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Journal of
Materials Chemistry C
Materials for optical, magnetic and electronic devices
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: C. Li, L. Pan, C.
Deng, T. Cong, P. Yin and Z. Wu, J. Mater. Chem. C, 2017, DOI: 10.1039/C7TC04166G.
Volume 4 Number 1 7 January 2016 Pages 1–224
Journal of
Materials Chemistry C
Materials for optical, magnetic and electronic devices
www.rsc.org/MaterialsC
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ISSN 2050-7526
PAPER~
Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
Please note that technical editing may introduce minor changes
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rsc.li/materials-c
Page 1 of 26
Journal of Materials Chemistry C
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DOI: 10.1039/C7TC04166G
network fabricated by electrophoretic method
Chengwei Lia, Lujun Pana,*, Chenghao Denga, Tianze Conga, Penghe Yinb, Zhenlin Wua
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a
School of Physics, Dalian University of Technology, No. 2 Linggong Road, Ganjingzi District, Dalian
116024, P.R. China
b
Key Laboratory for Micro/Nano Technology and Systems of Liaoning Province, Dalian University of
Technology, Dalian, 116024, P.R. China
Abstract
A highly sensitive, wide range pressure sensor based on carbon nanocoil (CNC)
network fabricated by electrophoretic method has been fabricated and studied. The
pressure sensor can withstand a maximum pressure of 100 kPa, and can maintain a
high sensitivity of more than 150/kPa when the pressure is more than 50 kPa. It is
worth noting that it has an ultrahigh sensitivity of 193/kPa at the pressure of 70 kPa. A
high stability and reproducibility of more than 10000 loading-unloading cycles, and a
fast response time of approximately 48 ms have been achieved. The pressure sensor
can clearly distinguish the minimum pressure of 0.5 kPa. This study presents a
concept of optimal value which can be used to evaluate the performances of different
types of pressure sensors. The optimal value of this sensor is up to 3.72×106, which is
300 times higher than most of the current pressure sensors. Practically, the pressure
sensor shows an excellent performance in detection of finger tapping, air pressure,
*
Corresponding author. E-mail: lpan@dlut.edu.cn
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Journal of Materials Chemistry C Accepted Manuscript
A highly sensitive, wide range pressure sensor based on carbon nanocoil
Journal of Materials Chemistry C
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DOI: 10.1039/C7TC04166G
devices and pressure detection equipment because of its ultrahigh sensitivity and
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pressure resistance.
1. Introduction
In recent years, with the fast increase of the demand for intelligent devices, flexible
pressure sensors have become one of the most widely used sensors and played
important roles in the area of pressure detection. The traditional pressure sensors are
focused on the mechanical devices, which indicates the pressure by the deformation
of the elastic element, but this kind of pressure sensors are normally large and heavy.
With the development of nanomaterials and nanotechnology, the pressure sensors
which use nanomaterials as the sensing medium have come into being with small size,
light weight and high accuracy. Especially with the help of micro-electromechanical
systems and nano-electromechanical systems, the research of nanomaterial-based
pressure sensors has focused on the device miniaturization, which brings the
advantages of low power consumption and high reliability.1 Significant efforts are
underway to develop pressure sensors that can be used in health monitor,2-7 electronic
skin,8-11 wearable devices,12-14 and microgravity detection.2, 15-18 Plenty of researches
on pressure sensors have been reported currently, and a large variety of nanomaterials
have been investigated. Lee et al. fabricated a kind of pressure sensor whose sensing
medium was woven composite fiber structure. The pressure sensor can detect a
maximum pressure of 20 kPa, but its sensitivity is 0.21/kPa.13 Park et al. have
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and vibration, exhibiting great potential in the applications of vibration detection
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mixture composed of carbon nanotubes (CNTs) and polydimethylsiloxane (PDMS)
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prepolymer into interlocked micro-dome arrays. Then, two composite films with
micro-dome arrays were combined with the patterned sides facing each other to form
a pressure sensor. It can detect a pressure of 59 kPa, and its sensitivity can reach
-15.1/kPa.9 Song et al. fabricated a pressure sensor using conformal graphene film as
the sensing medium. The film was deposited on a 3D grating micro-structured quartz
by a chemical vapor deposition (CVD) method. The sensor can detect from 0 to
40 kPa, and possesses a sensitivity of -6.524/kPa in a low-pressure range of 0-200 Pa.
However, its sensitivity was dropped to -0.0005/kPa when the pressure was higher
than 1 kPa.19 It has been reported by Wang et al. that a pressure sensor was fabricated
by two layers of SWCNTs/PDMS films with the patterned surfaces by silk mould
placed face-to-face. This kind of pressure sensor owns a maximum pressure of
1.2 kPa and a sensitivity of 1.8/kPa. It is worth noting that the pressure sensor can
distinguish some ultralight objects clearly, such as an ant.10 Pan et al. have
successfully fabricated a sensitive pressure sensor which is assembled by a kind of
elastic microstructured conducting polymer film, consists of inter-connected
hollow-sphere structures of polypyrrole. The pressure sensor has a high sensitivity of
133.1/kPa when the pressure is less than 0.03 kPa, but its sensitivity is less than 1/kPa
when the pressure is higher than 0.5 kPa, it limits the application of this pressure
sensor to some extent.17 Lipomi et al. reported a pressure-resistant sensor that uses
PDMS as the flexible substrate, and orthogonal CNT network as the sensing medium.
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successfully obtained the composite elastomer films which were fabricated by a liquid
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DOI: 10.1039/C7TC04166G
is 2.3×10-4/kPa.20
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In this paper, a highly sensitive, wide range pressure sensor based on carbon nanocoil
(CNC) network is proposed, on the basis of our previous research.21 Compared with
nanowires, CNCs have a unique three-dimensional helical structure, with coil
diameter, line diameter and coil pitch of 500-800 nm, 100-200 nm and 500-700 nm,
respectively. They also possess excellent mechanical and electrical properties, with
the elastic coefficient of 0.12 N/m, and the resistivity of 1×10-4 Ωm at room
temperature.22-28 Compared with nanowires, a larger strain can be applied due to the
spring-like structure of the CNCs. The three-dimensional helical structure of CNCs
determines that the CNCs mostly point contact with each other. This contributes to the
uniform disperse of CNCs in liquid, making it easier to form a network structure. The
micro-contact between adjacent CNCs are easier to change than nanowires during the
pressing process. In addition, the comb-shape patterned electrodes, where a plenty of
CNCs were deposited, have a large number of conductive pathways to ensure good
conductivity and stability. At the same time, the pressure sensor based on CNC
network shows excellent sensing properties, which shows great potential for future
applications in the pressure detection, vibration detection as well as MEMS and
NEMS devices.
2. Experimental
2.1. Synthesis of CNCs. The CNCs used in this experiment were synthesized as
4
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This pressure sensor can withstand an ultrahigh pressure of 1 MPa, but its sensitivity
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quartz substrate and dried. Then the substrate was calcined at 710˚C for 30 min in
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order to oxidize the catalysts. Carbon nanocoils were grown from the catalysts by a
thermal chemical vapor deposition system at 710˚C for 30 min by introducing
acetylene gas of 15 sccm and Ar gas of 325 sccm rate.29-33
2.2. Fabrication of the Pressure Sensor Based on the CNC Network. The base and
curing agent of PDMS (Dow Corning Sylgard 184) were mixed in 10:1 mass ratio.
After stirring evenly, the liquid PDMS was extracted with a syringe and dripped into a
square container to control the thickness of the PDMS to 1 mm. Then the square
container was evacuated in a vacuum oven for 30 min to remove the air bubbles in the
PDMS. After that, the container was dried in an oven at 60˚C for 30 min to form solid
PDMS. The solid PDMS was cut to a size of 4 cm × 1.5 cm. Then a titanium film with
a thickness of 10 nm and a gold film with a thickness of 100 nm were sequentially
sputtered on the PDMS substrate (Kert J. Lesker LAB18). After this, several pairs of
comb-shaped electrodes were fabricated on the substrate using a lithography method
(KARL SUSS MA6).
The electrophoresis method was used to fabricate the CNC network in this work.34
Both ends of the gold electrodes were applied with 5 V, 1 kHz alternating current by a
signal generator (Agilent 33120A), while about 50 µL of alcohol solution dispersed
with CNCs (0.4 mg/mL) was dripped between the gold electrodes. CNCs in the
alcohol can be concentrated in the middle of each pair of electrodes due to the
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follows. The Fe2 (SO4)3/SnCl2 solution used as catalyst precursor was dropped on the
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be gradually formed.
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The liquid PDMS with the thickness of 1 mm was prepared using the similar method.
The container was placed in a constant temperature oven and dried at 65˚C for 17 min
to obtain a viscous PDMS layer. It is then combined with the previously prepared
solid PDMS substrate which has the CNC network and cured in the oven at 60˚C for
30 min to form a CNC network based pressure sensor. The fabrication process of the
pressure sensor based on CNC network is shown in Figure 1.
2.3. Characterization of CNC Network and Sensing Properties Measurement of
the Pressure Sensor. Optical microscopy (PSM-1000) and scanning electron
microscopy (FEI NOVA NanoSEM 450) were used to observe the microstructure of
the CNC network. A universal material testing machine (YL-S70, Guangzhou
Aipeisen Instruments Co., Ltd) was used to apply pressure to the sensor during the
pressure test. A high precision source meter (Agilent B2902A) was used to measure
the relative change in the resistance as the sensor was pressed.
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electrophoresis effect. With the increase of electrophoresis time, the CNC network can
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Figure 1. The fabrication process of the pressure sensor based on CNC network.
3. Results and discussion
Figure 2 is the electrophoresis process of the CNC network between the comb-shaped
electrodes. Figure 2a-c show the distribution of the CNCs at different degrees of
electrophoresis under an optical microscope. It can be seen that the number of the
CNCs dispersed between each pair of the electrodes gradually increases with the
progress of the electrophoresis process. It is also observed that the CNC network is
more and more obvious with the increase in the number of the CNCs between each
pair of electrodes. Figure 2d shows the distribution of CNCs between several pairs of
the electrodes using SEM. The distribution of CNCs between one pair of the
electrodes is shown in Figure 2e, and a large number of CNCs between the electrodes
can be observed. Figure 2f is an enlarged view of the electrode position of Figure 2e,
showing that the number of CNCs connected to the electrode is relatively small. In
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connections between the CNCs and electrodes are mainly point contacts. The cross
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section image of the pressure sensor before encapsulation is shown in Figure 2g. It is
obvious that the CNCs between the electrodes are relatively thin, which are
intertwined with each other. The cross section image of the sensor after encapsulation
is shown in Figure S1, it is observed that the CNCs are basically in a single layer and
uniformly distributed, different from some pressure sensors consisting of porous
structures.35 Figure 2h shows the resistance change of the CNC network after 1 to 10
times of electrophoresis. It is observed that the resistance decreases exponentially
from 1410 to 59.6 Ω gradually during the 10 times of electrophoresis. It can be found
that the CNC network reached saturation state after the 6th electrophoresis as the
resistance has a total reduction of only 31.3 Ω from the 6th to the 10th. This is
consistent with the observation from Figure 2 that the CNC network is homogeneous
after each electrophoresis and the macro performance of the sensor is stable.
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addition, due to the three-dimensional helical structure and the rigidity of CNCs, the
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Figure 2. The electrophoresis process of the CNC network between the comb-shaped
electrodes. (a) - (c) The distribution of the CNCs between the comb-shaped electrodes
with the increase of the electrophoresis progress in the optical microscope. (d) The
SEM image of the distribution of the CNCs between several pairs of the comb-shaped
electrodes after electrophoresis. (e) The distribution of CNCs between one pair of the
electrodes. (f) The connection between the CNCs and electrode. (g) The cross section
image of the CNCs between one pair of the electrodes before encapsulation. (h) The
relationship between the resistance of the CNC network and the times of
electrophoresis.
Figure 3 shows the resistance change of the sensor as the pressure is applied. It can be
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DOI: 10.1039/C7TC04166G
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pressure from 0 to 100 kPa. The whole pressing process is divided into two stages
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(0-30 kPa and 30-100 kPa). Due to the fact that the connections between the adjacent
CNCs in the sensor are mostly point to point, during the pressing process in stage 1,
as the pressure is 0, this structure has a large number of contact points. Therefore, it
has many conductive paths when the pressure sensor is not pressed. When the sensor
is subjected to light pressure (0-30 kPa), due to the poisson ratio of the substrate, the
PDMS can be deformed, resulting in a decrease of contact points and eventually the
reduction of conductive pathways, as shown in Figure 3b. The sensing mechanism is
similar to the research by Hu et al.36
In stage 1, it is assumed that the conducance of the sensor under the pressure can be
expressed as,
G=
1
βN
R0
(1)
where G, N are the conductance of the pressure sensor and the number of the contact
points between the adjacent CNCs, respectively. β is a proportional constant.
The number of contact points are supposed to be decreased with pressure, whose rate
is related to the number of contact points, and can be expressed as,
dN
= −α N
dp
(2)
where α is a proportional constant. Therefore, the number of contact points can be
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seen from Figure 3a that R/R0 changes from 1 to 16435 with the increasing of the
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N = Ae −α p
(3)
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where A is a constant. Then, R0/R can be obtained from the Equation (1) and (3) as
follow,
R0
= Aβ e −α p
R
(4)
Therefore, the relationship between the logarithm of R/R0 and pressure can be
expressed as,
ln
R
= α p − ln Aβ
R0
where -lnAβ can be replaced by a new constant b, then,
ln
R
=α p +b
R0
(5)
A linear relationship between the logarithm of R/R0 and pressure is obtained, and this
is consistent with the fitting result in the inset of Figure 3a. According to the Equation
(5) and the fitting result, the constant α = 0.18 .
During the pressing process in the stage 2, the sensor is subjected to high pressure
(30-100 kPa). In this case, the resistance change not only comes from the decrease of
the contact points of the CNCs between the comb-shaped electrodes, but also comes
from the connection between the CNCs and the electrodes. Compared with the CNCs
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expressed as,
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area is much smaller, and some CNCs are in semi-contact with the electrodes. This
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makes the contact resistance between the CNCs and the electrodes easily affect the
total resistance of the sensor. Due to the rigidity of the CNCs, a slippage is caused
between the CNCs and electrodes when the sensor is subjected to a high pressure, and
as the pressure increases, the CNCs are gradually separated from the electrodes, as
shown in Figure 3b. As a result, the total resistance of the sensor will be greatly
changed, as shown in Figure 3a.
In stage 2, the number of contact points between CNCs and electrodes are supposed to
be decreased with pressure, whose rate is related to the number of contact points
between CNCs and electrodes, and the number of contact points among CNCs
between the electrodes, it can be expressed as,
dN
= −β ' NM
dp
(6)
M = N −α '
where M is the number of the contact points between the adjacent CNCs, N is the
number of the contact points between CNCs and electrodes, and α’, β’ are constants.
Therefore, the conductive pathways can be regarded as a M×N network, and the
schematic illustration of the network is shown in Figure S2.
The number of contact points between CNCs and electrodes decrease with the
increase of the pressure, so it is assumed that relative resistance change during the
pressing process can be expressed as,
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between the electrodes, the number of CNCs in contact with the electrodes per unit
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ω
(R/ R 0 )
(7)
where ω is a constant.
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It can be deduced from Equation (6) and (7) as follow,
d (R/ R 0 )
= dp
β 'ω − α ' β '(R/ R 0 )
(8)
Then,
β 'ω −α ' β '(R/ R0 ) = e−α 'β 'c e− A'α 'β ' p
(9)
where A’, c are constants.
Therefore, R/R0 can be deduced from Equation (9) as follow,
R / R0 = − fe−γ p + z
(10)
e−α ' β 'c
1
where f, γ, z are constants, and f =
, γ = A 'α ' β ' , z = ω .
α 'β '
α'
An exponential relationship between R/R0 and pressure is obtained, and this is
consistent with the fitting result in stage 2 of Figure 3a. According to the Equation (10)
and the fitting result, the constant γ =0.032 .
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N=
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The relationship between R/R0 and pressure. The inset is the linear relationship
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between the logarithm of R/R0 and pressure in stage 1. (b) The schematic of the sensor
resistance change under light pressure and high pressure.
Figure 4 shows the pressure properties of fabricated CNC network based pressure
sensor. Figure 4a shows the I-V characteristics of the pressure sensor under different
pressures from 0 to 100 kPa. It is found that the I-V curve is linear under different
pressures, implying a good Ohmic behavior, and with the increase of pressure, the
slope of the I-V curve gradually decreases and finally approaches 0. The inset in
Figure 4a shows the zoom-in I-V curves for the pressures from 40 to 100 kPa. Figure
4b shows the relationship between the sensitivity and the pressure in the pressing
process, and the sensitivity is defined as S =
(R− R0 ) / R0
. It is found that the
p
sensitivity of the pressure sensor rises rapidly from 0 to 182 /kPa with the pressure
increased from 0 to 50 kPa, and remains essentially unchanged as the pressure
increases from 50 to 100 kPa. It is noteworthy that the sensitivity reaches up to 193
/kPa at the pressure of 70 kPa, which is a high value for pressure sensors. After 10000
cycles of pressure test, the initial resistance remain unchanged, which is shown in
Figure 4c. It illustrates that this pressure sensor is very robust and reliable. Figure 4d
is the zoom-in data of Figure 4c showing 100 cycles of pressure and resistance
monitoring. To determine the response time, an instantaneous pressure is applied on
the pressure sensor. The real-time resistance change of the sensor versus time is
14
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Figure 3. The resistance change of the pressure sensor during the pressing process. (a)
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in about 48 ms, indicating that the response time should be less than 48 ms. Figure 4f
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shows a real-time resistance detection when a small pressure is applied to the sensor.
It illustrates that the pressure sensor can clearly distinguish the pressure of 0.5 kPa.
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shown in Figure 4e, from which it is obvious that the resistance change is completed
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I-V characteristics under different degrees of pressure. The inset is the zoom-in figure
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showing the I-V characteristics with the pressure from 40 to 100 kPa. (b) The
relationship between the sensitivity and the pressure in the pressing process. (c)
Real-time resistance change during 10000 cycles of pressure test for the pressure
sensor. (d) The zoom-in figure of Figure 4c showing 100 cycles of pressure and
resistance monitoring. (e) Real-time resistance response of the pressure sensor. (f) A
real-time resistance detection when a small pressure of 0.5 kPa is applied to the
sensor.
Figure 5 shows the influencing factors which are able to change the relative resistance
of the pressure sensor. A certain pressures of 13 kPa are applied with different
pressure velocities, as shown in Figure 5a. It can be seen that the pressure gradually
accelerate from 1st to 8th. The inset in Figure 5a shows the preset curve (red dashed
line) by the software, and the experimental curve (blue solid line) which represents
the actual pressure process by the universal material testing machine. Figure 5b shows
the relationship between R/R0 and pressure velocity. Each point in Figure 5b and the
maximum R/R0 of each curve in Figure 5a are corresponding to each other. It is
obvious that the values at different pressure velocities are almost the same. A series of
gradually increasing pressures were applied on the pressure sensor, as shown in
Figure 5c. It is found that the resistance change rises in a stair-like trend as the
pressure grows. Three different pressures are applied on the sensor cyclically in the
same way, as shown in Figure 5d, it is stable under the same pressure, and the stairs
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Figure 4. The pressure properties of the pressure sensor based on the CNC network. (a)
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resistance change of the pressure sensor is dependent only on the pressure levels,
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instead of the pressure velocities, indicating that the applying rate of the pressure does
not affect the output signals. This is of great importance for practical applications in
order to get a more reliable response.
Figure 5. The influencing factors of the pressure sensor relative resistance change. (a)
Relative resistance change versus a pressure of 13 kPa applied at different pressure
velocities. (b) The relationship between R/R0 and pressure rate corresponding to the
maximum R/R0 in Figure 5a. (c) Relative resistance change versus pressure from 1.25
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are obvious under different pressures. Combined with Figures 5a-d, the relative
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of 1.25, 8 and 13 kPa.
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The pressure sensor based on CNC network possesses a desirable integration of high
sensitivity and wide sensing range. In order to have a more intuitive impression on the
performance of the pressure sensor, its performance is comparable with those of
previously developed diverse flexible pressure sensors,1-4, 6, 10, 11, 13-20, 37-40 as shown in
Figure 6a. Several flexible pressure sensors are developed for high pressure detection,
which ranges from 10 to 100 kPa. However, most sensitivities of these sensors are not
very high, which are less than 10/kPa.13, 15, 16, 19, 37-40 Lipomi et al. reported a pressure
sensor with an excellent pressure limit of 1 MPa. However, the sensitivity of the
sensor is 2.3 × 10 −4 /kPa.20 Some pressure sensors owns a high sensitivity, but their
detection limit are very common. Pan et al. fabricated a kind of pressure sensor with
an ultrahigh sensitivity of 133/kPa, but the limit pressure can be detected by the
sensor is 20 kPa, so it cannot meet the needs of high pressure detection.17 It is worth
mentioning that some researches on the pressure sensor have achieved very good
performance. Zhou et al. reported a pressure sensor with an outstanding pressure limit
and high sensitivity of 900 kPa and 100/kPa, respectively.14 In this study, the pressure
sensor based on CNC network achieve a good balance between the limit of detection
and sensitivity, 100 kPa and 193/kPa, respectively. It is found that this sensor can
maintain ultrahigh sensitivity (>150/kPa) under high pressure environment (>50 kPa).
This demonstrates that the sensing capacity of the fabricated sensor can maintain good
performance in a wide pressure range.
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to 15 kPa in a stair-like trend. (d) Stair-like cycle pressure measure under the pressure
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of a pressure sensor, but there is no optimal value to compare the performances of
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different pressure sensor. The value of the sensitivity multiplied by the pressure can
be used to describe the performance of pressure sensor. However, the value is exactly
the amount of relative resistance change and both of the pressure and sensitivity are
ignored. Therefore, an equation where the relative resistance change (S×p) is
multiplied by the sensitivity can be defined to represent the performance of the
pressure sensor. So the optimal value of the pressure sensor can be expressed as,41
Optimal value = S2 × p
(11)
where S, p are the highest sensitivity, and the detection limit of a pressure sensor,
respectively. The optimal value of the sensor in this work, which is up to 3.72×106, is
300 times higher than most of the current pressure sensors, as shown in Figure 6b. It
illustrates that the pressure sensor based on CNC network achieves a good balance
between high sensitivity and high detection limit.
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In general, the sensitivity and detection limit can be used to represent the performance
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the pressure sensor based on CNC network with those of conventional pressure
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sensors.
As a demonstration of pressure detection in real time, this CNC network based
pressure sensor was placed on a horizontal surface, and then tapped on the sensor
surface with the finger while monitoring the resistance change. Each group contains 5
consecutive tappings, and the results are shown in Figure 7a and Supplementary
Movie 1. It can be seen from Figure 7d that each group of tappings can be detected. It
is worth noting that 5 times of tappings in the same group can be clearly distinguished,
indicating a high precision and sensitivity of the sensor, as shown in the inset of
Figure 7d. Figure 7b and Figure 7e show that the pressure sensor is used to monitor
regular vibrations. The sensor is attached to the surface of a mobile phone screen.
Then the mobile phone was set to the state of cyclic vibration-static, at the same time,
the resistance change of the pressure sensor was monitored (Supplementary Movie 2).
It is found that this regular vibration can be clearly detected, and the resistance
changes of each vibration are in the same range. In addition, this pressure sensor can
also detect the air pressure applied on its surface, as shown in Figure 7c and
Supplementary Movie 3. It is observed from Figure 7f that each time of the blowing
can be clearly detected with short response time.
20
Journal of Materials Chemistry C Accepted Manuscript
Figure 6. Comparison of (a) the sensitivity, detection limit and (b) optimal value of
Page 21 of 26
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Figure 7. Some photos of the applications, such as (a) tapping detection, (b) mobile
phone vibration detection, and (c) air pressure detection. The real-time monitoring of
(d) tapping detection, (e) mobile phone vibration, and (f) air pressure detection.
4. Conclusion
In this work, a kind of wide range pressure sensor was fabricated with PDMS as the
flexible substrate and the CNC network as the conductive medium. The sensor can
withstand a pressure limit of 100 kPa, clearly distinguish a minimum pressure of 0.5
kPa, and has an ultrahigh sensitivity of 193/kPa at the pressure of 70 kPa. A high
stability and reproducibility of 10000 cycles, and a fast response time of less than
48 ms have been achieved. A concept of optimal value that can evaluate the
performances of different pressure sensors is proposed, and the optimal value of this
sensor is up to 3.72×106, which is 300 times higher than most of the current pressure
sensors. The pressure sensor shows a great potential in the field of pressure detection
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DOI: 10.1039/C7TC04166G
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DOI: 10.1039/C7TC04166G
resistance to pressure.
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Acknowledgments
This work was supported by the National Natural Science Foundation of China (No.
51661145025, 11274055, 61520106013).
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Figure 1. The fabrication process of the pressure sensor based on CNC network.
Figure 2. The electrophoresis process of the CNC network between the comb-shaped
electrodes. (a) - (c) The distribution of the CNCs between the comb-shaped electrodes
with the increase of the electrophoresis progress in the optical microscope. (d) The
SEM image of the distribution of the CNCs between several pairs of the comb-shaped
electrodes after electrophoresis. (e) The distribution of CNCs between one pair of the
electrodes. (f) The connection between the CNCs and electrode. (g) The cross section
image of the CNCs between one pair of the electrodes before encapsulation. (h) The
relationship between the resistance of the CNC network and the times of
electrophoresis.
Figure 3. The resistance change of the pressure sensor during the pressing process. (a)
The relationship between R/R0 and pressure. The inset is the linear relationship
between the logarithm of R/R0 and pressure in stage 1. (b) The schematic of the sensor
resistance change under light pressure and high pressure.
Figure 4. The pressure properties of the pressure sensor based on the CNC network. (a)
I-V characteristics under different degrees of pressure. The inset is the zoom-in figure
showing the I-V characteristics with the pressure from 40 to 100 kPa. (b) The
relationship between the sensitivity and the pressure in the pressing process. (c)
Real-time resistance change during 10000 cycles of pressure test for the pressure
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Journal of Materials Chemistry C Accepted Manuscript
Figure captions
Journal of Materials Chemistry C
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resistance monitoring. (e) Real-time resistance response of the pressure sensor. (f) A
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real-time resistance detection when a small pressure of 0.5 kPa is applied to the
sensor.
Figure 5. The influencing factors of the pressure sensor relative resistance change. (a)
Relative resistance change versus a pressure of 13 kPa applied at different pressure
velocities. (b) The relationship between R/R0 and pressure rate corresponding to the
maximum R/R0 in Figure 5a. (c) Relative resistance change versus pressure from 1.25
to 15 kPa in a stair-like trend. (d) Stair-like cycle pressure measure under the pressure
of 1.25, 8 and 13 kPa.
Figure 6. Comparison of (a) the sensitivity, detection limit and (b) optimal value of
the pressure sensor based on CNC network with those of conventional pressure
sensors.
Figure 7. Some photos of the applications, such as (a) tapping detection, (b) mobile
phone vibration detection, and (c) air pressure detection. The real-time monitoring of
(d) tapping detection, (e) mobile phone vibration, and (f) air pressure detection.
26
Journal of Materials Chemistry C Accepted Manuscript
sensor. (d) The zoom-in figure of Figure 4c showing 100 cycles of pressure and
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