L. Head//ECE Dept./Rowan University

Engineering Engineering Electromagnetics 1Electromagnetics 1

0909.301.010909.301.01 Fall 2004Fall 2004

Linda HeadECE Department

Rowan University

http://engineering.rowan.edu/~shreek/fall04/eemag1/lectures/mosfets.ppt

INTRODUCTION TO MOSFETSINTRODUCTION TO MOSFETSOctober 6, 2004October 6, 2004

L. Head//ECE Dept./Rowan University

Silicon - Four CasesSilicon - Four Cases

Si

Si Si

Si

Intrinsic Si - 0oK

P-type Si N-type Si

Si

Si Si

Si

h+ e -

Intrinsic Si - Room Temp

Si

Si Si

B-

h+

e -h+

Si

Si Si

+

e -

Ph

h+ e -

L. Head//ECE Dept./Rowan University

Metal-Oxide-SemiconductorMetal-Oxide-SemiconductorCapacitorCapacitor

Metal SiO2

n+ polysilicon

p-type silicon

L. Head//ECE Dept./Rowan University

Looks Like…….Looks Like…….Insulator

Conductor

Conductor

L. Head//ECE Dept./Rowan University

The positive charge on the metal is matched by negative charge from the ions in the p-type semiconductor. The h+ just get pushed away from the interface between the insulator and the p-type semiconductor leaving only the “stuck” charged atoms. We call this the depletion region - we now have a 2-layer insulator.

+V

SiO2

Metal and Polysilicon

p-type Si

Gnd.

L. Head//ECE Dept./Rowan University

Once a maximum width is reached for the “depletion region” the electrons in the material are attracted to the SiO2 / p-type Si interface and now there is an channel of electrons right underneath the SiO2

++V

SiO2

Metal and Polysilicon

p-type Si

Gnd.

Electron Channel

L. Head//ECE Dept./Rowan University

MOSFET Operating RegionsMOSFET Operating Regions

L. Head//ECE Dept./Rowan University

Depletion RegionDepletion Region

Al

Al

Aln+ Polysilicon

Si Si

Si

0.4 V 0 V

L. Head//ECE Dept./Rowan University

Inversion Region Inversion Region 1.0 V 0 V0 V

L. Head//ECE Dept./Rowan University

Linear RegionLinear Region0.25 V1 V

L. Head//ECE Dept./Rowan University

Pinch-Off RegionPinch-Off Region1 V 1.5 V

L. Head//ECE Dept./Rowan University

Things You Need To KnowThings You Need To Know

r(Si) = 11.8 r(SiO2) = 3.9

• The length of the “channel” is 1.

• The n+ source and drain, the polysilicon and the p+ semiconductor are metal-like conductors.