DESIGN AND INVESTIGATION OF SIGE HETEROJUNCTION BASED CHARGE PLASMA VERTICAL TFET FOR BIOSENSING APPLICATION
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https://doi.org/10.1007/s12633-021-01384-x
ORIGINAL PAPER
Design and Investigation of SiGe Heterojunction Based Charge
Plasma Vertical TFET for Biosensing Application
Shailendra Singh 1 & Amit Kumar Singh Chauhan 2 & Gaurish Joshi 2 & Jeetendra Singh 3
Received: 13 August 2021 / Accepted: 10 September 2021
# Springer Nature B.V. 2021
Abstract
This paper explores the Vertical tunnel FET with the introduced layer of SiGe within the channel/source junction using TCAD.
As Tunnel FETs smothered the 60 mV/decade confinement level through the utilization of quantum-mechanical B2BT to
enhance this circuit’s efficiency for low-power applications. The vertical analysis of the source channel and drain will enhance
the scalability of the device. Moreover, integration of 2 nm pocket Silicon germanium layer into the channel leads to aggressive
improvements in VT numerical simulations, Subthreshold swing (SS) found to be 29.07 mV/decade, high on/off current ratio of
109 in 50 nm channel. To avoid the problem like random dopant fluctuation (RDF), this draft deals with the doping charge plasma
technique with the uniform doping of 1 × 1015 cm−3 with integrated pocket SiGe layer for biosensing application. The p + and n
+ source and drain created by inducing the optimized work function which sense the neutral and charge biomolecules by
introducing the dimensional cavity. The paper also investigates the effect of the length and thickness variation on the cavity to
its drain current characteristics. In biomedical field, this research contributing a major analysis for sensing different charged
biomolecules.
Keywords Dual modulated charge plasma based SiGe vertical TFET . MOS-FET . Band-2-band tunneling (B2BT) . Subthreshold
swing or subthreshold slope (SS) . Low power (LP) . Biomolecule sensor . Sensitivity . Change and neutral biomolecules
1 Introduction techniques like introducing dual gate material, heterojunction
structure at the tunneling junction, optimizing work function
With the continuous shrinking in semiconductor device will and many more [6–8]. These techniques also useful to miti-
leads to various short channel effects in the nanoscale device. gate the ambipolar conduction which will count as a drawback
In the era of nanoscale device, there has various device pro- to the structure [9–11]. Another issue with TFET manufacture
posed to find the substitute in terms of low subthreshold slope is the high cost of ion implantation and the huge thermal
(SS) which is less than 60 mV/decade [1–3]. Among which, budget required for the high temperature thermal annealing
TFET is found to be an admirable device in terms of low procedure [12, 13]. As TFET is based on the working princi-
subthreshold slope with low OFF current [4, 5]. Due to its ple of Band to band tunneling (BTBT) and having the p-i-n
low off current, the total current ration of Ion/Ioff will overall structure as abrupt junction [14]. The P-i-n structure is heavily
increases. However, the TFET device is having the low on doped device and suffers with the issues like Random dopant
current, which can be removed by the utilizing various fluctuation (RDFs), which increase the manufacturing cost
along with leakage current in the device due to wide variation
in the sub-threshold voltage [15]. In order to make the abrupt
* Shailendra Singh junctions, diffusion process takes place for source and drain
shailendras.psit@gmail.com region, which is itself a difficult endeavor. All above short
comings are overcome by introducing the doping less tech-
1
ECE, PSIT Kanpur, Kanpur – Agra – Delhi, NH2, Bhauti, niques [16–18]. The doping less techniques further divided
Kanpur, Uttar Pradesh 209305, India into two parts: (1) charge plasma techniques and electrostatic
2
Department of Electronics Engineering, REC Kannauj, Aher, Uttar doped technique. Both of these techniques used different work
Pradesh 209732, India function in order to create different junction of the device. For
3
ECE, NIT Sikkim, Barfung Block, Ravangla, Sikkim 737139, India charge plasma technique, one has to presume that siliconSilicon
VT Þ biomolecules like bio-streptavidin and DNA [29]. This can
substrate will be kept within the Debye length ððεsi qþ6
1=2 be done by creating replica situation by considering the insu-
0:N Þ in order to follow the proper functioning of the device
lation value similar to the dielectric constant of the biomole-
[19]. In this equation, N are the carrier concentration of the
cules in the simulation work. However, the FET is restricted
silicon substrate, thermal voltage, its dielectric constant and
with the subthreshold value to 60 mV/decade with many short
silicon electronic charge respectively. Many of the techniques
channel effects. This reduce the device performance as the
involve for upgrading the feasibility of the device in terms of
basing voltage cannot be scaled further. In order to overcome
ION current and suppressing the ambipolar conduction [20,
these issues many literature and research analysis has been
21]. Among which dual gate is well integrating the doping
done to come with the solution, to mitigate these
less device for the formation of different junctions and for
shortcomings.
mitigating the ambipolarity in the reverse gate biasing. In the
The device scaling will lead to the short channel effect,
dual material, two different gate electrodes (1) auxiliary gate
which result in degradation of the device performance.
work function M1 (2) tunneling gate work function in which
Whenever, the channel length of the devices reaches below
auxiliary gate is higher than the tunneling gate [22]. Pollution
the 20 nm, the device fabrication become more complex [30].
monitoring and biological pathogen surveillance for early de-
As a result, a junctionless transistor (JLT) composed of
tection and diagnosis of systems has recently become a major
strongly doped silicon nanowires was proposed, as these tran-
concern [23, 24]. In this paper we consider the proposed de-
sistors do not require the development of any junctions.
vice for the application of the biosensor to detect the label free
Although the electrical properties of a junctionless
electrical biomolecules like DNA and protein cell. The first
field-effect transistor (JLFET) are more acceptable, random
biosensor was developed by the Befgveld [25] which were
dopant fluctuation (RDF) causes considerable inconsistency,
based on ion sensitive FET (ISFET). However, ISFET found
which is a serious issue when scaled to nanoscale dimensions.
to be good sensitive for charge biomolecules rather than the
As a result, charge-plasma-based FETs with no doping were
neutral biomolecules. This system is also incorporate with the
developed.
CMOS devices. To overcome these aforementioned short-
Using benefits of both dielectric and non-dielectric mate-
comings, Dual Metal-FET is introduced, however, this device
rials, TFET-based biosensors have been used to modulate,
comes with the drawback of the scaling issue which results in
leads to the development of DM-TFET biosensors. Tunnel
the variation of effective gate capacitance and hence
FETs based on charge plasma are made by deciding on the
high-power consumption takes place due to change in param-
right metalworking function to create a p + source, use a
eter, large detection time with poor sensitivity [26]. As charge
source/drain (S/D) electrode. The total define is n + drain area
plasma based Dual Metal TFET become a capable device to
in intrinsic silicon body (ni = 1015 cubic meters). As there are
detect the label free molecules with improve merits in terms of
no abrupt junctions in the arises in between source/channel
providing better sensitivity, response time and better profi-
and drain regions, so no RDF (random dopant fluctuation
ciency than the FET based biosensors. Dual metal incorporat-
arises, which will decrease the overall cost. As the manufac-
ed the suppression of ambipolarity of the device with enhance
turer need not to follow the high thermal process for diffusion
ON current.
and ion-implantation. For all mention, will finally come to a
A biosensor with long durability and feasible for detection
conclusion part of simplifying the fabrication process of
of disease and investigation of biohazards chemical in ecosys-
charge plasma over the conventional TFET.
tem. Because of its mass production and durability, the
In this draft, to optimize the device ON current, we have
nano-FET is highly efficient for the research purpose. In this
opted method for dual material metal gate work function. In
phenomenon, the nanogaps filled with the neutral or charged
which the tunneling gate are kept to be greater than auxiliary
biomolecules, which in corresponds varies the oxide capaci-
gate. Because of the disparity in gate work functions, the volt-
tance resulting in the change in drain current and threshold
age at the junction of M1 and M2 is abrupt, which results
voltage. Many of the protein have identical value of dielectric
boosting the drain current and transconductance of the device
constants like biotin streptavidin (k = 2.1), gluten, zein, ker-
along with the reduction in the drain induced barrier lowering.
atin (k = 5–10), charged amino acids (Glu, Lys, Arg and Asp
Short channel effects are reduced when dual material gate
(k = 11–26) [27, 28]. This biosensing can be perform by the
architecture is used without sacrificing any other device char-
etching out limited part of gate dielectric material by filling the
acteristic. However, there are a few drawbacks to using dielec-
nanogap. Due to this, when biomolecules immobilized in
tric modulated field-effect transistors (DM-FETs) in sensor
nanogap, will causes changes to the dielectric constant of the
that employ capacitance fluctuation signals. But
filling gaps and finally the drain current of the devices varies
Charge-plasma-based DM-VTFET for gate underlap regions
accordingly. The presence and absence of the biomolecules
for biosensor, resolves the issues mentioned above.
will cause changes in the electrical parameters which is then
The structure of Dual-material gate dielectric based on
used for measuring the sensitivity of neutral and charge
charged plasma. A gate underlap is included in a modulatedSilicon
VTFET (cavity). It is designed to immobilize biomolecules. work-function metal with 0.55 nm SiO2 oxide region for in-
This paper is focused for the commercial application as a low creasing charge plasma TFET electrostatic properties [26]. It
budget and cost-effective production at user’s end to sensor is done due to avoiding the effect of lattice mismatching of the
the biomolecules for medical perspective. device body i.e., is made up of silicon with SiO2 as a gate
oxide material. Intake work function for operating the device
is 4.5 eV. Also, with the SiGe pocket in between the
2 Device Structure and Simulation Framework source-channel tunneling junction with the square width of
2 nm each.
Figure 1(a) reflects the equivalent diagram of charge plasma In the charge-plasma-based device, the virtual source
based SiGe heterojunction Vertical TFET structure. Figure 1 and virtual drain region are created by attaching suitable
(b) Simulated contour diagram of the proposed device via work functions to gate electrodes VTFET. Platinum metal
silvaco TCAD tool. For employing parameter of intrinsic car- electrode work function 5.93 eV is used to create the “p+”
rier concentration with the value of ni = 1.0 × 1015 cm−3 with type source in the intrinsic silicon semiconductor.
non-metallurgical junctions. The device thickness is of 10 nm Similarly, the hafnium work function 3.90 eV is used to
while the channel length is 50 nm. This device is opted the create the “n+” type for the drain region in the device. In
gate stacking method with the specification 3 nm as a high-K all above drafting of the proposed device one thing need
(HfO2) material with 0.55 nm as (SiO2) material. Based on the to be acknowledge that the device thickness must be be-
findings, researchers looked into a comparison of low low the Debye length as express by the given Eq. (1) [19].
Fig. 1 (a) Schematic diagram (b) (a)
Simulated Contour diagram of
Dual Modulated Charge plasma
Source(ϕ = 5.93 eV)
based SiGe Vertical TFET for t SiO 2 =0.5
biomolecules sensing
My oxide SiGe My Oxide Biomolecule Cavity
Biomolecule Cavity
1 × 1015 cm−3
HfO2
HfO2
Channel
SiO2
My oxide
Silicon
Conductor
HfO2
t HfO 2 = 3 SiGe
Drain (φd= 3.90 eV)
(b)Silicon
1=2 simulation results, silvaco TCAD simulation software is used
ðεsi V T Þ to carry for the validation off proposed device. The model
þ 60:N ð1Þ
q used for simulating the device are Lombardi model,
Shockley Read Hall (SRH) model for re-combination purpose
Where, VT represent the thermal voltage, εsi represent the with Fermi -Dirac statistics with non-local band to band
dielectric constant, q and N terms represents the electronic tunneling [31, 32]. The generation rate at the tunneling junc-
charge carrier and Silicon carrier concentration of the tion is also calculated using the nonlocal band-2-band tunnel-
device. ing (BTBT) model. The device basically senses the biomole-
The energy bandgap, electron affinity and permittivity of cule by analyzing the variation of dielectric constant (K > 1)
SiGe material can be intended using following Eqs. (2 and 3). with reference to the air dielectric constant (K > 1). Whenever
the biomolecules come in contact with the cavity, the gate
1:17−0:47x þ 0:24x2 x < 0:85
E SiGe ¼ ð2Þ capacitance increases, resulting in an increase in the drive
5:88−9:58x þ 4:43x2 x > 0:85
current of the vertical TFET based on charge plasma tech-
εSiGe ¼ 11:9ð1 þ 0:35xÞ ð3Þ nique, making it suitable for biomolecule sensing.
Calibration Fig. 2 shows the calibration of doping less
Where, x is the mole fraction representing the variation from 0
to 1 in Si1-xGex. Schematic diagram of charge plasma based Vertical TFET simulation using the testified work at Vds
1.0 V. The data were extracted and plotted using the plot
SiGe vertical TFFT are identical to those for a conventional
digitizer program.
device, with the exception that a cavity region is formed to
detect the biomolecule immobilization. Here, the channel is
separated into two regions, which are denoted by the label’s
region1 and region 2. The first region is basically the entrance
space of the biomolecule called as cavity also as gate under lap
3 Results and Discussion
region (region 1), whereas the gate overlap region is known to
In the natural environment we have basically two types neutral
be region 2. Where, Lg represent the second region (region 2)
and charged biomolecules. For the assessment of the drain
as a gate overlap region with the dimension of 43 and 40 nm.
current characteristics different approach need to be taken
Lcavity is gate under cavity length, with values of 6 nm and
for the neutral and changes biomolecules. As in the neutral
10 nm, and values of 3.9 eV and 4.5 eV for dual-metal gate
biomolecules, we have to only focused and examine the di-
workfunctions ϕm1 and ϕm2, respectively. Various device de-
electric constant; however, in the case of the charged biomol-
sign parameters of the device are mentioned in Table 1.
ecules, both the dielectric constant and charge have to be
Finally, tcavity describes the cavity thickness and taken to
examined for drain current variation. As a result, when the
be 2/5 as height is to width ratio, which is also the gate
neutral biomolecules are taken in to the account for the pro-
underlap. The spacer thickness is fixed at 3.0 nm and
posed device of the Charge plasma based SiGe Vertical TFET
15.0 nm, respectively. The gate oxide thickness, tox, is gate
in the underlap region for simulating the drain current charac-
stacked with the HfO2 and SiO2 with the thickness of 0.5–
teristics. On the other hand, charged biomolecules for the
3 nm. When the Si substrate is unmasked and exposed to the
air, the SiO2 layer acts as an adhesive, binding the biomole- 10-5
cules together. The cavity region is attached with the biomol- 10-6
ecules which further act as a biosensor region. For typical 10-7
Drain Current Ids (A/Pm)
10-8
10-9
Table 1 Device specification of charge plasma based SiGe vertical 10-10
TFET 10-11
10-12
Parameters Values specified
10-13
10-14
Cavity dimension (Cavity thickness) From 6 to 10 nm
10-15 Conventional V-TFET[32]
Cavity height (Cavity width) From 2.5 to 5.5 nm
10-16 Vertical TFET (Simulation Work)
Applied Gate work function (ϕm1 and ϕm2) 3.9 eV and 4.5 eV
10-17
Gate stacked high k oxide thickness (HfO2) 3 nm
10-18
SiO2 gate oxide thickness 0.5 nm 0.00 0.25 0.50 0.75 1.00 1.25 1.50
Channel length 50 nm Gate voltage Vgs (V)
Charge plasma doping 1×1015 cm−3 Fig. 2 Calibration of doping less Vertical TFET simulation using the
Source/Drain length 30 nm reported work at Vds 1.0 V and Vgs 1.5 V. The data were extracted
and plotted using the plot digitizer programSilicon
underlap region will account the dielectric as well as changed (a) 10-7
biomolecules.
10-8 Cavity length = 6nm
Vgs =1.5 V , Vds = 0.5 V
3.1 Effects of Biomolecules Charge and Dielectric 10-9
Constant on Drain Current
Drain Current (A/µm)
10-10
10-11
In this section, we will analysis neutral biomolecules effect on
the drain current with the cavity length of 6 nm underlap 10-12 k=1
condition at Vds = 0.5 V and Vgs = 1.5 V shown by the -13 k=2
10
Figs. 3(a) and 5(a) respectively. However, the Figs. 4(a) and k=5
10-14 k=7
6(a) represent the division in the (Ids) drain drive current char-
k=9
acteristics owing to the cavity length of the 10 nm at the Vds = 10-15
k=11
1.5 V and Vgs = 1.5 V respectively. 10-16
With the creation of cavities, the barrier width between the
10-17
channel’s conduction band and the source’s valence band 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
widens, resulting in an extremely low likelihood of electron
Gate Voltage (V)
tunneling. As a result, current conduction is poor in this sce- (b)
nario. The device ON current grows with an increase in the
10-7 Cavity length = 6nm
underlap condition of the dielectric constant, as shown in Figs.
10-8 Vgs =1.5 V , Vds = 0.5 V
3(a), 4(a), 5(a) and 6(a) respectively.
On the other hand, the OFF-current remains nearly steady Drain Current (A/µm) 10-9
when the dielectric constant rises, resulting in increased band 10-10
bending and width reduction. The electrical characteristics 10-11
drain current for the scenario where charged biomolecules Nf = 0
10-12
are immobilized in the cavity region are shown in Figs. 3(a) Nf = 1e7
-13
and (b), 4(a) and (b), 5(a) and (b) and 6(a) and (b) respectively. 10
Nf = 1e9
When there are positively charged proteins, the ION current 10-14
Nf = 1e11
rises, and when there are negatively charged biomolecules in 10-15 Nf = 1e12
the cavity, the IOFF current decreases. It happens due to im- 10-16
mobilization of different polarity charge in the cavity region
10-17
reduces the barrier width between the channel’s conduction 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
band and the source’s valance band. Gate Voltage (V)
The cavity is occupied with the biomolecules with the val- (c)
ue of dielectric constant at K > 50, the model is found to be 10-7
ineffective. The dielectric constants of a few biomolecules are 10-8
Cavity length = 6nm
shown in Table 2. The conductivity of these biomolecules Vgs =1.5 V , Vds = 0.5 V
-9
10
must range initially from semi-conductor to insulator.
Drain Current (A/µm)
10-10
In this study, a gate underlaps dielectric modulated VTFET
10-11
has been constructed to incorporate the dielectric modulation
10-12
(DM) technology for label-free electronic detection based on
10-13
biomolecules such as aminopropyl triethoxysilane, Biotin, Nf = 0
10-14
protein, uricase, DNA, enzyme, and so on as sown in Nf = -1e7
Table 2 with their different values [33–35]. For the change 10-15 Nf = -1e9
10-16 Nf = -1e11
plasma based SiGe VTFET, we examined a gate underlap
Nf = -1e12
arrangement with the trap condition of the biomolecules. 10-17
This paper basically deals with Charge plasma based SiGe 10-18
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Vertical TFET in order to account the dielectric modulation
Gate Voltage (V)
technique for detection of label free biomolecules like
aminopropyl triethoxysilane, Biotin, protein, uricase, DNA, Fig. 3 Drain current variation under the condition of gate underlap (Cavity)
with the fixed dimension of 6 nm width with the height of 5.5 nm at Vds
enzyme etc. For this proposed device, we will analysis the
0.5 V and Vgs 1.5 V for (a) Different dielectric constant values (K = 1, 2,
underlap distribution of my oxide, in which basically the ox- 5, 7, 9, 11) (b) for the positive charge density biomolecules with the
ide region is uncovered because of interaction of the biomol- variation from Nf = 0 to 1e12. (c) for the negative charge density
ecules with the given cavity. biomolecules with the variation from Nf = 0 to -1e12Silicon
(a) Fig. 4 Drain current variation under the condition of gate underlap
-10 (Cavity) with the fixed dimension of 10 nm width with the height of
10 Cavity length = 10 nm
5.5 nm at Vds 0.5 V and Vgs 1.5 V for (a) Different dielectric constant
Vgs =1.5 V , Vds = 0.5 V
10-11 values (K = 1, 2, 5, 7, 9, 11) (b) for the positive charge density
biomolecules with the variation from Nf = 0 to 1e12. (c) for the
Drain Current (A/µm)
10-12 negative charge density biomolecules with the variation from Nf = 0 to
-1e12
10-13
10-14
k=1
10-15 −1 × 1012 cm2. When the cavity is filled with positively
k=2
k=5
charged biomolecules, the ON-current increases; however,
10-16
k=7 when neutral biomolecules filled the cavity, the OFF-current
10-17 k=9 remains nearly constant (dielectric constant K = 6).
k=11 With the condition shown in Figs. 3(c), 4(c), 5(c) and 6(c),
10-18
the device based on underlap charge plasma condition of SiGe
10-19
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Vertical TFET exhibit conflicting behavior for drain current as
Gate Voltage (V)
negative charge density increases, resulting in drain current
(b) deterioration. Figures 3 and 5 show that when the cavity
10-8 length is 6 nm, the drain current reaches its greatest value,
10-9 Cavity length = 10 nm whereas at Figs. 4 and 6 when the cavity length is 10 nm,
Vgs =1.5 V , Vds = 0.5 V the drain current reaches its minimum value.
10-10
Drain Current (A/µm)
10-11
3.2 Effects of Geometrical Parameter Variation on
10-12 Device Performance
10-13
3.2.1 Variation in Cavity Length Has an Effect on Drain
10-14 Nf = 0 Current
10-15 Nf = 1e7
Nf = 1e9 Now Figs. 7(a) and 7(b) shows the drain current fluctuation
10-16
Nf = 1e11 with respect to the cavity length (Lcavity). The ON current
10-17
Nf = 1e12 will be decreases as the cavity length will start increases from
10-18 6 to 10 nm keeping the gate width fixed with 50 nm. When
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
compared to drain current at Vds = 0:5 V, the foregoing
Gate Voltage (V) characteristics reveal that variance in drain current at Vds =
(c)
1E-9 1.5 V is insignificant. The fact that charge plasma based SiGe
Cavity length = 10 nm Vertical TFET exhibit tunnelling principle, whereas conven-
1E-10
Vgs =1.5 V , Vds = 0.5 V tional DM JLTFETs do not, explains the small fluctuation in
1E-11 drain current seen as a result of changing cavity length. The
Drain Current (A/µm)
1E-12 diffusion principle is followed by FET.
1E-13
3.2.2 Variation in Cavity Thickness Has an Effect on Drain
1E-14
Current
1E-15 Nf = 0
1E-16
Nf = -1e7 Figures 8(a), 8(b) demonstrates the drain current versus gate
Nf = -1e9 bias for various cavity thickness (tcavity) values while keep-
1E-17
Nf = -1e11 ing channel length at 50 nm. When Vds = 1.5 V is compared
1E-18 Nf = -1e12 to Vds = 0.5 V, a slight change in drain current is noted. With
1E-19
the variation in tcavity (cavity thickness) grows from 2.5 to
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 5.5 nm, the variance in drain current with relation to Vgs
Gate Voltage (V) (gate-source) voltage decreases. Figure 8 demonstrates that
when the cavity thickness tcavity is 2.5 nm, the drain current
reaches its extreme value. The effect of changing the tcavity
As demonstrated in Figs. 3 and 4, a remarkable fluctuation on the Ids vs Vgs features is seen in Fig. 8. Higher tunnelling
in the drain current is achieved during Nf = 1 × 1012 cm2 to barriers at source-channel interface due to introduce SiGeSilicon
(a) Fig. 5 Drain current variation under the condition of gate underlap
10-5 (Cavity) with the fixed dimension of 6 nm width with the height of
Cavity length = 6 nm 5.5 nm at Vds 1.5 V and Vgs 1.5 V for (a) Different dielectric constant
10-6 Vgs =1.5 V , Vds = 0.5 V values (K = 1, 2, 5, 7, 9, 11) (b) for the positive charge density
10-7 biomolecules with the variation from Nf = 0 to 1e12. (c) for the
negative charge density biomolecules with the variation from Nf = 0 to
Drain Current (A/µm)
10-8
10-9
-1e12
10-10
10-11
10-12 k=1
3.3 Variation in the DCS (Drain Current Sensitivity)
10-13
k=2 with Various Parameters
10-14 k=5
k=7 The drain current sensitivity of biosensors can be used to
10-15
k=9 assess their performance: The drain current levels while the
10-16 k = 11
cavity is empty and filled with a dielectric material are repre-
10-17
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 sented by the Drain Current Sensitivity factor ID and IbioD,
Gate Voltage (V) represent by Eq. (4) respectively. By variation of the different
(b) values of neutral biomolecules and dielectric constant with
10-6 charge density of biomolecules.
Cavity length = 6 nm
10-7
Vgs =1.5 V , Vds = 1.5 V
10-8
ðI d −I Biod Þ
10-9 DCS ð%Þ ¼ ð4Þ
Drain Current (A/µm)
*100
Id
10-10
10-11 Figure 9(a) and 9(b) reflect the drain current sensitivity in
10-12 terms of gate voltage variation for two cavity length of the
10-13 underlap region with 6 nm and 10 nm respectively.
Nf = 0
10-14 Nf = 1e7 Figure 10 (a) and (b) demonstrates drain current sensitivity
10-15 Nf = 1e9 characteristics for Vds = 1.5 V at 6 nm cavity length and
10-16 Nf = 1e11 10 nm cavity length for various dielectric constant for neutral
10-17 Nf = 1e12 biomolecules with different charge densities. The biomole-
10-18 cules are trapped in the cavity when the dielectric constant
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 of the cavity areas is gradually increased form air to the en-
Gate Voltage (V) hanced values i.e., K > 1. Form the figure it can be depicted
(c) that drain current sensitivity is proportionate with the value of
10-6
10-7 Cavity length = 6 nm dielectric constant value. As can be predicted form the Fig. 9
-8
Vgs =1.5 V , Vds = 1.5 V (b) and 10(b) that, drain current sensitivity increases with the
10
increase with the positive concentration of biomolecules. It
10-9
Drain Current (A/µm)
also causes shift in the drain current and potential to show
10-10
the effect of the drain current sensitivity of charge plasma
10-11
based SiGe Heterojunction Vertical TFET as a proportionate
10-12 behavior to the predict the presence of biomolecules in the
10-13 cavity. Table 3 shows that the factor of Drain current sensitiv-
Nf = 0
10-14 ity (DCS) that grows as propionate the channel width in-
Nf = -1e7
10-15 Nf = -1e9 creases However, long channel length devices have poor sens-
10-16 Nf = -1e11 ing capability. For different dielectric constant value and
10-17 Nf = -1e12 charge density levels, it is clear that a low gate bias results in
10-18
a large improvement in drain current sensitivity.
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Gate Voltage (V)
3.3.1 Variation in Cavity Length Has an Effect on Drain
Current Sensitivity (DCS)
pocket layer which reduce the tunneling barrier for high
values of Vgs, which finally resulting in a drop in drain current Now in Fig. 11(a) and 11(b) DCS varies with respect to the
as tcavity grows. drain-source voltage Vds = 0.5 and 1.5 V. However, theSilicon
(a) Table 2 Biomolecule equivalent value to dielectric Constant
10-7
10-8 Cavity length = 10 nm Name of biomolecule Equivalent K value
Vgs =1.5 V , Vds = 1.5 V
10-9
Aminopropyl triethoxy-silane 3.570
10-10
Drain Current (A/µm)
Biotin 2.630
10-11 Protein 2.500
10-12 Uricase 1.540
10-13
k=1
10-14
k=2
10-15 k=5 reader can see the small fluctuation in drain current sensitivity
10-16
k=7
k=9 when Lcavity changes. As can be analyses from the Fig. 11,
10-17 k = 11 the DCS variation will increases with respect to gate source
10-18 voltage. At the 10 nm cavity length the sensitivity reflects its
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
maximum value. In the fraction where cavity length is not
Gate Voltage (V)
much affected to the drain current sensitivity due to the fact
(b) 10 -7
Cavity length = 10 nm
10-8
Vgs =1.5 V , Vds = 1.5 V (a)
10-9 10-9
10-10 10-10 Vgs =0.5 V , Vds = 1.5 V
Drain Current (A/µm)
10-11 Drain Current (A/µm) 10-11
-12
10
10-12
-13
10
10-13
10-14 Nf = 0
Nf = 1e7 10-14
10-15
Nf = 1e9
10-16 10-15
Nf = 1e11
Lcavity = 6
10-17 Nf = 1e12 10-16
Lcavity = 7
10-18 10-17 Lcavity = 8
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Lcavity = 9
Gate Voltage (V) 10-18
Lcavity = 10
(c) 10 -7
10-19
Cavity length = 10 nm 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
10-8 Vgs =1.5 V , Vds = 1.5 V Gate Voltage (V)
(b)
10-9 10-7
Drain Current (A/µ m)
-10
10 10-8 Vgs =1.5 V , Vds = 1.5 V
-11
10 10-9
10-12
10-10
Drain Current (A/µm)
10-13
10-11
Nf = 0
10-14
Nf = -1e7 10-12
10-15
Nf = -1e9 10-13
10-16 Nf = -1e11
10-14 Lcavity = 6 nm
10-17 Nf = -1e12
10-15 Lcavity = 7 nm
10-18
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Lcavity = 8 nm
10-16 Lcavity = 9 nm
Gate Voltage (V)
10-17 Lcavity = 10 nm
Fig. 6 Drain current variation under the condition of gate underlap
(Cavity) with the fixed dimension of 10 nm width with the height of 10-18
5.5 nm at Vds 1.5 V and Vgs 1.5 V for (a) Different dielectric constant 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
values (K = 1, 2, 5, 7, 9, 11) (b) for the positive charge density Gate Voltage (V)
biomolecules with the variation from Nf = 0 to 1e12. (c) for the
Fig. 7 Variation of drain current characteristics with respect to the cavity
negative charge density biomolecules with the variation from Nf = 0 to
length variation form the 6 nm to 10 nm for the gate source voltage Vgs
-1e12
= 1.5 V (a) Vds = 0.5 V and (b) Vds = 1.5 VSilicon
(a) (a)
10-9 104
Vgs =0.5 V , Vds = 1.5 V K=2 Cavity length = 6nm
10-10 Vgs =1.5 V , Vds = 0.5 V
K=5
10-11 K=7
Drain Current Senstivity
10-12 K=9
Drain Current (A/µm)
103 K=11
10-13
10-14
10-15
10-16
102
10 -17 tcavity = 2.5 nm
tcavity = 3.5 nm
10-18
tcavity = 4.5 nm
10-19 tcavity = 5.5 nm
10-20 101
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Gate Voltage (V) Gate Voltage (V)
(b) (b)
104
10 -7 Cavity length = 6nm
Vgs =1.5 V , Vds = 1.5 V
10 -8 Vgs =1.5 V , Vds = 0.5 V
10-9
10-10
Drain Current Sensitivity 103
Drain Current (A/µm)
10-11
10-12
10-13 102
-14
10
10-15 Nf = 1e7
10-16 Nf = 1e9
tcavity = 2.5 nm 101
10-17 tcavity = 3.5 nm Nf = 1e11
10-18 tcavity = 4.5 nm Nf = 1e12
10-19 tcavity = 5.5 nm
100
10-20
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
GateVoltage (V)
Gate Voltage (V)
Fig. 9 Drain current sensitivity variation of Charge plasma based SiGe
Fig. 8 Variation of drain current characteristics with respect to the cavity
Vertical TFET with respect to the cavity gate voltage (V) fixed at 6 nm
thickness variation form the 2.5 nm to 5.5 nm for the gate source voltage
width with the height of 5.5 nm at Vds 0.5 V and Vgs 1.5 V for (a)
Vgs = 1.5 V (a) Vds = 0.5 V and (b) Vds = 1.5 V
Different dielectric constant values (K = 1, 2, 5, 7, 9, 11) (b) for the
positive charge density biomolecules with the variation from Nf = 0 to
1e12
that charge plasma-based Pocket SiGe Vertical TFET is basi-
cally using the tunneling mechanism, however in the case of
the conventional FET, diffusion process is used for the chan- voltage decreases. In the case of the cavity thickness at
nel transmission. As can be seen from Table 4, variation of 2.5 nm, the drain current sensitivity shows the maximum
drain current sensitivity with respect to cavity length variation value, however in the case of 5.5 nm cavity thickness in
is recorded. The DCS value is raises with the cavity length and DCS shows the minimum values. The drain current sen-
shown to be maximum at Lcavity = 10 nm. sitivity diminishes as the cavity length (tcavity) in-
creases, which is due to an increase in the tunneling
3.3.2 The Influence of Cavity Thickness (Tcavity) on DCS barrier at the source-channel boundary, resulting in the
less sensing of the proposed device charge plasma based
Figure 12(a) and 12(b) demonstrate the drain current sensitiv- SiGe heterojunction Vertical TFET. As can be seen from
ity variation (DCS) as a function of cavity thickness tcavity for Table 5, variation of drain current sensitivity with respect
Vds 0.5 V and 1.5 V respectively. It shows that, when the to cavity thickness variation is recorded. The DCS value
tcavity (cavity thickness) grows from 2.50 nm to is raises with the cavity thickness and shown to be max-
5.50 nm, the DCS voltage with respect to the gate imum at tcavity = 5.5 nm.Silicon
Table 3 Variations of drain
current sensitivity with respect to Dielectric constant DCS (Drain Current Sensitivity)
dielectric constant and positive
biomolecules Vds=0.5 V Vds=1.5 V
Cavity (6 nm) Cavity (10 nm) Cavity (6 nm) Cavity (10 nm)
K=2 80.46586 119.9166 112.06047 163.46123
K=5 529.33125 888.17709 368.39524 600.43308
K=7 1419.89688 2132.34902 1295.99963 1349.28134
K=9 3274.52697 4673.52129 4692.57192 2943.90593
K=11 7645.38766 9685.62485 10,723.00076 6259.3497
4 Conclusion
(a) In this paper, we have basically analysis the charged
104 Cavity length = 10 nm and neutral biomolecule detection with the proposed de-
Vgs =1.5 V , Vds = 0.5 V vice of charge plasma based SiGe heterojunction
Vertical TFET for under lap region. This draft makes
Drain Current Sensitivity
103 its own space to the readers by distinguishes it from
other sensing devices currently on the commercial ap-
plication for showing its maximum sensitivity in detec-
102 tion of the charge and neutral biomolecules. So, the
proposed device reflects its improved performance for
cost-effective construction of biomedical diagnosis in-
101 Nf = 1e12 struments, as it achieves increased sensitivity by a mod-
Nf = 1e11 erate optimum selection to the geometrical parameters
Nf = 1e9 like cavity length and its thickness at the tunneling
100 Nf = 1e7 junction interface with suitable biasing condition. The
0.2 0.4 0.6 0.8 1.0 1.2 1.4 biasing voltage Vgs is kept ot be 1.5 V, while the
Gate Voltage (V) Vds is varied from 0.5 to 1.5 V. Finally, form the
(b) proposed device of charge plasma based SiGe vertical
104 TFET it can be concluded that, it is a low leakage
Cavity length = 10 nm device current and highly sensitive factor for the change
Vgs =1.5 V , Vds = 0.5 V
and neutral biomolecules, after analyzing its variation to
Drain Current Sensitivity
103 different cavity dimension parameters with dielectric
constant to its electrical characteristics.
102
K=2
K=5 Table 4 Variations of drain current sensitivity (DCS) with respect to
1
10 K=7 cavity length variation
K=9
Lcavity (nm) Maximum DCS (Drain Current Sensitivity)
K=11
100 At K=5
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Gate Voltage (V) Vds=0.5 V Vds=1.5 V
Fig. 10 Drain current sensitivity variation of Charge plasma based SiGe 7 112.060 1688.2
Vertical TFET with respect to the cavity gate voltage (V) fixed at 10 nm
8 368.395 496.09
width with the height of 5.5 nm at Vds 0.5 V and Vgs 1.5 V for (a)
Different dielectric constant values (K = 1, 2, 5, 7, 9, 11) (b) for the 9 1295.996 197.74
positive charge density biomolecules with the variation from Nf = 0 to 10 10,723.0 39.68
1e12Silicon
(a) (a)
Vgs =1.5 V , Vds = 0.5 V tcavity = 2.5 nm Cavity length = 6 nm
104 tcavity = 3.5 nm Vgs =1.5 V , Vds = 0.5 V
104
tcavity = 4.5 nm
Drain Current Sensitivity
Drain Current Sensitivity
tcavity = 5.5 nm
103
102 103
Lcavity = 6
Lcavity = 7
101 Lcavity = 8
Lcavity = 9
Lcavity = 10 102
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Gate Voltage (V) Gate Voltage (V)
(b) 5
(b)
10
Cavity length = 6nm
Vgs =1.5 V , Vds = 1.5 V 4 Vgs =1.5 V , Vds = 1.5 V
10
Drain Current Sensitivity
Drain Current Sensitivity
104
103
103
102
Lcavity = 7
102 Lcavity = 8 tcavity = 2.5 nm
Lcavity = 9 101 tcavity = 3.5 nm
Lcavity = 10 tcavity = 4.5 nm
tcavity = 5.5 nm
0.2 0.4 0.6 0.8 1.0 1.2 1.4 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Gate Voltage (V) Gate Voltage (V)
Fig. 11 Drain current sensitivity variation of Charge plasma based SiGe Fig. 12 Drain current sensitivity variation of Charge plasma based SiGe
Vertical TFET with different values of cavity length variation form 6 nm Vertical TFET with different values of cavity thickness variation form
to 10 nm at Vgs 1.5 V for (a) Vds = 0.5 V and (b) Vds = 1.5 V 2.5 nm to 5.5 nm at Vgs 1.5 V for (a) Vds = 0.5 V and (b) Vds = 1.5 V
Acknowledgements Not Applicable.
Funding Statement The author(s) received no financial support for the
research, authorship, and/or publication of this article.
Table 5 Variations of drain current sensitivity (DCS) with respect to
cavity thickness variation Availability of Data and Material Not applicable.
tcavity (nm) Maximum DCS (Drain Current Sensitivity) Author Contributions All authors have equally participated in the prepar-
ing of the manuscript during implementation of ideas, findings result, and
At K=5 writing of the manuscript.
Vds=0.5 V Vds=1.5 V
Data Availability Not applicable.
2.5 163.461 2772.2
3.5 600.433 857.394 Declarations All procedures performed in studies involving human
4.5 1349.281 218.56 participants were in accordance with the ethical standards.
5.5 2943.90 36.062
Consent to Participate Not applicable.Silicon
Consent for Publication The Author transfers his copyrights to the 18. Wadhwa G, Kamboj P, Raj B (2019) Design optimisation of
publisher. junctionless TFET biosensor for high sensitivity. Adv Nat Sci
Nanosci Nanotechnol 10(4):045001
Conflict of Interest The authors declare that there are no conflicts of 19. Bala S, Khosla M (2018) Design and analysis of electrostatic doped
interest. tunnel CNTFET for various process parameters variation.
Superlattice Microst 124:160–167
20. Gupta, Shilpi, Subodh Wairya, and Shailendra Singh (2021)
Analytical modeling and simulation of a triple metal vertical
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