Chapter 7
Flexible and Stretchable Sensors
Flexible and Stretchable Electronics: Materials, Design, and Devices
Edited by Run-Wei Li and Gang Liu
Copyright © 2019 Jenny Stanford Publishing Pte. Ltd.
ISBN 978-981-4800-46-4 (Hardcover), 978-0-429-05890-5 (eBook)
Tie Li,† Yudong Cao, Chunyan Qu, and Ting Zhang
i-Lab, Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO),Chinese Academy of Sciences (CAS), 398 Ruoshui Road, Suzhou,215123, P. R. China
tzhang2009@sinano.ac.cn

Currently, flexible electronics provide the most exciting frontier for next-generation devices in both circuits and wearable/portable devices due to their unique properties, such as strong stretchability and flexibility, which allows the board to conform to any aspiring shapes for space saving. Specially, smart and multifunctional, flexible and stretchable sensors broaden the place where electronic devices would be used, making the device usable in wearable healthmonitoring system, cost-effective disease diagnosis in telemedicine, and medicine robots and prosthetics. To meet those special characters and requirements, in the past 10 years, various strategies of structural design and functional materials have been employed for the realization of flexibility and stretchability in sensors. To showcase an overview of the development of flexible electronics that have advanced in the past years and have made great changes in our daily life, we discuss classes of structure, materials, and applications covering several critical aspects of flexible and stretchable sensors.

7.1 Introduction

Flexible and/or stretchable electronics, such as stretchable transistors, smart flexible sensors, stretchable energy harvesters and energy storage devices, have intensively obtained a great deal of attraction due to their high performance and elastic mechanical responses, which possess vast potential demand for flexible, lightweight, and mobile electronics that can be used in various areas containing robotic sensory skins, healthcare monitoring, bio-integrated devices, human–machine interfaces, wearable communication devices, and so on [1–8]. Especially, the rapid advances in the design of various flexible and/or stretchable sensors, which can be integrated in curved surfaces such as touchscreen, flexible displays, and even human body, have tremendously broadened the scope of flexible electronics to new classes of soft electronic systems [9, 10]. For example, these flexible sensors could help the electronic devices understand how real-world objects “feel” during interactions and also obtain biosignals such as finger touching and body motions [11, 12]. Further, compliant wearable flexible sensor systems have the potential to interface better with human skin, thus improving the sensitivity of detection of health indicators [13, 14]. In addition, flexible and/or stretchable sensors in large-area arrays have also been developed to mimic the properties of natural existed structure or feature with multiple functionalities, which may enable promising applications in emerging Internet of Things such that people, processes, data, and devices are integrated and connected to improve the quality of life [15–17]. The most crucial challenges in the development of flexible and stretchable sensors are the simultaneous achievement of both favorable mechanically durable materials and robust flexible and stretchable substrates, deformable electrodes and circuits, novel processing methods, and system integration [18]. In the past decade, rapid developments in new nanomaterials, new concepts in structural design, fabrication techniques, and original applications have contributed to significant progress in the achievement of flexible and stretchable sensors [19]. Specifically, constituent materials and devices in stretchable integrated systems must be designed so that their mechanical and electrical functionality is preserved under high strain values [20]. For example, the emerging nanostructured material, graphene, which possesses unique mechanical, electrical, and optical properties, is an attractive candidate for combination with flexible and stretchable polymeric substrates such as poly(ethylene terephthalate) (PET), polyethylenimine (PEI), or poly(dimethylsiloxane) (PDMS) for producing various flexible and/or stretchable sensors such as flexible pressure sensor, stretchable fiber strain sensor, flexible optoelectronic and energyharvesting devices, and so on [21–28]. Moreover, the combination of the aforementioned graphene-based flexible and stretchable sensors with low-power silicon-based electronics can also lead to the development of new wearable electronics, which are driven by improved three-dimensional (3D) interpenetration ability of soft electronic systems and flexible or stretchable electronic systems[29, 30]. To provide an overview of flexible and stretchable electronics that have advanced and made great changes in our daily life in the past few years, we present this chapter covering the following critical aspects of flexible and stretchable sensors.