Chapter 3 · Visualization 4 of 6 · Section 3.4 and Table 3.1

Region Map of the Three-Terminal Structure

Two voltages, one surface. Move the operating point in the (VCB, VGB) plane and see which region of inversion it lands in, and why.

Regions of inversion in the (VCB, VGB) plane; boundaries VL, VM, VH from Table 3.1 (amber dot: your bias)

Fixed VGB: ψS versus VCB, with the floor φ0 + VCB and the ceiling ψsa(VGB)

What to look for

weak: ψS = ΦF+VCB … 2ΦF+VCB, moderate: … +φZ, strong: above

  • Moving up (larger VGB) goes from depletion to strong inversion, as in Chapter 2.
  • Moving right (larger VCB) goes the other way: VCB alone can switch the inversion layer off.
  • The boundaries have slope slightly above 1 (about n): one more volt of VCB needs a little more than one volt of VGB.

Try this

  1. Hold VGB = 2 V and sweep VCB from 0 to 3 V. Note where each region starts and compare with VQ, VW, VU.
  2. How wide (in VGB) is weak inversion at VCB = 0? At VCB = 2 V?
  3. Make the oxide 2 nm thick. Why do the boundaries become almost parallel to the line VGB = VCB + const?
  4. On the second plot, where does ψS leave the floor and reach the ceiling?