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Design and Performance Analysis of 20nm Si/Ge
channel Pentagonal and Trapezoidal Nanowire
Transistors
Submitted by :
JAIDEV
ECE 1312088
Under the guidance of :
Dr. S. S. Gill
(Hod of ECE department)
Prof. Navneet Kaur
Outline
1. Introduction
2. Literature Review
3. Objectives & Methodology
4. Present work
5. Results
6. Conclusion and Future Work
7. References
1. Introduction
• The downscaling of planar transistors has brought several
detrimental effects such as increment of leakage currents and
Short Channel Effects.
• For this reason, a large number of novel structures have been
proposed to enhance performance, such as Schottky barrier
(SB) MOSFETs (Park et al., 2002), Fin-FET (Chauan et al.,
2010) and GAA silicon nanowire transistors (NWTs) (Zang et
al., 2010).
• Among these devices, NWTs with Gate-All-Around (GAA)
structure are reported to have the best gate controllability over
channel.
• With better suppression of SCEs, NWTs can offer lower
leakage current and higher on–off current ratio.
2. Nanowire Process Parameters
• Figure 1.1 Schematic structure of GAA SiNWT.
• The performance of the NanoWire is determine in large
part by its process parameters. The key process
parameter in the design of the Nano Wire are:
• D: Diameter of silicon, defined by the distance in
between gate oxides.
• H: Height of silicon, defined by the distance between top
and bottom.
• 𝑇𝑜𝑥 : Gate oxide thickness, defined by the distance between
Channel and gate;
• Doping concentration of channel and Source/Drain contact
region.
• Ls/d : Length of Source and drain respectively.
Figure 1.2 Schematic representations of (a) Circular NWTs, (b) Triangular NWTs,
(c) Cross sections of CNWTs and (d) Cross section of TNWTs.
• Gate Length (Lg): This process parameter determine the
technology of the device.
• With the reduction in gate length the transistor switching
speed increase and also its dimension reduces allowing us to
have more number of transistor on the same area.
• However with this reduction short channel effects also
increases.
 Cross section shapes of nanowire: Up to now, Triangular, circular
and rectangular shape nanowires have been used in FET.
Figure 1.3 Schematic representations of (a) Rectangular NWTs, (b) Circular NWTs,
(c) Triangular NWTs.
2. Literature Review
H. Xuan et al. [2014] in the paper “Performance Studies in Nanowire
Field-Effect Transistors with Different Cross Sections” investigated
SNWTs with three different cross sections (triangular, circular and
square) and have simulated through TCAD and their performance
parameters are studied. The SNWT with triangular cross section exhibits
higher Ion/Ioff ratio, better subthreshold characteristics and have been
compared with other transistors. In addition, an equivalent model have
been proposed to accurately estimate the performance of different
shaped SNWTs with the same channel cross-section area to simplify the
device model for future circuit simulation
Zang et al. [2014] in the paper entitled “Comparative study of silicon
nanowire transistors with triangular-shaped cross sections” presented
Nanowire transistors with triangular cross sections (TNWTs) are
proposed and studied. Working mechanisms of TNWTs and impacts of
physical parameters are investigated with technology computer aided
design (TCAD) tools. It is found that TNWT’s current mostly
concentrates in channel center, and expands to corners of the triangle at
a higher gate voltage. TNWTs with a longer channel length show better
subthreshold slope and lower drain-induced barrier lowering (DIBL),
which allows low gate work function to be maintained.
R. Gupta et al. [2014] in the paper “Study of Gate all around lnAs/Si
based Nanowire FETs using Simulation Approach,” presented a GAA
Si Nanowire FET (SNWFET) and InAs NWFET and compared it with
respect to various performance parameters. The device metrics
considered at the nanometer scale are transfer characteristics,
transconductance, output characteristics, drive and leakage current,
switching speed (Ion/Ioft), conduction band profile, subthreshold
swing and DlBL. It is shown that InAs channelled NWFET have
higher mobility and hence higher transconductance, whereas Si
NWFET shows better immunity towards SCE with lower leakage
current, lower subthreshold slope, lower DlBL.
Sleight et al. (2010) in the paper entitled “Gate-All-Around Silicon Nanowire
MOSFETs and Circuits” demonstrated undoped-body, GAA NWFETs with
excellent electrostatic scaling. They have observed the clearly scaling SCEs
versus NW size. Additionally, they have observed a divergence of NW
capacitance device self-heating for very smaller diameter.
Chen and Tan (2014) in the paper entitled of “Modeling and Analysis of Gate-
All-Around Silicon Nanowire FET” is presented GAA SiCNWT and
equivalent FinFET. They have simulated these device by TCAD and
compared them. In this paper they have analyzed the electrical characteristics
like carrier transportation, induced stress effect and self-heating effect.
3. Problem Formulation
• The continued scaling of modern MOSFETs has increased both
the packing density and the speed of modern ICs.
• However, the reduction of channel length below a critical
dimension often leads to a commensurate increase in the short
channel effects (SCEs), such as drain-induced barrier lowering
(DIBL) .
• A number of technologies, such as, Silicon-On- Insulator (SOI)
and multi-gate device structures (e.g., FINFET) have been
introduced to improve gate control and suppress SCEs.
Contd…
• Among them, Nanowire (NW) Gate-all-around (GAA) MOSFET
is considered a leading candidate to address the scaling
challenges below 20nm technology nodes, because of its
excellent SCE immunity and low source-drain leakage current.
• With a number of high-mobility n-channel InGaAs NWs
configured in parallel, such GAA transistors can already satisfy
the target ITRS requirement for the ON current, with excellent
on-off ratio.
4. Objectives
The proposed objectives of this thesis are
1. To Design Si/Ge based 20nm Pentagonal and Trapezoidal Nanowire
Transistors for different process parameters like Diameter and
Height.
2. To evaluate and analyse the device performance in terms of transfer
characteristics, output characteristics and SCE like DIBL and
Subthreshold Swing for Different Process Parameters.
3. To Compare these results with 20 nm triangular FET.
Methodology
To achieve above objectives the following steps will be followed:-
• Different cross sections NWFETs nanowire will be studied.
• Trapezoidal NWT and PNWT will be designed for 20 nm
technology.
• Varying the top width with keeping constant height and bottom
width such that the shape of Triangular NWT will change from
triangular to trapezoidal.
• Varying the bottom width and one base corner angle with
keeping constant height such that the shape of trapezoidal
nanowire will change from trapezoidal to pentagonal.
• Transfer characteristics, output characteristics and SCEs like SS
and DIBL will be evaluated for different Diameter (D).
• The step 2 and 3 will be repeated for different height and
different channel materials (Si and Ge).
• The effects of the different process parameters on the
performance of 20 nm PNWT and TrNWT will be analysed.
.
SOFTWARE TO BE USED
TCAD (Technology Computer Aided Design)
PLACE OF WORK
Fibre Optics & Research Lab, Guru Nanak Dev Engineering
College, Ludhiana.
4. Present work
Triangular NWTs
Figure 4.1 Schematic representations of Triangular NWT.
No. Doping Region Concentration
1 Substrate 2e17
2 Source/drain 2.063e20
3 Channel 1e15
Table 4.1 Doping Concentration in NWTs.
10nm
8nm 10nm 12nm 14nm
8nm 10nm 12nm 14nm 8nm
Trapezoidal NanoWire FET
Figure 4.2 Schematic representation of Pentagonal NWT.
Figure 4.3 Pentagonal cross section shapes with different diameter and heights.
8nm 10nm 12nm 14nm
8nm 10nm 12nm 14nm
Figure 4.4 Schematic representation of trapezoidal NWT.
Figure4.5 Pentagonal cross section shapes with different diameter and
heights.
5. Results and Conclusions
Pentagonal SiNWT
Figure 5.1 Simulated (a) transfer characteristics in linear and logarithmic scales and (b)
output characteristics of Pentagonal SiNWT for Lg=20nm.
(a) (b)
No. Cross section
shape
Ion ( A) Ioff (A) Ion/Ioff Cross
section
area
1 Trapezoidal 5.4000e-5 1.3878e-10 3.89e5 80
2 Pentagonal 4.7206e-5 1.0102e-10 4.67e5 75
3 Triangular 4.6570e-5 7.1315e-11 6.19e5 50
Table5.1 Extracted values from transfer characteristics of different shapes NWTs
Trapezoidal SiNWT
Figure 5.2 Simulated (a) transfer characteristics in linear and logarithmic scales and (b)
output characteristics of Trapezoidal SiNWT for Lg=20nm.
(a)
(a)
(b)
Triangular SiNWT
Figure 5.3 Simulated (a) transfer characteristics in linear and logarithmic scales and (b)
output characteristics of Triangular SiNWT for Lg=20nm.
(a) (b)
No. Cross section
shape
Ion ( A) Ioff (A) Ion/Ioff Cross
section area
1 Trapezoidal 3.83e-5 5.47e-13 7.00e7 80
2 Pentagonal 2.88e-5 4.02e-13 7.162e7 75
3 Triangular 2.84e-5 3.82e-13 7.434e7 50
Table 5.2 Extracted values from transfer characteristics of different shapes GeNWTs.
Pentagonal GeNWT
Figure 5.4 Simulated (a) transfer characteristics in linear and logarithmic scales and (b)
output characteristics of Pentagonal GeNWT for Lg=20nm.
(a) (b)
Trapezoidal GeNWT
Figure 5.5 Simulated (a) transfer characteristics in linear and logarithmic scales and (b)
output characteristics of Trapezoidal GeNWT for Lg=20nm.
Triangular GeNWT
Figure 5.6 Simulated (a) transfer characteristics in linear and logarithmic scales and (b)
output characteristics of Trapezoidal GeNWT for Lg=20nm.
No. Crose section shape Ion ( A) Ioff (A) Ion/Ioff Cross section
area
1 Trapezoidal 6.5681e-5 8.8291e-11 7.439e5 80
2 Pentagonal 5.186 e-5 6.5714e-11 7.890e5 75
3 Triangular 5.046e-5 5.9156e-11 8.539e5 50
4 Triangular ( according
to base paper)
10.5e-6 2.61e-12 4.01e6 50
Table 5.3. Ion (A) of SiNWT with different cross sections.
(a) (b)
Figure 5.7(a) Ion of SiNWT (b) Ion of GeNWT.
No. Cross section
shape
Ion ( A) Ioff (A) Ion/Ioff Cross section
area
1 Trapezoidal 3.83e-5 5.47e-13 7.00e7 80
2 Pentagonal 2.88e-5 4.02e-13 7.162e7 75
3 Triangular 2.84e-5 3.82e-13 7.434e7 50
Table 5.4. Ion (A) of GeNWT with different cross sections.
(a) (b)
Figure 5.8 (a) Ion/Ioff Ratio of SiNWT (b) Ion/Ioff Ratio of GeNWT.
No. SHAPE SS (mV/dec)
1 Triangular ( according to base paper) 64
2 Triangular 63.7
3 Trapezoidal 63
4 Pentagonal 62.2
Table 5.5. Subthreshol Swing of SiNWT with different cross sections.
Figure 5.9 (a) Subthreshold Swing (mV/dec) of SiNWT (b) SS (mV/dec) of GeNWT with different
cross sections.
No. SHAPE SS (mV/dec)
1 Triangular 65.1
2 Trapezoidal 63.4
3 Pentagonal 63
Table 5.6 Subthreshold Swing of GeNWT with different cross sections.
No. SHAPE DIBL (mV/V)
1 Triangular ( according to base paper) 14
2 Triangular 14
3 Trapezoidal 12
4 Pentagonal 10
Table 5.7 DIBL of SiNWT with different cross sections.
(a) (b)
Figure 5.10 (a) DIBL (mV/V) of SiNWT (b) DIBL (mV/V) of GeNWT.
No. SHAPE DIBL(mV/V)
1 Triangular 13
2 Trapezoidal 12
3 Pentagonal 11
Table 5.8 DIBL of GeNWT with different cross sections.
No. SHAPE Vti (V)
1 Triangular ( according to base paper) 0.3100
2 Triangular 0.2366
3 Pentagonal 0.2294
4 Trapezoidal 0.2285
Table 5.9. Vti of SiNWT with different cross sections.
(a) (b)
Figure 5.11 (a) Vti(V) of SiNWT (b) Vti(V)of GeNWT with different cross sections.
No. SHAPE Vti (V)
1 Triangular 0.4317
2 Pentagonal 0.4228
3 Trapezoidal 0.4217
Table 5.10 Vti of GeNWT with different cross sections.
6nm 8nm 10nm 12nm
Ioff 6.61e-13 4.276e-13 2.983e-13 1.7625e-13
Ion 3.80e-5 3.806e-5 4.955e-5 5.3230e-5
Ion/Ioff ratio 8.90e7 8.900e7 1.66e8 3.028e8
Table 5.11 Ion and Ion/Ioff ratio of Ge PNWT with different diameters.
Figure 5.12 Ion (A) of Pentagonal GeNWT with different diameters.
Figure 5.13 Ion/Ioff ratio of Pentagonal GeNWT with different diameters.
6nm 8nm 10nm 12nm
Ioff 1.25e-13 1.889e-13 2.983e-13 2.3376e-13
Ion 3.70e-5 4.7304e-5 4.955e-5 5.024e-5
Ion/Ioff ratio 2.96e8 2.508e8 1.66e8 2.149e8
Table 5.12 Ion and Ion/Ioff ratio of Ge PNWT with different Heights.
Figure 5.14 Ion (A) of Pentagonal GeNWT with different heights.
Figure 5.15 Ion/Ioff Ratio of Pentagonal GeNWT with different heights.
6nm 8nm 10nm 12nm
Ioff 5.21e-13 5.418e-13 5.47e-13 5.75e-13
Ion 2.01e-5 2.300e-5 6.549e-5 7.24e-5
Ion/Ioff ratio 3.868e7 4.245e7 1.197e8 1.25e8
Table 5.13 Ion and Ion/Ioff ratio of Ge TrNWT with different diameters.
Figure 1.16 Ion (A) of Trapezoidal GeNWT with different Diameters.
Figure 5.17 Ion/Ioff Ratio of Trapezoidal GeNWT with different Diameters.
6nm 8nm 10nm 12nm
Ioff 3.42e-13 6.1480e-13 5.47e-13 4.9013e-13
Ion 2.66e-5 4.046e-05 6.549e-5 7.4235e-5
Ion/Ioff ratio 7.77e7 6.58e7 1.19e8 1.51e8
Table 5.14 Ion and Ion/Ioff ratio of Ge TrNWT with different heights.
Figure 5.18 Ion (A) of Trapezoidal GeNWT with different heights.
Figure 5.19 Ion/Ioff Ratio of Trapezoidal GeNWT with different heights.
6nm 8nm 10nm 12nm
Ioff 3.69e11 4.980e-11 7.941e-11 1.065e-10
Ion 5.62e-05 5.923e-5 7.698e-5 7.9712e-5
Ion/Ioff ratio 1.520e6 1.18e6 9.68e5 7.48e5
Table 5.15 Ion and Ion/Ioff ratio of Ge PNWT with different diameters.
Figure 5.20 Ion (A) of Pentagonal SiNWT with different Diameters.
Figure 5.21 Ion/Ioff ratio of Pentagonal SiNWT with different diameters.
6nm 8nm 10nm 12nm
Ioff 4.85e11 1.2916-13 7.941e-11 9.33e-11
Ion 5.68e-5 6.7197e-5 7.698e-5 7.9031e-5
Ion/Ioff ratio 1.17e6 5.20e8 9.68e5 8.47e5
Table 5.16 Ion and Ion/Ioff ratio of Si PNWT with different heights.
Figure 5.22 Ion (A) of Pentagonal SiNWT with different heights.
Figure 5.23 Ion/Ioff ratio of Pentagonal SiNWT with different heights.
6nm 8nm 10nm 12nm
Ioff 1.06e-10 1.130e-10 8.82e-11 2.40e-10
Ion 3.15e-5 3.54e-05 9.408e-5 10.49e-5
Ion/Ioff ratio 2.97e5 3.13e5 1.06e6 4.37e5
Table 5.17 Ion and Ion/Ioff ratio of Si TrNWT with different diameters.
Figure 5.24 Ion (A) of Trapezoidal SiNWT with different diameters.
Figure 5.25 Ion/Ioff Ratio of Trapezoidal SiNWT with different diameters.
6nm 8nm 10nm 12nm
Ioff 4.17e-11 7.40e-11 8.82e-11 1.1029e-10
Ion 4.388e-5 5.972e-5 9.408e-5 10.79e-5
Ion/Ioff ratio 1.05e6 8.06e5 1.06e6 9.7912e5
Table 5.18 Ion and Ion/Ioff ratio of Ge PNWT with different heights.
Figure 5.26 Ion (A) of Trapezoidal SiNWT with different Heights.
Figure 5.27 Ion/Ioff ratio of Trapezoidal SiNWT with different Heights.
Diameter (nm) Pentagonal Trapezoidal
6 61.5 63
8 62 64
10 63 63.4
12 63.6 67.8
Table 5.19 Subthreshold Swing of Pentagonal and Trapezoidal GeNWT with different diameters.
Figure 5.28 Subthreshold Swing of Pentagonal and Trapezoidal GeNWT with different
diameters.
Height (nm) Pentagonal trapezoidal
6 61.8 62
8 62.5 63.3
10 63 63.4
12 62.5 63.5
Table 5.20 Subthreshold Swing of Pentagonal and Trapezoidal GeNWT with different heights.
Figure 5.29 The Subthreshold Swing of Pentagonal and Trapezoidal GeNWT with different
heights.
Diameter (nm) Pentagonal trapezoidal
6 61.5 62.8
8 61.4 62.9
10 62.2 63.0
12 62.8 66.2
Table 5.21 Subthreshold Swing of Pentagonal and Trapezoidal SiNWT with different Diameters.
Figure 5.30 Subthreshold Swing of Pentagonal and Trapezoidal SiNWT with different
diameters.
Height (nm) Pentagonal trapezoidal
6 61.7 62
8 62.4 62.8
10 62.2 63
12 61.5 63.3
Table 5.22 Subthreshold Swing of Pentagonal and Trapezoidal SiNWT with different heights.
Figure 5.31 Subthreshold Swing of Pentagonal and Trapezoidal SiNWT with different
heights.
Diameter (nm) Pentagonal trapezoidal
6 10.3 11.4
8 10.5 11.7
10 11 12
12 11.2 12.5
Table 5.23 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal GeNWT with different diameters.
Figure 5.32 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal GeNWT with
different diameters.
Height (nm) Pentagonal trapezoidal
6 10.5 11
8 10.8 11.8
10 11 12
12 10.9 12.6
Table 5.24 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal GeNWT with different heights.
Figure 5.33 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal GeNWT with
different Heights.
Diameter (nm) Pentagonal trapezoidal
6 9.6 10.3
8 9.9 11
10 10 12
12 10.5 12.4
Table 5.25 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal SiNWT with different diameters.
Figure 5.34 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal SiNWT with
different diameters.
Height (nm) Pentagonal trapezoidal
6 9.5 10.4
8 9.7 11
10 10 12
12 10.3 12.4
Table 5.26 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal SiNWT with different heights.
Figure 5.35 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal SiNWT with
different heights.
Conclusions
GAA NWT with different channel materials (Ge and Si) and with different
cross section shapes like Triangular, Trapezoidal and pentagonal was
designed and analysed for 20nm technology.
• The performance of all these GAA structures have analysed in term of
output characteristics, transfer characteristics, Ion current, Ion/Ioff ratio
and SCEs like Subthreshold Swing and Drain Induced Barrier Lowering.
• It was found that pentagonal cross shape NWT can improved the
electrical results. PNWT have better performance in terms of SCEs like
SS and DIBL and optimum Ion current and Ion/Ioff ratio.
• Whereas Si Trapezoidal NWTs have shown maximum Ion current
because of maximum conducting area. But due to losses of gate
controllability, it have maximum SCEs.
• Triangular NWT have good controllability due to the corner effects so it
have less SECs than TrNWTs.
• In this work, Silicon NWTs have better Ion and better SCEs than Ge.
• But Ge have shown better Ion/Ioff ratio and better performance in terms
of leakage current.
• I have analysed the electrical characteristics with different height and
diameters.
• Pentagonal SiNWT with 6nm diameter have minimum SS (61.5 mV/V)
that is very close to ideal value of SS (60mV/V) for short channel
devices (20 nm gate length). I have obtained improved results from my
base paper TNWT.
Cont…
PNWT vs TNWT / TrNWT Base paper
Ion Si +2.89 % than TNWT
-21% than TrNWT
+5 times
Ge +1.40% than TNWT
-24% than TrNWT
+3 times
Ion/ioff Si -7.50% than TNWT
+6.04% than TrNWT
-4 times
Ge -3.63% than TNWT
+2.28% than TrNWT
17 times
SS Si -2.35% than TNWT
-1.26% than TrNWT
-0.49%
Ge -3.22% than TNWT
-0.63% than TrNWT
-1.56%
DIBL Si -28% than TNWT
-16% than TrNWT
same
Ge -15% than TNWT
-8.33% than TrNWT
-21%
Vti Si -3.04% than TNWT
+0.39% than TrNWT
-26%
Ge -2.06% than TNWT
+0.26% than TrNWT
+36.38%
Table 6.1 A comparative analysis of PNWT vs TNWT and TrNWT.
In future these all devices could be used in single chip and make it
more functional and multipurpose chip. There could be used more
other cross section shapes like hexagonal, octagonal and could be
improved Ion current for high power applications. Future work
could be done with new materials such as SiGe NW channel and
compound semiconductor NW channel with high-k dielectrics.
There could be designed with other orientation like 110 and 111
according to application.
Future work
References
1. Charis, A. M. (2011), “Fifty Years of Moore’s Law”, IEEE TRANSACTIONS on Semiconductor
Manufacturing, vol.24, 2, May 2011.
2. Yu, W., Zhang, B., Durgun, E., Minamisawa, R. A., Luptak, R., Hagedorn, M., Holländer, B.,
Schubert, J., Hartmann, J.M., Bourdelle, K.K., Zhao, Q.T., Buca1, D. and Mant, S. (2010), “High
Mobility Si-Ge Channels And Novel High-K Materials For Nanomosfets”, IEEE
TRANSACTIONS on Electron Device, vol. 13, 5, June 2010.
3. Park, J. and Colinge, J. P. (2002), “Multiple-Gate SOI MOSFETs: Device Design Guidelines”, IEEE
TRANSACTIONS on Electron Devices, vol. 49, 12, December 2002.
4. Suzuki, K. and Pidin, S. (2003), “Short-Channel Single-Gate SOI MOSFET Model”, IEEE
TRANSACTIONS on Electron Devices, vol. 50, 5, May 2003.
5. Wong, H. S., David J. F. and Solomon, P. M. (1998), “Device Design Considerations for Double-
Gate, Ground-Plane, and Single-Gated Ultra-Thin SOI MOSFET's at the 25 nm Chnnel Length
Generation”,
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Ultimate DGMOSFET”, IEEE TRANSACTIONS on Electron Devices, vol. 53, 4, April 2006.
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Gate-All-Around Silicon MOSFETs for 6-T SRAM Area Efficiency and Yield”, IEEE
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Thank you

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GAA nano wire FET

  • 1. Design and Performance Analysis of 20nm Si/Ge channel Pentagonal and Trapezoidal Nanowire Transistors Submitted by : JAIDEV ECE 1312088 Under the guidance of : Dr. S. S. Gill (Hod of ECE department) Prof. Navneet Kaur
  • 2. Outline 1. Introduction 2. Literature Review 3. Objectives & Methodology 4. Present work 5. Results 6. Conclusion and Future Work 7. References
  • 3. 1. Introduction • The downscaling of planar transistors has brought several detrimental effects such as increment of leakage currents and Short Channel Effects. • For this reason, a large number of novel structures have been proposed to enhance performance, such as Schottky barrier (SB) MOSFETs (Park et al., 2002), Fin-FET (Chauan et al., 2010) and GAA silicon nanowire transistors (NWTs) (Zang et al., 2010). • Among these devices, NWTs with Gate-All-Around (GAA) structure are reported to have the best gate controllability over channel. • With better suppression of SCEs, NWTs can offer lower leakage current and higher on–off current ratio.
  • 4. 2. Nanowire Process Parameters • Figure 1.1 Schematic structure of GAA SiNWT. • The performance of the NanoWire is determine in large part by its process parameters. The key process parameter in the design of the Nano Wire are: • D: Diameter of silicon, defined by the distance in between gate oxides. • H: Height of silicon, defined by the distance between top and bottom.
  • 5. • 𝑇𝑜𝑥 : Gate oxide thickness, defined by the distance between Channel and gate; • Doping concentration of channel and Source/Drain contact region. • Ls/d : Length of Source and drain respectively. Figure 1.2 Schematic representations of (a) Circular NWTs, (b) Triangular NWTs, (c) Cross sections of CNWTs and (d) Cross section of TNWTs.
  • 6. • Gate Length (Lg): This process parameter determine the technology of the device. • With the reduction in gate length the transistor switching speed increase and also its dimension reduces allowing us to have more number of transistor on the same area. • However with this reduction short channel effects also increases.
  • 7.  Cross section shapes of nanowire: Up to now, Triangular, circular and rectangular shape nanowires have been used in FET. Figure 1.3 Schematic representations of (a) Rectangular NWTs, (b) Circular NWTs, (c) Triangular NWTs.
  • 8. 2. Literature Review H. Xuan et al. [2014] in the paper “Performance Studies in Nanowire Field-Effect Transistors with Different Cross Sections” investigated SNWTs with three different cross sections (triangular, circular and square) and have simulated through TCAD and their performance parameters are studied. The SNWT with triangular cross section exhibits higher Ion/Ioff ratio, better subthreshold characteristics and have been compared with other transistors. In addition, an equivalent model have been proposed to accurately estimate the performance of different shaped SNWTs with the same channel cross-section area to simplify the device model for future circuit simulation
  • 9. Zang et al. [2014] in the paper entitled “Comparative study of silicon nanowire transistors with triangular-shaped cross sections” presented Nanowire transistors with triangular cross sections (TNWTs) are proposed and studied. Working mechanisms of TNWTs and impacts of physical parameters are investigated with technology computer aided design (TCAD) tools. It is found that TNWT’s current mostly concentrates in channel center, and expands to corners of the triangle at a higher gate voltage. TNWTs with a longer channel length show better subthreshold slope and lower drain-induced barrier lowering (DIBL), which allows low gate work function to be maintained.
  • 10. R. Gupta et al. [2014] in the paper “Study of Gate all around lnAs/Si based Nanowire FETs using Simulation Approach,” presented a GAA Si Nanowire FET (SNWFET) and InAs NWFET and compared it with respect to various performance parameters. The device metrics considered at the nanometer scale are transfer characteristics, transconductance, output characteristics, drive and leakage current, switching speed (Ion/Ioft), conduction band profile, subthreshold swing and DlBL. It is shown that InAs channelled NWFET have higher mobility and hence higher transconductance, whereas Si NWFET shows better immunity towards SCE with lower leakage current, lower subthreshold slope, lower DlBL.
  • 11. Sleight et al. (2010) in the paper entitled “Gate-All-Around Silicon Nanowire MOSFETs and Circuits” demonstrated undoped-body, GAA NWFETs with excellent electrostatic scaling. They have observed the clearly scaling SCEs versus NW size. Additionally, they have observed a divergence of NW capacitance device self-heating for very smaller diameter. Chen and Tan (2014) in the paper entitled of “Modeling and Analysis of Gate- All-Around Silicon Nanowire FET” is presented GAA SiCNWT and equivalent FinFET. They have simulated these device by TCAD and compared them. In this paper they have analyzed the electrical characteristics like carrier transportation, induced stress effect and self-heating effect.
  • 12. 3. Problem Formulation • The continued scaling of modern MOSFETs has increased both the packing density and the speed of modern ICs. • However, the reduction of channel length below a critical dimension often leads to a commensurate increase in the short channel effects (SCEs), such as drain-induced barrier lowering (DIBL) . • A number of technologies, such as, Silicon-On- Insulator (SOI) and multi-gate device structures (e.g., FINFET) have been introduced to improve gate control and suppress SCEs.
  • 13. Contd… • Among them, Nanowire (NW) Gate-all-around (GAA) MOSFET is considered a leading candidate to address the scaling challenges below 20nm technology nodes, because of its excellent SCE immunity and low source-drain leakage current. • With a number of high-mobility n-channel InGaAs NWs configured in parallel, such GAA transistors can already satisfy the target ITRS requirement for the ON current, with excellent on-off ratio.
  • 14. 4. Objectives The proposed objectives of this thesis are 1. To Design Si/Ge based 20nm Pentagonal and Trapezoidal Nanowire Transistors for different process parameters like Diameter and Height. 2. To evaluate and analyse the device performance in terms of transfer characteristics, output characteristics and SCE like DIBL and Subthreshold Swing for Different Process Parameters. 3. To Compare these results with 20 nm triangular FET.
  • 15. Methodology To achieve above objectives the following steps will be followed:- • Different cross sections NWFETs nanowire will be studied. • Trapezoidal NWT and PNWT will be designed for 20 nm technology. • Varying the top width with keeping constant height and bottom width such that the shape of Triangular NWT will change from triangular to trapezoidal.
  • 16. • Varying the bottom width and one base corner angle with keeping constant height such that the shape of trapezoidal nanowire will change from trapezoidal to pentagonal. • Transfer characteristics, output characteristics and SCEs like SS and DIBL will be evaluated for different Diameter (D). • The step 2 and 3 will be repeated for different height and different channel materials (Si and Ge). • The effects of the different process parameters on the performance of 20 nm PNWT and TrNWT will be analysed. .
  • 17. SOFTWARE TO BE USED TCAD (Technology Computer Aided Design) PLACE OF WORK Fibre Optics & Research Lab, Guru Nanak Dev Engineering College, Ludhiana.
  • 18. 4. Present work Triangular NWTs Figure 4.1 Schematic representations of Triangular NWT. No. Doping Region Concentration 1 Substrate 2e17 2 Source/drain 2.063e20 3 Channel 1e15 Table 4.1 Doping Concentration in NWTs.
  • 19. 10nm 8nm 10nm 12nm 14nm 8nm 10nm 12nm 14nm 8nm Trapezoidal NanoWire FET Figure 4.2 Schematic representation of Pentagonal NWT. Figure 4.3 Pentagonal cross section shapes with different diameter and heights.
  • 20. 8nm 10nm 12nm 14nm 8nm 10nm 12nm 14nm Figure 4.4 Schematic representation of trapezoidal NWT. Figure4.5 Pentagonal cross section shapes with different diameter and heights.
  • 21. 5. Results and Conclusions Pentagonal SiNWT Figure 5.1 Simulated (a) transfer characteristics in linear and logarithmic scales and (b) output characteristics of Pentagonal SiNWT for Lg=20nm. (a) (b) No. Cross section shape Ion ( A) Ioff (A) Ion/Ioff Cross section area 1 Trapezoidal 5.4000e-5 1.3878e-10 3.89e5 80 2 Pentagonal 4.7206e-5 1.0102e-10 4.67e5 75 3 Triangular 4.6570e-5 7.1315e-11 6.19e5 50 Table5.1 Extracted values from transfer characteristics of different shapes NWTs
  • 22. Trapezoidal SiNWT Figure 5.2 Simulated (a) transfer characteristics in linear and logarithmic scales and (b) output characteristics of Trapezoidal SiNWT for Lg=20nm. (a) (a) (b)
  • 23. Triangular SiNWT Figure 5.3 Simulated (a) transfer characteristics in linear and logarithmic scales and (b) output characteristics of Triangular SiNWT for Lg=20nm. (a) (b)
  • 24. No. Cross section shape Ion ( A) Ioff (A) Ion/Ioff Cross section area 1 Trapezoidal 3.83e-5 5.47e-13 7.00e7 80 2 Pentagonal 2.88e-5 4.02e-13 7.162e7 75 3 Triangular 2.84e-5 3.82e-13 7.434e7 50 Table 5.2 Extracted values from transfer characteristics of different shapes GeNWTs. Pentagonal GeNWT Figure 5.4 Simulated (a) transfer characteristics in linear and logarithmic scales and (b) output characteristics of Pentagonal GeNWT for Lg=20nm. (a) (b)
  • 25. Trapezoidal GeNWT Figure 5.5 Simulated (a) transfer characteristics in linear and logarithmic scales and (b) output characteristics of Trapezoidal GeNWT for Lg=20nm.
  • 26. Triangular GeNWT Figure 5.6 Simulated (a) transfer characteristics in linear and logarithmic scales and (b) output characteristics of Trapezoidal GeNWT for Lg=20nm.
  • 27. No. Crose section shape Ion ( A) Ioff (A) Ion/Ioff Cross section area 1 Trapezoidal 6.5681e-5 8.8291e-11 7.439e5 80 2 Pentagonal 5.186 e-5 6.5714e-11 7.890e5 75 3 Triangular 5.046e-5 5.9156e-11 8.539e5 50 4 Triangular ( according to base paper) 10.5e-6 2.61e-12 4.01e6 50 Table 5.3. Ion (A) of SiNWT with different cross sections. (a) (b) Figure 5.7(a) Ion of SiNWT (b) Ion of GeNWT.
  • 28. No. Cross section shape Ion ( A) Ioff (A) Ion/Ioff Cross section area 1 Trapezoidal 3.83e-5 5.47e-13 7.00e7 80 2 Pentagonal 2.88e-5 4.02e-13 7.162e7 75 3 Triangular 2.84e-5 3.82e-13 7.434e7 50 Table 5.4. Ion (A) of GeNWT with different cross sections. (a) (b) Figure 5.8 (a) Ion/Ioff Ratio of SiNWT (b) Ion/Ioff Ratio of GeNWT.
  • 29. No. SHAPE SS (mV/dec) 1 Triangular ( according to base paper) 64 2 Triangular 63.7 3 Trapezoidal 63 4 Pentagonal 62.2 Table 5.5. Subthreshol Swing of SiNWT with different cross sections. Figure 5.9 (a) Subthreshold Swing (mV/dec) of SiNWT (b) SS (mV/dec) of GeNWT with different cross sections. No. SHAPE SS (mV/dec) 1 Triangular 65.1 2 Trapezoidal 63.4 3 Pentagonal 63 Table 5.6 Subthreshold Swing of GeNWT with different cross sections.
  • 30. No. SHAPE DIBL (mV/V) 1 Triangular ( according to base paper) 14 2 Triangular 14 3 Trapezoidal 12 4 Pentagonal 10 Table 5.7 DIBL of SiNWT with different cross sections. (a) (b) Figure 5.10 (a) DIBL (mV/V) of SiNWT (b) DIBL (mV/V) of GeNWT. No. SHAPE DIBL(mV/V) 1 Triangular 13 2 Trapezoidal 12 3 Pentagonal 11 Table 5.8 DIBL of GeNWT with different cross sections.
  • 31. No. SHAPE Vti (V) 1 Triangular ( according to base paper) 0.3100 2 Triangular 0.2366 3 Pentagonal 0.2294 4 Trapezoidal 0.2285 Table 5.9. Vti of SiNWT with different cross sections. (a) (b) Figure 5.11 (a) Vti(V) of SiNWT (b) Vti(V)of GeNWT with different cross sections. No. SHAPE Vti (V) 1 Triangular 0.4317 2 Pentagonal 0.4228 3 Trapezoidal 0.4217 Table 5.10 Vti of GeNWT with different cross sections.
  • 32. 6nm 8nm 10nm 12nm Ioff 6.61e-13 4.276e-13 2.983e-13 1.7625e-13 Ion 3.80e-5 3.806e-5 4.955e-5 5.3230e-5 Ion/Ioff ratio 8.90e7 8.900e7 1.66e8 3.028e8 Table 5.11 Ion and Ion/Ioff ratio of Ge PNWT with different diameters. Figure 5.12 Ion (A) of Pentagonal GeNWT with different diameters. Figure 5.13 Ion/Ioff ratio of Pentagonal GeNWT with different diameters.
  • 33. 6nm 8nm 10nm 12nm Ioff 1.25e-13 1.889e-13 2.983e-13 2.3376e-13 Ion 3.70e-5 4.7304e-5 4.955e-5 5.024e-5 Ion/Ioff ratio 2.96e8 2.508e8 1.66e8 2.149e8 Table 5.12 Ion and Ion/Ioff ratio of Ge PNWT with different Heights. Figure 5.14 Ion (A) of Pentagonal GeNWT with different heights. Figure 5.15 Ion/Ioff Ratio of Pentagonal GeNWT with different heights.
  • 34. 6nm 8nm 10nm 12nm Ioff 5.21e-13 5.418e-13 5.47e-13 5.75e-13 Ion 2.01e-5 2.300e-5 6.549e-5 7.24e-5 Ion/Ioff ratio 3.868e7 4.245e7 1.197e8 1.25e8 Table 5.13 Ion and Ion/Ioff ratio of Ge TrNWT with different diameters. Figure 1.16 Ion (A) of Trapezoidal GeNWT with different Diameters. Figure 5.17 Ion/Ioff Ratio of Trapezoidal GeNWT with different Diameters.
  • 35. 6nm 8nm 10nm 12nm Ioff 3.42e-13 6.1480e-13 5.47e-13 4.9013e-13 Ion 2.66e-5 4.046e-05 6.549e-5 7.4235e-5 Ion/Ioff ratio 7.77e7 6.58e7 1.19e8 1.51e8 Table 5.14 Ion and Ion/Ioff ratio of Ge TrNWT with different heights. Figure 5.18 Ion (A) of Trapezoidal GeNWT with different heights. Figure 5.19 Ion/Ioff Ratio of Trapezoidal GeNWT with different heights.
  • 36. 6nm 8nm 10nm 12nm Ioff 3.69e11 4.980e-11 7.941e-11 1.065e-10 Ion 5.62e-05 5.923e-5 7.698e-5 7.9712e-5 Ion/Ioff ratio 1.520e6 1.18e6 9.68e5 7.48e5 Table 5.15 Ion and Ion/Ioff ratio of Ge PNWT with different diameters. Figure 5.20 Ion (A) of Pentagonal SiNWT with different Diameters. Figure 5.21 Ion/Ioff ratio of Pentagonal SiNWT with different diameters.
  • 37. 6nm 8nm 10nm 12nm Ioff 4.85e11 1.2916-13 7.941e-11 9.33e-11 Ion 5.68e-5 6.7197e-5 7.698e-5 7.9031e-5 Ion/Ioff ratio 1.17e6 5.20e8 9.68e5 8.47e5 Table 5.16 Ion and Ion/Ioff ratio of Si PNWT with different heights. Figure 5.22 Ion (A) of Pentagonal SiNWT with different heights. Figure 5.23 Ion/Ioff ratio of Pentagonal SiNWT with different heights.
  • 38. 6nm 8nm 10nm 12nm Ioff 1.06e-10 1.130e-10 8.82e-11 2.40e-10 Ion 3.15e-5 3.54e-05 9.408e-5 10.49e-5 Ion/Ioff ratio 2.97e5 3.13e5 1.06e6 4.37e5 Table 5.17 Ion and Ion/Ioff ratio of Si TrNWT with different diameters. Figure 5.24 Ion (A) of Trapezoidal SiNWT with different diameters. Figure 5.25 Ion/Ioff Ratio of Trapezoidal SiNWT with different diameters.
  • 39. 6nm 8nm 10nm 12nm Ioff 4.17e-11 7.40e-11 8.82e-11 1.1029e-10 Ion 4.388e-5 5.972e-5 9.408e-5 10.79e-5 Ion/Ioff ratio 1.05e6 8.06e5 1.06e6 9.7912e5 Table 5.18 Ion and Ion/Ioff ratio of Ge PNWT with different heights. Figure 5.26 Ion (A) of Trapezoidal SiNWT with different Heights. Figure 5.27 Ion/Ioff ratio of Trapezoidal SiNWT with different Heights.
  • 40. Diameter (nm) Pentagonal Trapezoidal 6 61.5 63 8 62 64 10 63 63.4 12 63.6 67.8 Table 5.19 Subthreshold Swing of Pentagonal and Trapezoidal GeNWT with different diameters. Figure 5.28 Subthreshold Swing of Pentagonal and Trapezoidal GeNWT with different diameters.
  • 41. Height (nm) Pentagonal trapezoidal 6 61.8 62 8 62.5 63.3 10 63 63.4 12 62.5 63.5 Table 5.20 Subthreshold Swing of Pentagonal and Trapezoidal GeNWT with different heights. Figure 5.29 The Subthreshold Swing of Pentagonal and Trapezoidal GeNWT with different heights.
  • 42. Diameter (nm) Pentagonal trapezoidal 6 61.5 62.8 8 61.4 62.9 10 62.2 63.0 12 62.8 66.2 Table 5.21 Subthreshold Swing of Pentagonal and Trapezoidal SiNWT with different Diameters. Figure 5.30 Subthreshold Swing of Pentagonal and Trapezoidal SiNWT with different diameters.
  • 43. Height (nm) Pentagonal trapezoidal 6 61.7 62 8 62.4 62.8 10 62.2 63 12 61.5 63.3 Table 5.22 Subthreshold Swing of Pentagonal and Trapezoidal SiNWT with different heights. Figure 5.31 Subthreshold Swing of Pentagonal and Trapezoidal SiNWT with different heights.
  • 44. Diameter (nm) Pentagonal trapezoidal 6 10.3 11.4 8 10.5 11.7 10 11 12 12 11.2 12.5 Table 5.23 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal GeNWT with different diameters. Figure 5.32 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal GeNWT with different diameters.
  • 45. Height (nm) Pentagonal trapezoidal 6 10.5 11 8 10.8 11.8 10 11 12 12 10.9 12.6 Table 5.24 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal GeNWT with different heights. Figure 5.33 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal GeNWT with different Heights.
  • 46. Diameter (nm) Pentagonal trapezoidal 6 9.6 10.3 8 9.9 11 10 10 12 12 10.5 12.4 Table 5.25 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal SiNWT with different diameters. Figure 5.34 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal SiNWT with different diameters.
  • 47. Height (nm) Pentagonal trapezoidal 6 9.5 10.4 8 9.7 11 10 10 12 12 10.3 12.4 Table 5.26 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal SiNWT with different heights. Figure 5.35 Drain Induced Barrier Lowering of Pentagonal and Trapezoidal SiNWT with different heights.
  • 48. Conclusions GAA NWT with different channel materials (Ge and Si) and with different cross section shapes like Triangular, Trapezoidal and pentagonal was designed and analysed for 20nm technology. • The performance of all these GAA structures have analysed in term of output characteristics, transfer characteristics, Ion current, Ion/Ioff ratio and SCEs like Subthreshold Swing and Drain Induced Barrier Lowering. • It was found that pentagonal cross shape NWT can improved the electrical results. PNWT have better performance in terms of SCEs like SS and DIBL and optimum Ion current and Ion/Ioff ratio. • Whereas Si Trapezoidal NWTs have shown maximum Ion current because of maximum conducting area. But due to losses of gate controllability, it have maximum SCEs.
  • 49. • Triangular NWT have good controllability due to the corner effects so it have less SECs than TrNWTs. • In this work, Silicon NWTs have better Ion and better SCEs than Ge. • But Ge have shown better Ion/Ioff ratio and better performance in terms of leakage current. • I have analysed the electrical characteristics with different height and diameters. • Pentagonal SiNWT with 6nm diameter have minimum SS (61.5 mV/V) that is very close to ideal value of SS (60mV/V) for short channel devices (20 nm gate length). I have obtained improved results from my base paper TNWT. Cont…
  • 50. PNWT vs TNWT / TrNWT Base paper Ion Si +2.89 % than TNWT -21% than TrNWT +5 times Ge +1.40% than TNWT -24% than TrNWT +3 times Ion/ioff Si -7.50% than TNWT +6.04% than TrNWT -4 times Ge -3.63% than TNWT +2.28% than TrNWT 17 times SS Si -2.35% than TNWT -1.26% than TrNWT -0.49% Ge -3.22% than TNWT -0.63% than TrNWT -1.56% DIBL Si -28% than TNWT -16% than TrNWT same Ge -15% than TNWT -8.33% than TrNWT -21% Vti Si -3.04% than TNWT +0.39% than TrNWT -26% Ge -2.06% than TNWT +0.26% than TrNWT +36.38% Table 6.1 A comparative analysis of PNWT vs TNWT and TrNWT.
  • 51. In future these all devices could be used in single chip and make it more functional and multipurpose chip. There could be used more other cross section shapes like hexagonal, octagonal and could be improved Ion current for high power applications. Future work could be done with new materials such as SiGe NW channel and compound semiconductor NW channel with high-k dielectrics. There could be designed with other orientation like 110 and 111 according to application. Future work
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