MOSFET

If the gate insulator of an nMOSFET is made thicker with all else unchanged, how does the magnitude of the threshold voltage generally change?

  1. AIt becomes zero
  2. BIt becomes larger
  3. CIt becomes smaller
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Answer: B. It becomes larger

A thicker gate insulator reduces the gate capacitance Cox, so a larger gate voltage is needed to support the same depletion charge. The magnitude of the threshold voltage therefore increases. High-voltage transistors with thick oxide, used in I/O circuits, also tend to have higher threshold voltages.

  • A. Oxide thickness alone does not make the threshold voltage zero.
  • B. Correct. Cox decreases, so the required gate voltage rises.
  • C. A thinner insulator tends to reduce the threshold voltage.
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More MOSFET questions

  1. Which generally describes the relationship between a MOSFET's gate length (the length of the gate electrode on the mask or after patterning) and its effective channel length?
  2. Which correctly describes punch-through in a MOSFET?
  3. In a pass transistor (switch) made of a single nMOSFET with its gate at the supply voltage VDD, how high does the output rise when passing an input of VDD?
  4. In a CMOS inverter, what is the current that flows from the supply to ground while the input is switching called?
  5. Power MOSFETs are easy to use in parallel. Which statement about the temperature dependence of on-resistance explains why?