MOSFET

In a short-channel MOSFET, what is the main reason the drain current falls below the (VGS − Vth) square law and approaches a linear dependence?

  1. ABody bias effect
  2. BIncrease in gate capacitance
  3. CCarrier velocity saturation
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Answer: C. Carrier velocity saturation

As the channel gets shorter, the electric field in the channel becomes stronger, and carrier velocity reaches its upper limit (saturation velocity). Raising the gate voltage then does not increase current as much as the square law predicts, and the dependence approaches the first power of (VGS − Vth).

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