Latent Noise in Schottky Barrier MOSFET

Latent Noise in Schottky Barrier MOSFET UPoN 20081

Latent Noise in Schottky Barrier MOSFETLatent Noise in Schottky Barrier MOSFET

Sheng-Pin Yeh, Sheng-Pin Yeh, Chun-Hsing ShihChun-Hsing Shih*, Jeng Gong, and Chenhsin Lien*, Jeng Gong, and Chenhsin Lien

Institute of Electronics Engineering, National Tsing Hua University, Taiwan Institute of Electronics Engineering, National Tsing Hua University, Taiwan

*Department of Electrical Engineering, Yuan Ze University, Taiwan*Department of Electrical Engineering, Yuan Ze University, Taiwan

*Email: [email protected]*Email: [email protected]

UPoN 2008UPoN 2008



Necessity of Metallic Source/DrainNecessity of Metallic Source/Drain

I-V Curves of SBMOSI-V Curves of SBMOS

Noise in SBMOS and MOSFET Noise in SBMOS and MOSFET

Latent Noise Mechanisms in SBMOSLatent Noise Mechanisms in SBMOS

SummarySummary



Source: ITRS

Gate Length

SDE Depth

SDE Resistance

Xj

Rsd

Gate

S/D

Unacceptable SDE resistance will limit the use of impurity doped S/D


Recent Research of SBMOSRecent Research of SBMOS

Eliminating the limits on the dopant source/drain junctions makes metallic S/D SBMOS as one of the most attracting candidates for use in future CMOS devices.





Noise in SBMOS and MOSFETNoise in SBMOS and MOSFET


SummarySummary


SBMOS vs. MOSFET (Drain Current)SBMOS vs. MOSFET (Drain Current)

Gate

n+ Source

n+ Drain

Silicon Substrate

Gate Oxide

Conventional

MOSFET

Gate

Schottky Source

Schottky Drain

Silicon Substrate

Gate Oxide

SBMOS

Lg = 90 nm, Tox = 2.5 nm, SBH = 0.4 eV

SBMOS suffers from potential constraints on the drain currents because of its

unique Schottky barrier source/drain junctions.


SBMOS vs. MOSFET (Energy Band Diagrams)SBMOS vs. MOSFET (Energy Band Diagrams)

Gate

n+ Source

n+ Drain

Silicon Substrate

Gate Oxide

Gate

Schottky Source

Schottky Drain

Silicon Substrate

Gate Oxide

Vg= 0V

Vg= 1V

Vd= 1V

e-

SBMOS MOSFET

φBn

Vg= 0V

Vg= 1V

Vd= 1V

e-

In SBMOS, carriers can thermonicly emit over or laterally tunnel through Schottky barrier to contribute drain current. Unique Impact Ionization is observed in SBMOS.

SB Tunneling

Thermal Emission


Ambipolar Conduction Ambipolar Conduction

-1.0 -0.5 0.0 0.5 1.0 1.5 2.010-12

10-10

10-8

10-6

10-4

10-2

Dra

in C

urr

ent (

A/

m)

Gate Bias (V)

Lg = 90 nm, Tox = 2.5 nm

Vd = 1.0 V

φ Bn = 0.5 eV

φ Bn = 0 eV

φ Bp = 0.6 eV

φ Bp = 1.1 eV

SBMOS presents the ambipolar conduction as a function of gate voltage. At a negative bias, holes can also pass through the drain Schottky barrier, forming a hole channel, yielding an undesirable drain current. And, SBH must be minimized.


Dopant Segregated Schottky Barrier MOSFET (DS-SBMOS)Dopant Segregated Schottky Barrier MOSFET (DS-SBMOS)

SBMOS

Off-State (Vg = -0.5 V) On-State (Vg = 1.0 V)

Source

Drain

electron

hole

(Vd = 1.0V)

DS-SBMOS

```

DS-SBMOS

Schottky Source

Schottky Drain

Dopant Segregated Layer

Inserting a heavily doped segregation layer effectively modifies the Schottky barriers to increase the driving current and suppress the ambipolar behavior.


Interface States Generated during Metal SilicidationInterface States Generated during Metal Silicidation

φ Bn

Interface States EC

EF

EV

EFi Schottky Source Si

Vg

Electron

Si

Silicide

Interface

Metal

Metal Diffusion

Si

Si Diffusion

Metal

Si

Dopant Segregation

Metal

Dopant

Si

Drain

Formation of the metallic source/drain using silicidation brings about interface states and noise sources. Importantly, trap and detrap depend on Vg and SBH.

Hole





Noise in SBMOS and MOSFETNoise in SBMOS and MOSFET


SummarySummary


NoiseNoise in Conventional MOSFETs in Conventional MOSFETs

For MOSFETs For MOSFETs

Drain current fluctuates due to variations ofDrain current fluctuates due to variations of

Number of inversion charge density ∆Qi <traps in gate oxide>

(and number of inversion carriers in channel ∆N=WL∆ Qi)

Effective channel mobility ∆μeff <phonon scattering>

dsieffd VQL

WI

effeff

di

i

dd

IQ

Q

II

Oxide Traps

Source

Drain

e-

e- e

-

e-

e- e

-

e-

e-

e-

e- e

-

Scattering

Gate


Unique Noise in Schottky Barrier MOSFETUnique Noise in Schottky Barrier MOSFET

T. Asano, Jpn. J. Appl. Phys.,

2002, p. 2306.

NMOS, p-Si

Observations:

1. More Noisy in SBMOS than MOSFET

2. Unique noise observed in different metals silicidation SBMOS

(SBH: PtSi = 0.85 eV, NiSi = 0.65 eV for electron)


Unique Noise in Schottky Barrier MOSFET (Cont.)Unique Noise in Schottky Barrier MOSFET (Cont.)

M. V. Haartman, ICNF 2005, p. 307.

PMOS

Observations:

1. More Noisy in SBMOS (PMOS), SBH: NiSi = 0.45 eV for hole

2. Strong dependence of noise on gate bias





Noise in SBMOS and MOSFET Noise in SBMOS and MOSFET


SummarySummary


Noise Mechanisms in SBMOS: at Silicon SurfaceNoise Mechanisms in SBMOS: at Silicon Surface

Oxide Traps

Schottky Barrier

Source

Schottky Barrier

Drain

e- e-

e-

e- e-

e- e- e- e- e-

e-

Dopant Segregated Layer (If applied)

Scattering

Gate

φBn

Vg= 0V

Vg= 1V

Vd= 1V

e-

Mechanisms:

1. Number Fluctuation 1. Number Fluctuation <<traps in gate oxidetraps in gate oxide>>

2. Mobility Fluctuation 2. Mobility Fluctuation <<phonon scatteringphonon scattering>>3. But with unique impact ionization in Source3. But with unique impact ionization in Source


Noise Mechanisms in SBMOS: at SourceNoise Mechanisms in SBMOS: at Source

Schottky Barrier

Source

Gate

Mechanisms:

1. Trap levels in Schottky barrier contact

(SBH and Gate bias dependent)

2. Trap levels in substrate metallic Source contact

(SBH and substrate bias dependent)

3. Different in DS-SBMOS and SBMOS

φBn

InterfaceStates EC

EF

EV

EFiSchottkySource Si

Vg

SourceSource


Noise Mechanisms in SBMOS: at DrainNoise Mechanisms in SBMOS: at Drain

Mechanisms:

1. Trap levels in channel and substrate metallic (Schottky barrier) contact (SBH and bias dependent)

2. Noise generations in Drain is different to those in Source due to ambipolar conduction.

Source

e-

Source

e-

Drainh+

Drainh+

Schottky Barrier

Source

Schottky Barrier

Drain


Gate

Surface channel


Noise Problems in SBMOSNoise Problems in SBMOS

Oxide Traps

Schottky Barrier

Source

Schottky Barrier

Drain

e- e-

e- e- e-

e- e- e- e- e-

e-

Drain

e-

Source Impact Ionization

e-

Source

e-

Source

e-

Drainh+

Drainh+


III

III

IV

IV

I

I

V II

II V

SourceSource

(If no DS layer) (If no DS layer)

Schottky barrier MOSFET

Conventional MOSFET

Drain


SummarySummary

Eliminating the limits on the dopant junctions makes SBMOS as one of Eliminating the limits on the dopant junctions makes SBMOS as one of

the most attracting candidates for future CMOS devices, while the most attracting candidates for future CMOS devices, while SBMOS SBMOS

suffers from potential suffers from potential problemsproblems onon its unique Schottky barrier junctions its unique Schottky barrier junctions..

Schottky barrier MOSFETs present particular ambipolar conduction as Schottky barrier MOSFETs present particular ambipolar conduction as

a function of gate voltage.a function of gate voltage.

Formation of the metallic source/drain using metals silicidation brings Formation of the metallic source/drain using metals silicidation brings

about interface states and noise sources.about interface states and noise sources.

Unique noises in SBMOS were observed. Proposed noise mechanisms in Unique noises in SBMOS were observed. Proposed noise mechanisms in

SBMOS are presented. SBMOS are presented.

Proper noise behavior and mechanisms in SBMOS require further Proper noise behavior and mechanisms in SBMOS require further

thorough investigations.thorough investigations.

Latent Noise in Schottky Barrier MOSFET

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