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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?
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.
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
The blue curve in this figure shows how the capacitance varies bfore inversion and after inversion. **broken link removed**
Before inversion it decreases with thickness and afte inversion , due to the mobile carriers availble, the capacitance inreases.