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COMPARISON AND SIMULATION STUDY OF
CYLINDRICAL GAA NWMBCFET FOR SUB 35NM
S. Ashok Kumar
Research Scholar, Centre for VLSI Design, Department of Electronics and Communication Engineering,
Kalasalingam Academy of Research and Education, Virudhunagar, (India).
E-mail: 6691ashok@gmail.com
ORCID: http://orcid.org/0000-0002-0957-6685
J. Charles Pravin
Associate Professor, Centre for VLSI Design, Department of Electronics and Communication Engineering,
Kalasalingam Academy of Research and Education. Virudhunagar, (India).
E-mail: charles@klu.ac.in
ORCID: http://orcid.org/0000-0002-9009-6274
Recepción:
11/11/2019
Aceptación:
26/10/2020
Publicación:
30/11/2021
Citación sugerida:
Kumar, S. A., y Pravin, J. C. (2021). Comparison and Simulation study of Cylindrical GAA
NWMBCFET for sub 35nm. 3C Tecnología. Glosas de innovación aplicadas a la pyme, Edición Especial,
(noviembre, 2021), 199-209. https://doi.org/10.17993/3ctecno.2021.specialissue8.199-209
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Noviembre 2021
ABSTRACT
In this paper, a cylindrical Gate All Around Nano Wire Field Eect Transistor (GAA
NWFET) is compared with cylindrical Gate All Around Nano Wire Multi Bridge Channel
Field Eect Transistor (GAA NWMBCFET) for sub 35nm devices using Technology
Computer Aided Design (TCAD) simulation tool. Instead of one channel with equal
distance in vertical and horizontal stacking, about 12 thin channels have been created
in GAA NWMBCFET. The device performance has been numerically evaluated using
coupled Drift-diusion (DD) method and Shockley-Read-Hall Recombination method
(SRH). The compared transfer and output characteristics of GAA NWFET and GAA
NWMBCFET has been reported using the TCAD numerical simulation calibrations. The
inclusion of multi bridge channel in the device has increased its current drive because of
the Ultra-Thin Body (UTB). It has been accounted for that the GAA structure has a decent
insusceptibility to short channel impacts.
KEYWORDS
Cylindrical GAA NWFET, Cylindrical GAA NWMBCFET, TCAD, UTB, MBCFET.
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1. INTRODUCTION
Gate All Around structure is a promising candidate for short channel transistors as per
ITRS 2015 (ITRS version 2.0., 2015). The idea of Multi Bridge channel originates from
stacking channels one over the other. Contingent upon the quantity of channels stacked in
the transistor MBCFET ensures high output current. The output current is increased by
using Ultra-Thin Body (UTB) in the Si channel and also by reducing the oxide thickness
(Lee et al., 2003; Lee et al., 2004a).
GAA NWFET is one of the better alternatives for accomplishing superiority in Nano-level
transistors. The GAA NWFET could decrease short channel impacts like Drain Induced
Barrier Lowering (DIBL), SS and VTH roll o because of its geometric structure (Singh et
al., 2006; Al-Ameri et al., 2017). The GAA NWFET constitutes of various structures like
cubical, cylindrical and elliptical (Lin et al., 2018; Nagy et al., 2018; Salmani-Jelodar et al.,
2015). An MBCFET of 5 μm channel length was fabricated in the year 2003, and achieved
high output current of 4.6 times larger (Lee et al., 2003). In Lee et al. (2004a) an MBCFET
structure in 2004 with a reduced gate length of 250 nm was manufactured. Multi-channel
transistors were fabricated with dierent materials having gate lengths of 90nm and 30nm
as discussed in Lee et al. (2004b) and Yoon et al. (2004) respectively. All multi bridge channel
devices with enlarged width attained high output current as given in Yoon et al. (2004);
Lee et al. (2003); Lee et al. (2004b). An n-channel cylindrical structure as like in Nayak et al.
(2014), has been developed in this paper, 12 thin channels have been made rather than one
channel and every channel is encompassed by an oxide layer in TCAD.
2. DEVICE STRUCTURE
Figure 1. Cylindrical Structure formed in TCAD.
Source: own elaboration.
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The cylindrical n-channel GAA NWFET (Figure 1) is formed in TCAD by using the details
given in Nayak et al. (2014), which is detailed in Table 1. The simulation was done utilizing
the Drift-Diusion and Shockley-Read-Hall models.
A. Drift-Diusion Model
In drift-diusion model, the electron current density is:
(1)
and the current density of holes is given by:
(2)
The rst term takes into account the contribution due to the spatial variations of the
electrostatic potential, the electron anity, and the band gap. The remaining terms
consider the contribution due to the gradient of concentration, and the spatial variation of
the eective masses mn and mp. Through the Einstein relation the diusivities are derived
using the mobilities.
(3)
Table 1. Parameters and values.
Parameters Values (nm/ cm
3
)
Gate Length 35
Gate Oxide 1.5
NW Diameter 21.45
Drain/Source Doping 1e20
Channel Doping 1e15
Source: own elaboration.
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B. Shockley-Read-Hall Recombination
Recombination through deep defect levels in the gap is usually labeled SRH recombination.
In Sentaurus device, the following form is implemented:
(4)
with:
(5)
and:
(6)
where E
trap
is the dierence between the defect level and the intrinsic level. The variable
E
trap
is accessible in the parameter le. The default E
trap
value for Silicon is 0.
The doping dependence of the SRH lifetimes is modeled in Sentaurus device by use of the
Scharfetter relation:
(7)
After achieving same IV characteristics with (Nayak et al., 2014) 12 channels have been
formed in the place of single channel and the IV characteristics are measured using the
same models. The primary objective here is to increase the output current drivability of the
device without increasing the width of the transistor. The schematic of the Multi Bridge
channels in a cylindrical channel have been demonstrated in Figure 2b, 2c. The Figure 2d
shows equal distance being given to 12 channels and the electrostatic integrity has also been
maintained.
The splitted 12 thin channels are surrounded by an oxide layer. A direct metal contact on
oxide layer was given with the work function of 4.461 and a high k dielectric is used as an
oxide to control the Io value.
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(a)
(b)
(c)
(c)
Figure 2. a) Cylindrical Structure with oxide layer, b) Multi Bridge Channel, c) 12 Channels, d) Oxide layer
surrounding channels.
Source: own elaboration.
3. RESULTS
Figures 3 and 4 shows the comparison between the transfer and output characteristics of
cylindrical GAA NWFET and cylindrical GAA NWMBCFET which clearly indicates that
the Multi Bridge increases the current drivability and the short channel eects like Drain
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Induced Barrier Lowering (DIBL) and SS are reduced due to the surrounding oxide layer.
The current drive of the device was increased due to the presence of UTB Si channel,
without having to increase the width of the transistor. In transfer characteristics the curve
has been plotted for V
D
=V
G
= 1V and V
G
=50mV, V
D
=1V for both cylindrical GAA
NWFET and cylindrical GAA NWMBCFET. Figure 3 clearly shows an increase in current
drive of the GAA NWMBCFET when compared with GAA NWMBCFET. The channel
current can be increased further by reducing the oxide layer thickness but there occurs an
increase in a short channel eect Threshold voltage rollo (V
TH
rollo).
Figure 3. Compared Transfer Characteristics between GAA NWMBCFET and GAA NWFET.
Source: own elaboration.
The output characteristics are plotted by varying V
GS
from 0.7 V to 0.9 V for both devices.
By comparing the output characteristics with the GAA NWFET, the GAA NWMBCFET
clearly indicates more output current. The gate eect has been spread equivalently to all
the channels due to the presence of UTB and GAA, but it is still believed that the eect
of electro static potential will be more in outer channels than the inner channels. In Basic
GAA structure gate controls over the channels so the short channel eects will reduce but in
the case 12 channels, the inner channels not directly having contact with metal gate. That
may build the short channel impacts.
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Figure 4. Compared Output Characteristics between GAA NWMBCFET and GAA NWFET.
Source: own elaboration.
4. CONCLUSIONS
A GAA NWFET has been formed in TCAD with a gate length of 35 nm. This device
is then developed into a Nanowire Multi-Bridge-Channel FET (GAA NWMBCFET) by
splitting 12 dierent channels from the single channel, and stacking them in vertical and
horizontal manner for a gate length of 35 nm. The incorporation of Multi Bridge channels
showed an increase in current drive as compared to the normal nanowire structures. Device
performance will be varied depending upon the nanowire structure too. The proposed
MBC device displayed a maximum current drive of 65 µA, nearly 20% higher than the
conventional NWFET. By isolating the channel regions from the metal gate, by using 12
channels, the MBC structure was able to impact and alter short channel eects in such
devices. Multi bridge channels are believed to deliver exceptional performances for short
channel devices in the future and will be a potential candidate for low power applications.
5. ACKNOWLEDGEMENT
The Authors are thankful to the management of Kalasalingam Academy of Research and
Education (KARE) for the provision of TCAD laboratory facilities during this research.
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