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

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Latent Noise in Schottky Barrier MOSFET
UPoN 2008

• Sheng-Pin Yeh, Chun-Hsing Shih, Jeng Gong, and
  Chenhsin Lien
• Institute of Electronics Engineering, National
  Tsing Hua University, Taiwan
• Department of Electrical Engineering, Yuan Ze
  University, Taiwan
• Email chshih_at_saturn.yzu.edu.tw

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Latent Noise in Schottky Barrier MOSFET

• Necessity of Metallic Source/Drain
• I-V Curves of SBMOS
• Noise in SBMOS and MOSFET
• Latent Noise Mechanisms in SBMOS
• Summary

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Necessity of Metallic Source/Drain
Gate Length
SDE Resistance
SDE Depth
Source ITRS
Unacceptable SDE resistance will limit the use of
impurity doped S/D
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Recent 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.
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Latent Noise in Schottky Barrier MOSFET

• Necessity of Metallic Source/Drain
• I-V Curves of SBMOS
• Noise in SBMOS and MOSFET
• Latent Noise Mechanisms in SBMOS
• Summary

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SBMOS vs. MOSFET (Drain Current)
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.
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SBMOS vs. MOSFET (Energy Band Diagrams)
SBMOS
MOSFET
Thermal Emission
Vg 0V
Vg 0V
e-
e-
fBn
Vg 1V
Vg 1V
SB Tunneling
Vd 1V
Vd 1V
In SBMOS, carriers can thermonicly emit over or
laterally tunnel through Schottky barrier to
contribute drain current. Unique Impact
Ionization is observed in SBMOS.
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Ambipolar Conduction
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.
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Dopant Segregated Schottky Barrier MOSFET
(DS-SBMOS)
Inserting a heavily doped segregation layer
effectively modifies the Schottky barriers to
increase the driving current and suppress the
ambipolar behavior.
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Interface States Generated during Metal
Silicidation
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
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Latent Noise in Schottky Barrier MOSFET

• Necessity of Metallic Source/Drain
• I-V Curves of SBMOS
• Noise in SBMOS and MOSFET
• Latent Noise Mechanisms in SBMOS
• Summary

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Noise in Conventional MOSFETs

• For MOSFETs
• Drain current fluctuates due to variations of
• Number of inversion charge density ?Qi lttraps
  in gate oxidegt
• (and number of inversion carriers in channel
  ?NWL? Qi)
• Effective channel mobility ?µeff ltphonon
  scatteringgt

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Unique Noise in Schottky Barrier MOSFET
NMOS, p-Si
T. Asano, Jpn. J. Appl. Phys., 2002, p. 2306.
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)
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Unique Noise in Schottky Barrier MOSFET (Cont.)
PMOS
M. V. Haartman, ICNF 2005, p. 307.
Observations 1. More Noisy in SBMOS (PMOS), SBH
NiSi 0.45 eV for hole 2. Strong dependence of
noise on gate bias
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Latent Noise in Schottky Barrier MOSFET

• Necessity of Metallic Source/Drain
• I-V Curves of SBMOS
• Noise in SBMOS and MOSFET
• Latent Noise Mechanisms in SBMOS
• Summary

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Noise Mechanisms in SBMOS at Silicon Surface
Mechanisms 1. Number Fluctuation lttraps in gate
oxidegt 2. Mobility Fluctuation ltphonon
scatteringgt 3. But with unique impact ionization
in Source
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Noise Mechanisms in SBMOS at Source
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
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Noise 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.
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Noise Problems in SBMOS
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Summary

• Eliminating the limits on the dopant junctions
  makes SBMOS as one of the most attracting
  candidates for future CMOS devices, while SBMOS
  suffers from potential problems on its unique
  Schottky barrier junctions.
• Schottky barrier MOSFETs present particular
  ambipolar conduction as a function of gate
  voltage.
• Formation of the metallic source/drain using
  metals silicidation brings about interface states
  and noise sources.
• Unique noises in SBMOS were observed. Proposed
  noise mechanisms in SBMOS are presented.
• Proper noise behavior and mechanisms in SBMOS
  require further thorough investigations.