mosfet operation

Animation of the MOSFET manufacturing process

I encourage you to look at the website given below and use the button

“animate to next” – the actual process is described for each step.

http://jas.eng.buffalo.edu/education/fab/NMOS/nmos.html

Basic structure of the MOSFETp type substrate

W

oxide

L

metal

+n

source draingate

+n

+n is a heavily doped n type semiconductorbody

4 terminal devicetypically grounded

Basic idea of the MOSFET

p+n

S DG

+n

GSV

DI

channel region

contains electrons

DSV

ground

ground

- -

E

Electron motion

is governed by a

perpendicular

electric field!

is controlled by D GSI V

MOS capacitor p type semiconductorvoltage bias effects –battery switched

oxide

oxide

AC

t

G

oxide

VE

toxt oxGV E

2

2

( ) ( ) ( )

s

d V x x dE x

dxdx

GV

MOSFET p type semiconductor gate voltage VG > VT

cE

vE

FxE

FiE

FmE

G TV V

electrons

- - - - -

+ + + + +E

G

DS

L

NMOS -- p type semiconductor -- gate voltage VG variable - circuit models

GV

S

G

DD

S

G

D

S

G

L

PMOS -- n type semiconductor -- gate voltage VG variable - circuit models

GV

S

G

DD

S

G

D

S

G

L

NMOS & PMOSNMOS – n channel in a p-type semiconductor

PMOS – p channel in an n-type semiconductor

D

S

GB

D

S

GB

S

G

D

B

- +

NMOS -- p type semiconductor -- gate voltage VGS < VT

GV

G

S D+n+nspace charge region-

L

NMOS -- p type semiconductor -- gate voltage VGS > VT

space charge region

GV

G

S D+n+n

inversion layer

--

DI

L

D d DSI g V

d n nW

g QL

Derivation of the conductance

Dd

DS

Ig

V

n n

DS

v Q W

E L

n DS n

DS

E Q W

E L

GV

G

S D+n+n

DI

L

NMOS -- p type semiconductor -- gate voltage VGS > VT – long channel

GV

G

S D+n+n

D d DSI g VDI

d n nW

g QL

n oxide GS TNQ C V V

D n oxide GS TN DSW

I C V V VL

L

NMOS -- p type semiconductor – VGS > VT & changing VDS

GV

G

S D+n+n

linear regionDI saturation

> saturation

DI

DSV

DS GS TNV saturation V V

electric field

Typical characteristics

2

DSD n oxide GS TN DS

VWI C V V V

L 2

Biasing effects N channel MOSFEThttp://www.mtmi.vu.lt/pfk/funkc_dariniai/transistor/mosfet.htm

depletion mode

enhancement mode

Simple three-dimensional unit cell

a

b

c