Lecture 15

Ming c wu 9 vfb vgb vth deplenon if the applied gate

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Unformatted text preview: 5 – Slide 15 EE105, Fall 2013 Prof. Ming C. Wu Flatband Voltage, VFB §༊  The built- in potenNal can be “cancelled out” by applying a gate voltage that is equal in magnitude (but of the opposite polarity) as the built- in potenNal. This gate voltage is called the flatband voltage because the resulNng potenNal profile is flat. ρ ( x) x -tox 0 V ( x) x -tox 0 EE105, Fall 2013 There is no net charge (i.e. ρ(x)=0) in the semiconductor under for VGB = VFB. Lecture 15 – Slide 16 Prof. Ming C. Wu 8 Voltage Drops across a MOS Capacitor VGB − VFB = Vox + VS V ( x) -tox 0 x Xd §༊  If we know the total charge within the semiconductor (Q̕S) , we can find the electric field within the gate insulator (Eox) and hence the voltage drop across the gate insulator (Vox): ⎛ྎ − QS ⎞ྏ ʹȃ − QS ʹȃ − QS Vox = Eoxtox = ⎜ྎ E ⋅ dS = Eox A = ⎜ྎ Aε ⎟ྏtox = C ⎟ྏ ∫ ε ox ox ⎝ྎ ox ⎠ྏ where QS is the areal charge density in the semiconductor [C/cm2] and Cox ≡ ε ox t ox is the areal gate capacitance [F/cm2] Lecture 15 – Slide 17 EE105, Fall 2013 Prof. Ming C. Wu VGB < VFB (AccumulaNon) §༊  If a gate voltage more negaNve than VFB is applied, then holes will accumulate at the gate- insulator/semiconductor interface. ρ ( x) -tox x 0 V ( x) -tox x 0 EE105, Fall 2013 Areal gate charge density [C/cm2]: QG = Cox ⋅ (VGB − VFB ) Lecture 15 – Slide 18 Prof. Ming C. Wu 9 VFB < VGB < VTH (DepleNon) §༊  If the applied gate voltage is greater than VFB, then the semiconductor surface will be depleted of holes. –...
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This note was uploaded on 01/22/2014 for the course EE 105 taught by Professor King-liu during the Fall '07 term at Berkeley.

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