High Frequency Model of Sub-100nm High-k RF CMOS

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High Frequency Model of Sub-100nm High-k RF
CMOS

• ?M. Nakagawa1, J.Song1, Y. Nara2, M. Yasuhira2,
  F. Ohtsuka2,
• T. Arikado2, K. Nakamura2, K. Kakushima1, P.
  Ahmet1, K. Tsutsui1 and H. Iwai1
• 1 Tokyo Institute of Technology,
• 4259, Nagatsuta-cho,Midoriku,Yokohama,226-8502
  Japan
• 2 Semiconductor Leading Edge Technologies,
  Inc.(SELETE),Japan
• Current affiliation Matsushita Electric
  Industrial Co.Ltd., Japan
• Current affiliation Tokyo Electron LTD., Japan

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Background RF technology
RF Technology is necessary in future ubiquitous
society and broadband society
RF CMOS can be applied
Fig.1 Application spectrum ITRS2005

• Miniaturization of MOSFET improves RF
  characteristics
• CMOS technology apply to RF application

• Low cost
• Low power dissipation and high integration

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High-k and RF CMOS
Limit of miniaturization draws near !!
One is the limit of thin film of gate insulator
Electrical isolation breaks down leading to high
dissipation
High-k insulator resolves this problem High-k is
hot technology in future MOSFET
Leakage current
But..
Concerns about High-k MOSFET in RF region
?Fall of dielectric constant in RF region
by dielectric dispersion ---
High-k is not High-k in RF region? ?Degradation
of RF characteristics
by lower mobility ? High interface
state
Dielectric dispersion
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Device structure

• HfSiON (EOT1.5nm)
• SiON (EOT1.5nm)
• Gate Length Lg
• HfSiON(64nm) SiON(51nm)
• Number of finger 12(W5µm)

Increasing gate width with multi gate finger,
the gate resistance become small
Nf Number of finger
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DC characteristics and fT, fmax
SiONL/W51nm/60mm HfSiONL/W64nm/60mm
H21dB
UgaindB

• SiON device has better DC characteristics due to
  electron mobility
• fT SiON device is higher than HfSiON device
• fmax There are little difference between two
  devices

Freq
Freq
SiON ft 155GHz HfSiON ft 131GHz
SiON fmax 53GHz HfSiON fmax 58GHz
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fT,fmax_at_Wf2um
Finger length Wf um
Morifuji, et al., VLSI technology 1999, pp 163-164

• High fmax is gotten as simulation result
  indicates
• ft grows with gate length, however fmax falls
  down with gate length

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How to estimate gate capacitance
Most simple equivalent circuit _at_Vg1.5V, Vd0V
Z11Rg1/(j?Cgategox)Rseries Cgateimag(Z11-Rg-R
series)-1
Gate capacitance is got by deembedding series
resistance from measured Z11
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High frequency gate capacitance measurement
HfSiON Lg58.6nm
SiON Lg58.6nm
10GHz
10GHz
15GHz
15GHz
20GHz
20GHz
Capacitance fF
Capacitance fF
Including overlap capacitance
VgV
10GHz
20GHz
Capacitance fF
Gate length L nm
Gate length L?L nm
VgV
Intrinsic gate capacitance

• Gate capacitance is constant at 10GHz20GHz
• Dielectric dispersion is not seen in this region

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Conclusion

• RF characteristics reflect DC characteristics
• -High electron mobility cause high fT
• fmax depend on finger length (Wf)
  -High fmax is gotten at Wf
  2um, which checks
  with simulation result
• Gate capacitance degradation due to dielectric
  dispersion is not seen at 10GHz20GHz
• High-k MOSFET has potential ability even if at RF
  region