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(mc18)
The flatband capacitance of the MOS structure at flatband is obtained by calculating the series connection of the oxide capacitance and the capacitance of the semiconductor, yielding:
(mc19
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| bet | 48/57 | | Sana | 09.05.2021 | | Hajmi | 0,62 Mb. | | #14427 |
(mc18)
The flatband capacitance of the MOS structure at flatband is obtained by calculating the series connection of the oxide capacitance and the capacitance of the semiconductor, yielding:
(mc19)
Exact analysis
For a description of the derivation of the MOS capacitance using the exact analysis we refer the reader to that section.
Deep depletion capacitance
Deep depletion occurs in an MOS capacitor when measuring the high-frequency capacitance while sweeping the gate voltage "quickly". Quickly here means that the gate voltage must be changed fast enough so that the structure is not in thermal equilibrium. One then observes that when ramping the voltage from flatband to threshold and beyond the inversion layer is not or only partially formed as the generation of minority carriers can not keep up with the amount needed to form the inversion layer. The depletion layer therefore keeps increasing beyond its maximum thermal equilibrium value, xd,T resulting in a capacitance which further decreases with voltage.
The time required to reach thermal equilibrium when abruptly biasing the MOS capacitor at a voltage larger then the threshold voltage can be estimated by taking the ratio of the total charge in the inversion layer to the thermal generation rate of minority carriers. A complete analysis should include both a surface generation rate as well as generation in the depletion layer and the quasi-neutral region. A good approximation is obtained by considering only the generation rate in the depletion region xd,dd. This yields the following equation:
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Bosh sahifa
Aloqalar
Bosh sahifa
(mc18)
The flatband capacitance of the MOS structure at flatband is obtained by calculating the series connection of the oxide capacitance and the capacitance of the semiconductor, yielding:
(mc19
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