MOS Capacitor: A Comprehensive Overview of its Structure and Operation, Lecture notes of Fundamentals of Semiconductor Fabrication

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Modern Semiconductor Devices for Integrated Circuits (C. Hu) Slide 5-

Chapter 5 MOS Capacitor

MOS: M etal- O xide- S emiconductor

SiO (^2)

metal

gate

Si body

Vg

gate

P-body

N+

MOS capacitor MOS transistor

Vg

SiO (^2) N+

This energy-band diagram for Vg = 0 is not the simplest one.

N

+^ polysilicon

SiO

2

P-Silicon body

Chapter 5 MOS Capacitor

E f , E c

E v

E v

Si

Body

Gate

E c

E c

E v

E f

5.2 Surface Accumulation

3.1eV

Ec , Ef

Ev E 0

Ec

Ef Ev

M O S

qVg

Vox

q^ f s

Make Vg < Vfb

is negligible when the surface is in accumulation.

f (^) s : surface potential, band bending Vox : voltage across the oxide

5.2 Surface Accumulation

Gauss’s Law

V g < V t

5.3 Surface Depletion

This equation can be solved to yield f s.

5.4 Threshold Condition and Threshold Voltage

Threshold (of inversion):

n (^) s = Na , or

( Ec–Ef ) (^) surface= ( Ef – Ev ) (^) bulk , or

 A=B, and C = D (^) E

c , Ef

M O S

Ev

Ef

Ei

Ec

A

B

C = q^ fB

Ev

D

qVg =^ qVt

f st

Threshold Voltage

• for P-body,

• for N-body