Question

Choose the wrong one with respect to nMOSFET compared to pMOSFET

• A. ON resistance is high
• B. Size is small
• C. Junction capacitance is small
• D. Fast in operation

Hint:

nMOSFETs use electrons as majority carriers in the channel; pMOSFETs use holes.
Electrons have higher mobility than holes in silicon.
This leads to nMOSFETs generally having better performance (lower \(R_{ON}\), faster speed) than pMOSFETs of the same physical dimensions.

Answer 1

The Correct Option is A

Comparing nMOSFETs and pMOSFETs of similar dimensions: 

Electron mobility (\(\mu_n\)) is significantly higher than hole mobility (\(\mu_p\)) in silicon (\(\mu_n \approx 2-3 \times \mu_p\)).

ON resistance (\(R_{ON}\)): Since \(R_{ON}\) is inversely related to mobility, nMOSFETs have lower ON resistance than pMOSFETs of the same size. So, statement (a) "ON resistance is high" for nMOSFET compared to pMOSFET is WRONG. Incorrect

Size: For the same current driving capability (i.e., same \(R_{ON}\)), a pMOSFET needs to be larger (wider channel) than an nMOSFET. Thus, an nMOSFET can be smaller for a given performance. Statement (b) is correct for nMOSFETs. Correct

Junction capacitance: Smaller size for nMOSFETs (for same current) can lead to smaller parasitic capacitances. Statement (c) can be correct. Correct

Speed: Higher mobility in nMOSFETs leads to faster switching speeds and higher transconductance. Statement (d) is correct. Correct

\[ \boxed{\text{ON resistance is high}} \]