Citation: Park, C.; Choi, M.; Lee, S.;
Kim, H.; Lee, T.; Billah, M.M.; Jung,
B.; Jang, J. Highly Sensitive,
Stretchable Pressure Sensor Using
Blue Laser Annealed CNTs.
Nanomaterials 2022, 12, 2127.
https://doi.org/10.3390/
nano12132127
Academic Editor: Shiqiang (Rob) Hui
Received: 23 May 2022
Accepted: 16 June 2022
Published: 21 June 2022
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Article
Highly Sensitive, Stretchable Pressure Sensor Using Blue Laser
Annealed CNTs
Chanju Park , Munsu Choi, Suhui Lee, Hyunho Kim, Taeheon Lee, Mohammad Masum Billah , Byunglib Jung
and Jin Jang *
Advanced Display Research Center (ADRC), Department of Information Display, Kyung Hee University,
26 Kyungheedae-ro, Dongdaemun-gu, Seoul 02447, Korea; cjpark@tft.khu.ac.kr (C.P.);
mschoi@tft.khu.ac.kr (M.C.); shlee5@tft.khu.ac.kr (S.L.); hhkim@tft.khu.ac.kr (H.K.); thlee@tft.khu.ac.kr (T.L.);
masum@tft.khu.ac.kr (M.M.B.); bljung@tft.khu.ac.kr (B.J.)
* Correspondence: jjang@khu.ac.kr
Abstract:
A piezoresistive sensor is an essential component of wearable electronics that can detect
resistance changes when pressure is applied. In general, microstructures of sensing layers have been
adopted as an effective approach to enhance piezoresistive performance. However, the mold-casted
microstructures typically have quite a thick layer with dozens of microscales. In this paper, a carbon
microstructure is formed by blue laser annealing (BLA) on a carbon nanotube (CNT) layer, which
changes the surface morphology of CNTs into carbonaceous protrusions and increases its thickness
more than four times compared to the as-deposited layer. Then, the pressure sensor is fabricated
using a spin-coating of styrene–ethylene–butylene–styrene (SEBS) elastomer on the BLA CNTs layer.
A 1.32
µ
m-thick pressure sensor exhibits a high sensitivity of 6.87
×
10
5
kPa
−1
, a wide sensing
range of 278 Pa~40 kPa and a fast response/recovery time of 20 ms, respectively. The stability of the
pressure sensor is demonstrated by the repeated loading and unloading of 20 kPa for 4000 cycles.
The stretchable pressure sensor was also demonstrated using lateral CNT electrodes on SEBS surface,
exhibiting stable pressure performance, with up to 20% stretching.
Keywords: pressure sensor; carbon nanotube (CNT); blue laser annealing (BLA)
1. Introduction
The pressure sensor is of increasing interest because of its various applications, such
as object detection, display touch, electronic skin (e-skin), etc. [
1
–
3
]. Mobile and health-
care devices with touch sensors are used in human activities [
4
,
5
]. The demand for the
development of pressure sensors, converting the external stimulus into electrical signals,
is continuously increasing [
6
–
8
]. In general, the pressure sensors can be classified as
piezoresistive [9–16], capacitive [17–23], and piezoelectric types [24–28].
Among them, piezoresistive-type pressure sensors operate on a simple principle
that detects the resistance change under applied pressure [
14
–
16
]. Usually, conductive
fillers such as carbon nanotubes (CNTs) [
9
,
10
,
14
], graphenes [
29
], nanoparticles [
30
–
32
],
and nanowires [
16
,
33
] have been used to fabricate piezoresistive pressure sensors. How-
ever, polymer-composite-film-based piezoresistive pressure sensors typically have the
disadvantage of low sensitivity. Therefore, pressure sensors with porous structure [17,34],
microstructure [13,35–37], and pyramid structure [38–41] have been developed to achieve
improved sensitivity and response time. The microstructure efficiently modulates the
contact resistance and improves the response and recovery speed and the stability of the
pressure sensor. A piezoresistive pressure sensor with high sensitivity over 1000 kPa
−1
typically has high initial resistance and large pressure-sensitive current deviation, which
are essential requirements for high sensitivity [
36
,
37
,
40
,
41
]. Recently, ultra-high-sensitive
pressure sensors with sensitivities of 10
5
–10
6
kPa
−1
were demonstrated [
42
–
44
]. The strat-
egy for achieving ultra-high sensitivity is based on a microstructure sensing layer. Li et al.
Nanomaterials 2022, 12, 2127. https://doi.org/10.3390/nano12132127 https://www.mdpi.com/journal/nanomaterials
