MOSFET

Which correctly describes punch-through in a MOSFET?

  1. AA drop in channel mobility with temperature
  2. BThe source and drain depletion layers merge and current flows that the gate cannot control
  3. CDielectric breakdown of the gate insulator
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Answer: B. The source and drain depletion layers merge and current flows that the gate cannot control

With a short channel and lightly doped substrate, raising the drain voltage can make the drain depletion layer merge with the source depletion layer. Current then flows deep in the substrate regardless of the gate, and the transistor cannot be turned off. This is called punch-through.

  • A. The temperature dependence of mobility is not punch-through.
  • B. Correct. The depletion layers merge and uncontrollable current flows.
  • C. Insulator breakdown is gate oxide breakdown, a different phenomenon.
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More MOSFET questions

  1. 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?
  2. In a CMOS inverter, what is the current that flows from the supply to ground while the input is switching called?
  3. Power MOSFETs are easy to use in parallel. Which statement about the temperature dependence of on-resistance explains why?
  4. Under Dennard (constant-field) scaling, which statement is correct when dimensions and voltages are each scaled by 1/k?
  5. Which correctly describes the flat-band voltage of a MOS structure?