8/8/2019 Principles of Semiconductor Devices -Lecture37

1/29

www.nanohub.org

NCN

ECE606:SolidStateDevicesLecture37:NonidealEffectsinMOSFET

MuhammadAshrafulAlamalam@purdue.edu

1AlamECE606S09

8/8/2019 Principles of Semiconductor Devices -Lecture37

2/29

TopicMap

AlamECE606S09 2

Equilibrium DC Small

signal

Large

Signal

Circuits

Diode

Schoky

BJT/HBT

MOS

8/8/2019 Principles of Semiconductor Devices -Lecture37

3/29

Outline

AlamECE606S09 3

1. Flatbandvoltage2. ThresholdvoltageshiNduetotrappedcharges3. Physicsofinterfacetraps4. Conclusion

REF.Chapter18,SDF

8/8/2019 Principles of Semiconductor Devices -Lecture37

4/29

(1)IdealizedMOSCapacitor

AlamECE606S09 4

Substrate(p)ycs

Fm

ci

EC

EVEF

psemiconductormetal insulator

Vacuumlevel

Recallthat

8/8/2019 Principles of Semiconductor Devices -Lecture37

5/29

Poten\al,Field,Charges

AlamECE606S09 5

cs

Fm

ci

V

E

Vbi=0r

x

x

x

8/8/2019 Principles of Semiconductor Devices -Lecture37

6/29

RealMOSCapacitor withM

8/8/2019 Principles of Semiconductor Devices -Lecture37

7/29

PhysicalInterpreta\onofFlatbandVoltage

AlamECE606S09 7

flatband

EC

EV

EF

EC

EV

EF

8/8/2019 Principles of Semiconductor Devices -Lecture37

8/29

HowtoCalculateBuiltinorFlatbandVoltage

AlamECE606S09 8

cs

Fm

Vacuumlevel

EV

EF

EC

qVbi

Therefore,

8/8/2019 Principles of Semiconductor Devices -Lecture37

9/29

MeasureofFlatbandshiNfromCVCharacteris\cs

AlamECE606S09 9

C/Cox

VG

IdealVth

ActualVth

8/8/2019 Principles of Semiconductor Devices -Lecture37

10/29

Outline

AlamECE606S09 10

1. Flatbandvoltage2. VTshiHduetotrappedcharges3. Physicsofinterfacetraps4. Conclusion

8/8/2019 Principles of Semiconductor Devices -Lecture37

11/29

(2)IdealizedMOSCapacitor

AlamECE606S09 11

cs

Fm

ci

EC

EV

EF

p semiconductormetal insulator

Vacuum level

Recall that

Substrate(p)y

Qox=0

8/8/2019 Principles of Semiconductor Devices -Lecture37

12/29

DistributedTrappedchargeintheOxide

AlamECE606S09 12

EC

EV

EF

8/8/2019 Principles of Semiconductor Devices -Lecture37

13/29

AnIntui\veView

AlamECE606S09 13

Idealchargefreeoxide

E

0

Bulkcharge

E

0

E

Interfacecharge

0

Reducedgatecharge

8/8/2019 Principles of Semiconductor Devices -Lecture37

14/29

GateVoltageandOxideCharge

AlamECE606S09 14

E

0

8/8/2019 Principles of Semiconductor Devices -Lecture37

15/29

GateVoltageandOxideCharge

AlamECE606S0915

8/8/2019 Principles of Semiconductor Devices -Lecture37

16/29

Interpreta\onforBulkCharge

AlamECE606S0916

C/Cox

VG

IdealVT

ewVT

8/8/2019 Principles of Semiconductor Devices -Lecture37

17/29

Interpreta\onforInterfaceCharge

AlamECE606S0917

C/Cox

VG

IdealVT

ewVT

8/8/2019 Principles of Semiconductor Devices -Lecture37

18/29

TimedependentshiNofTrappedCharge

18

E

Sodium related bias temperature instability (BTI) issue

C/Cox

VG

IdealVT

8/8/2019 Principles of Semiconductor Devices -Lecture37

19/29

BiasTemperatureInstability(Experiment)

AlamECE606S0919

+++++

+++++

M O S

()biases

0 xo

0.1xo

x

ion

M O S

+++++

+++++

(+)biases

x

0 xo

ion

0.9xo

8/8/2019 Principles of Semiconductor Devices -Lecture37

20/29

Outline

AlamECE606S0920

1. Flatbandvoltage2. VTshiNduetotrappedcharges3. Physicsofinterfacetraps4. Conclusion

8/8/2019 Principles of Semiconductor Devices -Lecture37

21/29

SiOandSiHBonds

AlamECE606S0921

Googleimage

8/8/2019 Principles of Semiconductor Devices -Lecture37

22/29

InterfaceStates

22

HW: Unpassivated bonds ~10

14

cm

-2

8/8/2019 Principles of Semiconductor Devices -Lecture37

23/29

AnnealingofInterfaceStates

AlamECE606S0923

HH H

Forminggasanneal

8/8/2019 Principles of Semiconductor Devices -Lecture37

24/29

CVStretchOut

AlamECE606S0924

HH H

Forminggasanneal

8/8/2019 Principles of Semiconductor Devices -Lecture37

25/29

atureofDonorandAcceptorTraps

AlamECE606S0925

Acceptorlevel

eutralwhenempty

ega\vewhenfull

Donorlevel

Posi\vewhenempty

eutralwhenfull

Combina\onwhen

botharepresent

8/8/2019 Principles of Semiconductor Devices -Lecture37

26/29

DonorlikeInterfaceStates

AlamECE606S0926

C/Cox

VG

8/8/2019 Principles of Semiconductor Devices -Lecture37

27/29

8/8/2019 Principles of Semiconductor Devices -Lecture37

28/29

AcceptorandDonorTrapsCombined

AlamECE606S0928

C/Cox

VG

28

Donor-related

stretchoutAcceptor-related

stretchout

8/8/2019 Principles of Semiconductor Devices -Lecture37

29/29

Conclusion

AlamECE606S0929

1) onidealthresholdcharacteris\csareimportantconsidera\onofMOSFETdesign.

2) Thenonideali\esarisefromdifferencesingateandsubstrateworkfunc\on,trappedcharges,interface

states.

3) AlthoughnonindealeffectsoNenarisefromtransistordegrada\on,therearemanycaseswheretheseeffects

canbeusedtoenhancedesirablecharacteris\cs.