric of the capacitor has decreased, and so will the capacitance.
That I don't get it. How does the thickness of a dielectric relates to capacitance?
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harsha_jois
Joined: 27 Jun 2007
Posts: 56
Helped: 4
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04 Oct 2009 6:21 Thickness of dielectric towards capacitance? |
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Hello
Ivan the Terrible
The dielectric thickness controls the capacitance
as the capacitance of a capacitor is inversely proportional to the thickness. and unlike you mentioned if the thickness decreases the capacitance increases.
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04 Oct 2009 6:21 Ads |
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Colbhaidh
Joined: 10 Aug 2004
Posts: 232
Helped: 35
Location: Scotland
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12 Oct 2009 15:19 Re: Thickness of dielectric towards capacitance? |
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What you should have read was, as the depletion layer is formed beneath the gate oxide of the mosfet, the depletion layer (devoid of mobile charges and therefore essentially an insulator) increases the thickness of the effective dielectric (gate oxide plus the depletion zone) and decreases the capacitance.
This depletion zone continues to increase in thickness until and inversion layer forms in the channel imediately below the gate oxide. At this point, there is mobile charges immediately below the gate oxide and so the capacitance increases back to the original value εA/Tox
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