GATE EC 2015 Set 2 — Question 54
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Electronic Devices → MOS Capacitor & MOSFET → C-V Characteristics
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Question
In a MOS capacitor with an oxide layer thickness of , the maximum depletion layer thickness is . The permittivities of the semiconductor and the oxide layer are and respectively. Assuming , the ratio of the maximum capacitance to the minimum capacitance of this MOS capacitor is _______.
Correct answer
4.3 to 4.4
Solution
The maximum capacitance occurs in accumulation and is equal to the oxide capacitance:
The minimum capacitance occurs at maximum depletion and is the series combination of and the maximum depletion capacitance :
where The ratio is:
Substitute the expressions for and :
Given , , and :
Therefore:
The minimum capacitance occurs at maximum depletion and is the series combination of and the maximum depletion capacitance :
where The ratio is:
Substitute the expressions for and :
Given , , and :
Therefore:
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