NOTES 27 March 2013Chapter 10 MOSFETS CONTINUED

MOS Structure Under Reverse Bias

2

- - - - - - - - - - - - +

-

Metal layer

Oxide layer

P-type

+ + + + + + + + + + + + +

n-type inversion layer

With large positive gate bias, there will be electrons at the interface between the oxide and semiconductor, which leads to formation of a thin n-type inversion layer

Threshold voltage VT: applied gate voltage required to achieve the threshold inversion

Voltage-Current Relationship of NMOS (1)

12

Voltage-Current Relationship of NMOS (2)

13

Saturation regionNonsaturation region

In the nonsaturation region:

In the saturation region:

2)(22 DSDSTGS

oxnD VVVV

L

CWI

2)(2 TGS

oxnD VV

L

CWI

Operation characteristics:

• No current through the gate oxide IG=0

• Current in the channel is due to drift rather than diffusion

Application: voltage controlled current source, analog switch

CMOS Technology

17

Complementary metal–oxide–semiconductor (CMOS)