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GATE 2014 EC (EC1) – Question 20

Electronic Devices · P-N Junction and Semiconductor Devices · 1 mark · Multiple choice

Fixed positive charges in the gate oxide of an n-channel enhancement MOSFET lead to ______.

  1. decreased threshold voltage
  2. channel length modulation
  3. increased substrate leakage current
  4. increased accumulation capacitance

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Correct answer: (A) decreased threshold voltage

Explanation

Positive fixed oxide charge assists the positive gate voltage in creating electron inversion at the silicon surface. Less applied gate voltage is therefore needed. Quantitatively the threshold shift is ΔVT=−Qox/Cox, which is negative for positive Qox. Thus the NMOS threshold voltage **decreases,A**.