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Part 5: Quantum Effects in MOS Devices

Quantum Effects Lead to Phenomena such as:Ultra Thin Oxides – Observe:

High Leakage Currents Through the Oxide - TunnelingDepletion in Poly-Si metal gate – capacitance effectThickness of Inversion Layer – alters tox

GIDL (Gate-Induced Drain Leakage) – High Doping - Leads to tunnelingDIBL (Drain-Induced Barrier Lowering) – Short Channel - Leads to tunneling

Take advantage of Quantum EffectsDecrease effective mass

Change E -vs- k energy band diagram by…Induce strain using lattice mismatch between S/Cs

Quantum Confinement – Gain in Device EfficiencyBand gap engineering – Use other S/Cs to decrease Eg

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Part 5: Quantum Effects in MOS Devices

Ultrathin SiO2 – begin to observe quantum effects

o r o oxox

ox ox

A k AC

t t

Crystalline Si

poly-crystallineSi

p-Si Wafer

Insulator InsulatorSiO2 - Gate oxide

Source Contact Drain Contactn++ Poly Si

Gate Contact or Electrode

n+source n+drain

+

+Vgate

VDrain

channel- - -- - - -- - -- - - -

M

O

S

VSource

L

W

tox

2

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SiO2

p- Si

Ef

Part 5: Quantum Effects in MOS Devices

Ee-

n++-Si

SiO2

Flat band

p- Sin++-Si

SiO2

p- Si

n++-Si

What conditionis this?

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Part 5: Quantum Effects in MOS Devices

Ee-

SiO2

Flat band

p- Sin++-Si

SiO2

p- Si

n++-Si

What conditionis this?

Treat asIF a p-njunction

n++-Si p- Si

e- flowonly one

way

3

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Part 5: Quantum Effects in MOS Devices

n++-Si

p- Si

Polydepletion

Poly-depletion

Biased into Strong Inversion

eVRev

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Part 5: Quantum Effects in MOS DevicesDepeletion in poly-Si

Other:

Relativistic Carriers (hot emission-oxide damage)

1

,

,

1

ox

D poly

ox physical Si

C C

xC

C

Colinge & Colinge, S/C Devices

4

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Part 5: Quantum Effects in MOS DevicesQuantization: (cont.)

2D gas in channelInversion layer thickness is similar to the gate oxide thickness

Changes oxide thickness, ,

oxox eff ox physical

Si

t t x

Hareland, IEEE Transactions on Electron Devices, 1996

See also:Anderson & Anderson. Fundamentals of Semiconductor Devices, (McGraw Hill, 2005) p. 504-506

Davies, The Physics of Low Dimensional Semiconductors, (Cambridge, 1998) p. 343

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Part 5: Quantum Effects in MOS DevicesQuantization (Cont.) – Consider Quantization in MOS Channel

From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)

EC,S-C

Oxide

Semiconductor

Ee-

Where are:Ψ and lΨl2located???

5

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Part 5: Quantum Effects in MOS Devices

Quantization: Recall “Particle in a Box” or “Infinite Potential Well” or “Quantum Well”?Chapter 3 of Kasap

x = 0 x = a0

E1

E3

E2

E4

n = 1

n = 2

n = 3

n = 4

Ener

gyof

elec

tron

Energy levels in the well (x) sin(nx/a) Probability density |(x)|2

1

2

3

4

0 a a0

x

0 a x0

V(x

)

V = 0

Electron

V = 8 V = 8

Electron in a one-dimensional infinite PE well. The energy of theelectron is quantized. Possible wavefunctions and the probabilitydistributions for the electron are shown.

8

From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)

Ψ and lΨl2 is always zero at the boundary!

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Part 5: Quantum Effects in MOS DevicesQuantization: (cont.)

2D gas in channelInversion layer thickness is similar to the gate oxide thickness

Changes oxide thickness

, ,ox

ox eff ox physicalSi

t t x

Davies, The Physics of Low Dimensional Semiconductors, (Cambridge, 1998) p. 343

n ~1Energy States of e-:

Bound versus Unbound (continuum)

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Part 5: Quantum Effects in MOS DevicesTunneling:

Fowler-Nordheim (FN) [cold emission – oxides]

Direct (oxides)

Band-to-Band

Barrier lowering

Drain Induced Barrier Lowering (DIBL)

Muller & Kamins (Wiley-Interscience,2003) Fig. 9.17 p. 452Streetman & Banerjee , Solid State Electronic Circuits (Prentice Hall,2000)

This results because…

…this occurs.

p-Si Wafer

SiO2 - Gate oxide

DrainContact

Poly SiGate Contact

n+source n+drain

VdVg

Vgate= On VD=VDD

channel

DrainContact

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Part 5: Quantum Effects in MOS DevicesTunneling:

Fowler-Nordheim (FN) [cold emission – oxides]

Direct (oxides)

Band-to-Band

Barrier lowering

GIDL Sze, Modern S/C Device Physics (Wiley-Interscience,1998)Ch. 3 by SlJ. Hillenius

P-Si Wafer

SiO2 - Gate oxide

DrainContact

Poly SiGate Contact

n+source n+drain

VdVg

Vgate=0 VD=VDD

channel

DrainContact

Gate Induced Drain Leakage (GIDL)

Colinge & Colinge, S/

C Devices

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Part 5: Quantum Effects in MOS DevicesQuantization: (cont.)

2D gas in channelSOI Gate-all-around (GAA) MOSFET:

Colinge & Colinge, S/C Devices

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Part 5: Quantum Effects in MOS DevicesBandgap Engineering of ChannelConsider: Bandgap, mobility, effective mass, lattice matching, quantum confinement of carriers

From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)

Lattice Constants:aSi = 5.4309 ÅaGe = 5.6577 Å

Cullity, Elements of X-ray Diffraction, 2nd Ed (1978) Appendix 5

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Part 5: Quantum Effects in MOS DevicesBandgap Engineering of ChannelConsider: Bandgap, mobility, effective mass, lattice matching, quantum confinement of carriers

Science M. Ieong, B. Doris, J. Kedzierski, K. Rim, M. Yang, Silicon Device Scaling to Sub-10nm Regime (2004)

Lattice Constants:aSi = 5.4309 ÅaGe = 5.6577 Å

Cullity, Elements of X-ray Diffraction, 2nd Ed (1978) Appendix 5

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Part 5: Quantum Effects in MOS DevicesBandgap Engineering of ChannelConsider: Bandgap, mobility, effective mass, lattice matching, quantum confinement of carriers

IBM RJ Antoniadis et al., Continuous MOFET Performance Inc with Scaling - Strain & Channel Matl (2006)

Lattice Constants:aSi = 5.4309 ÅaGe = 5.6577 Å

Cullity, Elements of X-ray Diffraction, 2nd Ed (1978) Appendix 5

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Bandgap Engineering for Light Emitting Devices

Bandgap Engineering: Three typesNote that the band offsets are not the same!

Herbert Kroemer, Nobel Lecture: Quasielectric fields and band offsets: teaching electrons new tricks*, REVIEWS OF MODERN PHYSICS, VOLUME 73, JULY 2001, *The 2000 Nobel Prize in Physics was shared by Zhores I. Alferov, Jack S. Kilby, and Herbert Kroemer. This lecture is the text of Professor Kroemer’s address on the occasion of the award.

Anderson &

Anderson, Fundam

entals of Semiconductor D

evices, (McG

raw H

ill, 2005) Ch. 6.3 p. 317-331

Type 1 Type 2 Type 3

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Heterojunctions – Type 2 & 3

18

10

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Tunnel FET (TFET)

19IRPS Datta HTFET for Energy Efficient Computing 2013

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Tunnel FET (TFET)

20Mayberry-Intel Pushing Past Frontiers of Technology final [3 2013]

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Part 5: Quantum Effects in MOS Devices

Quantization: (cont.)

2D gas in channelSOI Gate-all-around (GAA) MOSFET:

Gate-All-Around (GAA) MOSFET is an SOI transistor in which the gate oxide and the gate electrode are wrapped around the channel region.

Fabricated using an SOI CMOS process to which two process steps are added

a photolithographic step

a wet etch step during which a cavity is formed under previously patterned silicon islands.

The remarkable features of this MOSFET are that there are two channels (at the top and the bottom of the silicon film,

The entire channel area is surrounded by good-quality gate oxide and the gate electrode.

Colinge & Colinge, S/C Devices