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SCIENCE CHINA Materials, Volume 61, Issue 12: 1587-1595(2018) https://doi.org/10.1007/s40843-018-9267-3

Flexible and transparent capacitive pressure sensor with patterned microstructured composite rubber dielectric for wearable touch keyboard application

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  • ReceivedFeb 14, 2018
  • AcceptedMar 28, 2018
  • PublishedApr 27, 2018

Abstract

The development of pressure sensors with highly sensitivity, fast response and facile fabrication technique is desirable for wearable electronics. Here, we successfully fabricated a flexible transparent capacitive pressure sensor based on patterned microstructured silver nanowires (AgNWs)/polydimethylsiloxane (PDMS) composite dielectrics. Compared with the pure PDMS dielectric layer with planar structures, the patterned microstructured sensor exhibits a higher sensitivity (0.831 kPa−1, <0.5 kPa), a lower detection limit, good stability and durability. The enhanced sensing mechanism about the conductive filler content and the patterned microstructures has also been discussed. A 5×5 sensor array was then fabricated to be used as flexible and transparent wearable touch keyboards systems. The fabricated pressure sensor has great potential in the future electronic skin area.


Funded by

the National Science Foundation for Distinguished Young Scholars of China(NSFC,61625404)

the Key Research Program of Frontier Sciences

CAS(QYZDY-SSW-JWC004)

the NSFC(61504136)


Acknowledgment

This work was supported by the National Natural Science Foundation for Distinguished Young Scholars of China (NSFC, 61625404), the Key Research Program of Frontier Sciences, CAS (QYZDY-SSW-JWC004) and the NSFC (61504136).


Interest statement

The authors declare no conflict of interest.


Contributions statement

Shi R and Lou Z designed the devices and experiments; Shi R performed the experiments; Shi R, Lou Z and Chen S analyzed the data; Shi R and Chen S synthesized the Ag nanowires; Shi R wrote the paper with support from Lou Z and Chen S. All authors contributed to the general discussion.


Author information

Ruilong Shi received his BSc degree from Jilin University in 2015. Now he is a graduate student at the Institute of Semiconductors, Chinese Academy of Sciences. His research interest focuses on flexible pressure sensor and wearable electronic devices.


Zheng Lou received his PhD degree from Jilin University in 2014. He joined the Institute of Semiconductors, Chinese Academy of Sciences as an Assistant Professor in 2014 and was promoted to Associate Professor in 2018. His current research focuses on flflexible electronics, including pressure sensors, electronic-skin, transistors and photo-detectors.


Guozhen Shen received his BSc degree in 1999 from Anhui Normal University and PhD degree in 2003 from the University of Science and Technology of China. From 2004 to 2013, he conducted his research in Hanyang University (Korea), National Institute for Materials Science (Japan), University of Southern California (USA) and Huazhong University of Science and technology. He joined the Institute of Semiconductors, Chinese Academy of Sciences as a professor in 2013. His current research focuses on flexible electronics and printable electronics, including transistors, photodetectors, sensors and flexible energy-storage devices.


Supplement

Supplementary information

Supporting data are available in the online version of the paper.


References

[1] Lou Z, Chen S, Wang L, et al. Ultrasensitive and ultraflexible e-skins with dual functionalities for wearable electronics. Nano Energy, 2017, 38: 28-35 CrossRef Google Scholar

[2] Khan Y, Ostfeld AE, Lochner CM, et al. Monitoring of vital signs with flexible and wearable medical devices. Adv Mater, 2016, 28: 4373-4395 CrossRef PubMed Google Scholar

[3] Hammock ML, Chortos A, Tee BCK, et al. 25th anniversary article: the evolution of electronic skin (e-skin): a brief history, design considerations, and recent progress. Adv Mater, 2013, 25: 5997-6038 CrossRef PubMed Google Scholar

[4] Wang L, Jackman JA, Tan EL, et al. High-performance, flexible electronic skin sensor incorporating natural microcapsule actuators. Nano Energy, 2017, 36: 38-45 CrossRef Google Scholar

[5] Chen S, Lou Z, Chen D, et al. Polymer-enhanced highly stretchable conductive fiber strain sensor used for electronic data gloves. Adv Mater Technol, 2016, 1: 1600136 CrossRef Google Scholar

[6] Lou Z, Chen S, Wang L, et al. An ultra-sensitive and rapid response speed graphene pressure sensors for electronic skin and health monitoring. Nano Energy, 2016, 23: 7-14 CrossRef Google Scholar

[7] Kim CC, Lee HH, Oh KH, et al. Highly stretchable, transparent ionic touch panel. Science, 2016, 353: 682-687 CrossRef PubMed ADS Google Scholar

[8] Lee J, Kwon H, Seo J, et al. Conductive fiber-based ultrasensitive textile pressure sensor for wearable electronics. Adv Mater, 2015, 27: 2433-2439 CrossRef PubMed Google Scholar

[9] Wang L, Jackman JA, Ng WB, et al. Flexible, graphene-coated biocomposite for highly sensitive, real-time molecular detection. Adv Funct Mater, 2016, 26: 8623-8630 CrossRef Google Scholar

[10] Wang L, Chen D, Jiang K, et al. New insights and perspectives into biological materials for flexible electronics. Chem Soc Rev, 2017, 46: 6764-6815 CrossRef PubMed Google Scholar

[11] Wang L, Jackman JA, Park JH, et al. A flexible, ultra-sensitive chemical sensor with 3D biomimetic templating for diabetes-related acetone detection. J Mater Chem B, 2017, 5: 4019-4024 CrossRef Google Scholar

[12] Wang L, Ng WB, Jackman JA, et al. Graphene-functionalized natural microcapsules: modular building blocks for ultrahigh sensitivity bioelectronic platforms. Adv Funct Mater, 2016, 26: 2097-2103 CrossRef Google Scholar

[13] Chou HH, Nguyen A, Chortos A, et al. A chameleon-inspired stretchable electronic skin with interactive colour changing controlled by tactile sensing. Nat Commun, 2015, 6: 8011 CrossRef PubMed ADS Google Scholar

[14] Pang C, Koo JH, Nguyen A, et al. Highly skin-conformal microhairy sensor for pulse signal amplification. Adv Mater, 2015, 27: 634-640 CrossRef PubMed Google Scholar

[15] Lee BY, Kim J, Kim H, et al. Low-cost flexible pressure sensor based on dielectric elastomer film with micro-pores. Sensor Actuat A-Phys, 2016, 240: 103-109 CrossRef Google Scholar

[16] Chen YS, Hsieh GW, Chen SP, et al. Zinc oxide nanowire-poly(methyl methacrylate) dielectric layers for polymer capacitive pressure sensors. ACS Appl Mater Interfaces, 2015, 7: 45-50 CrossRef PubMed Google Scholar

[17] Kim SY, Park S, Park HW, et al. Highly sensitive and multimodal all-carbon skin sensors capable of simultaneously detecting tactile and biological stimuli. Adv Mater, 2015, 27: 4178-4185 CrossRef PubMed Google Scholar

[18] Guo X, Huang Y, Cai X, et al. Capacitive wearable tactile sensor based on smart textile substrate with carbon black /silicone rubber composite dielectric. Meas Sci Technol, 2016, 27: 045105 CrossRef ADS Google Scholar

[19] Lee D, Lee H, Jeong Y, et al. Highly sensitive, transparent, and durable pressure sensors based on sea-urchin shaped metal nanoparticles. Adv Mater, 2016, 28: 9364-9369 CrossRef PubMed Google Scholar

[20] Li T, Luo H, Qin L, et al. Flexible capacitive tactile sensor based on micropatterned dielectric layer. Small, 2016, 12: 5042-5048 CrossRef PubMed Google Scholar

[21] Tee BCK, Chortos A, Dunn RR, et al. Tunable flexible pressure sensors using microstructured elastomer geometries for intuitive electronics. Adv Funct Mater, 2014, 24: 5427-5434 CrossRef Google Scholar

[22] Mannsfeld SCB, Tee BCK, Stoltenberg RM, et al. Highly sensitive flexible pressure sensors with microstructured rubber dielectric layers. Nat Mater, 2010, 9: 859-864 CrossRef PubMed ADS Google Scholar

[23] Zhuo B, Chen S, Zhao M, et al. High sensitivity flexible capacitive pressure sensor using polydimethylsiloxane elastomer dielectric layer micro-structured by 3-D printed mold. IEEE J Electron Devices Soc, 2017, 5: 219-223 CrossRef Google Scholar

[24] Mi Y, Chan Y, Trau D, et al. Micromolding of PDMS scaffolds and microwells for tissue culture and cell patterning: A new method of microfabrication by the self-assembled micropatterns of diblock copolymer micelles. Polymer, 2006, 47: 5124-5130 CrossRef Google Scholar

[25] Chen S, Zhuo B, Guo X. Large area one-step facile processing of microstructured elastomeric dielectric film for high sensitivity and durable sensing over wide pressure range. ACS Appl Mater Interfaces, 2016, 8: 20364-20370 CrossRef Google Scholar

[26] Schwartz G, Tee BCK, Mei J, et al. Flexible polymer transistors with high pressure sensitivity for application in electronic skin and health monitoring. Nat Commun, 2013, 4: 1859 CrossRef PubMed ADS Google Scholar

[27] Pan L, Chortos A, Yu G, et al. An ultra-sensitive resistive pressure sensor based on hollow-sphere microstructure induced elasticity in conducting polymer film. Nat Commun, 2014, 5: 3002 CrossRef PubMed ADS Google Scholar

[28] Boutry CM, Nguyen A, Lawal QO, et al. A sensitive and biodegradable pressure sensor array for cardiovascular monitoring. Adv Mater, 2015, 27: 6954-6961 CrossRef PubMed Google Scholar

[29] Xu J, Wong M, Wong C. Super high dielectric constant carbon black-filled polymer composites as integral capacitor dielectrics. 54th Electronic Components and Technology Conference (IEEE Cat. No.04CH37546), 2004, 1: 536-541 CrossRef Google Scholar

[30] Kirkpatrick S. The nature of percolation ‘channels’. Solid State Commun, 1973, 12: 1279-1283 CrossRef ADS Google Scholar

[31] Zallen R. The formation of amorphous solids. In The Physics Of Amorphous Solids. New Jersey: Wiley-VCH, 1983, 1-32. Google Scholar

[32] Pecharromán C, Moya JS. Experimental evidence of a giant capacitance in insulator-conductor composites at the percolation threshold. Adv Mater, 2000, 12: 294-297 CrossRef Google Scholar

  • Figure 1

    Schematic illustration for the fabrication of (a) micropatterned Si mould and (b) flexible microstructured AgNWs/PDMS composite dielectric film.

  • Figure 2

    (a) Architecture of the flexible capacitive pressure sensor. (b) The photo image of a single pressure sensor device. (c) Top and (d) tilted SEM images of the micro-structured AgNWs/PDMS film. (e) Optical transmittance of the AgNWs/PDMS films with various mixing ratios of AgNWs.

  • Figure 3

    (a) Schematic illustration of the sensing mechanism of the capacitive pressure sensor. (b) Capacitance changes of the non-patterned sensors under pressure with various mixing ratios of AgNWs. (c, d) Sensitivity curves of the pressure sensor with different types of dielectric layer under applied pressure. The micro-structured sensor based on AgNWs/PDMS dielectric layer with 0.12 wt% AgNWs exhibits higher pressure sensitivity than that based on the non-patterned or micro-structured PDMS dielectric layer without AgNWs. (e) Comparison of the sensing performance of our work and previous research results [8,17,19,20,22,25,27,28].

  • Figure 4

    Characterization of capacitive pressure response of the sensor with the microstructured 0.12 wt% AgNWs/PDMS dielectric layer. (a) Reliable capacitance change of the sensor under different pressures. (b) Repeated real-time response curves of both types of micro-structured sensors under pressures of 0.1 kPa and 0.2 kPa, respectively. (c) Fast response time (<30 ms) and relaxation time of the sensor. (d) Transient response to the placing and removal of a small piece of paper, the first corresponding to a pressure of only 1.4 Pa. (e) Capacitance change curves recorded after 1,000, 2,000, 5,000, 7,000 and 10,000 cycles, respectively under a pressure of 1 kPa. (f) Magnified view of (e) after 7,000 loading-unloading cycles.

  • Figure 5

    (a) Schematic illustration of the final flexible e-skin device and an enlarged pixel with a sandwich structure. (b) System-level block diagram of the wireless printed circuit board (PCB) showing the signal switching, conditioning, processing and wireless transmission paths from sensors to the mobile application (numbers in parentheses indicate the corresponding labelled components in the photo of the wireless PCB). The flexible sensor array is able to achieve the function of the keyboard (c). Demonstrations such as real-time inputting word “f” (d) and “flextronics” (e) are shown in the mobile application.

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