SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

9.3. METAL-OXIDE-SEMICONDUCTOR CAPACITOR 443

Ec

Ei

EF

Ev

M

O Semiconductor

EF

eVG

W

d

z

Charge density

under inversion

Qm Q (charge per unit area)

Qd: charge from background dopants

Qn: free carrier charge

W

z

Electric

field

Electrostatic

potential

W

z

Es

Eox

z

V(x)

W

V

Vs

VG = Vfb + V

= Vfb + Vox + Vs

Vox

Band profile

under inversion

Metal-insulator

interface

Figure 9.10: A schematic of the distributions of charge, electric field, and electrostatic potential
in the ideal MOS capacitor in inversion.Onceinversionbegins,thedepletionwidthWdoesnot
increasefurtherbecauseofthehighmobileelectrondensityattheinterfaceregion.