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.
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.
Junction capacitance: Smaller size for nMOSFETs (for same current) can lead to smaller parasitic capacitances. Statement (c) can be correct.
Speed: Higher mobility in nMOSFETs leads to faster switching speeds and higher transconductance. Statement (d) is correct. The "wrong one" (incorrect statement about nMOSFETs compared to pMOSFETs) is (a). \[ \boxed{\text{ON resistance is high}} \]