Flexible and Stretchable Medical Devices

Kuniharu Takei

• Publisher: Wiley-VCH
• Year: 2018
• Print ISBN:
  9783527341832
• Edition: 1
• eBook ISBN:
  9783527804863
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

The book introduces flexible and stretchable wearable electronic systems and covers in detail the technologies and materials required for healthcare and medical applications. A team of excellent authors gives an overview of currently available flexible devices and thoroughly describes their physical mechanisms that enable sensing human conditions.
In dedicated chapters, crucial components needed to realize flexible and wearable devices are discussed which include transistors and sensors and deal with memory, data handling and display. Additionally, suitable power sources based on photovoltaics, thermoelectric energy and supercapacitors are reviewed. A special chapter treats implantable flexible sensors for neural recording.
The book editor concludes with a perspective on this rapidly developing field which is expected to have a great impact on healthcare in the 21st century.

Chapter 1
History of Flexible and Stretchable Devices

Kuniharu Takei

Osaka Prefecture University, Department of Physics and Electronics, 1-1 Gakuen Nakaku, Sakai, Osaka, 599-8531, Japan

Flexible devices such as transistors and transducers have been developed since 1990 by forming organic thin film or transferring inorganic thin film on plastic substrates. From the 1990s to the early 2000s, flexible transistors and light emitting diodes (LEDs) were mainly developed on a flexible substrate using organic materials because organic materials are fundamentally mechanically flexible compared to inorganic films and can be formed by using solution-based or evaporation processes on amorphous plastic substrates [1–4]. However, by utilizing inorganic thin film transfer technique from a bulk wafer to another substrate that was developed by Konagai et al. [5] and Yablonovitch et al. [6], inorganic-based flexible devices have been also developed since 2000 [7–15]. During the early stages of development of flexible electronics, the fundamental characteristics of devices such as transistors and sensors with relevance to organic and inorganic materials, their electrical characteristics, mechanical reliability, and bendability were deeply studied [7–10]. Although the fundamental properties using similar material systems as well as new material systems are still being investigated [16, 17], the approach for flexible and stretchable electronics is now to develop flexible and/or stretchable device applications [11–15, 17–34]. As device integrations on flexible substrate, Rogers et al. developed a paper-like electronic display using organic material-based active matrix backplane in 2001, which was most likely the first demonstration of the material integration for flexible device applications [4]. Following this development, Someya et al. demonstrated an artificial electronic skin (e-skin) to detect pressure distributions similar to that in human skin in 2004 [35], and in 2005, his group further developed a pressure and temperature distribution sensing device using organic-based thin film transistors (TFTs) for the active matrix backplane [36]. At the same time, thin film Si TFTs were transferred from silicon-on-insulator (SOI) wafer to a flexible substrate, which allows it to operate TFTs with high mobility and high stability in ambient air [8, 10]. During the 2000s, one of the bottlenecks for flexible electronics using organic materials as the active component was low performance and instability in ambient air. However, subsequent to the demonstration of inorganic-based TFTs, possibilities arose for inorganic material to be flexible electronics. Since the Si-based TFTs are a matured technique as the industrial standard for Si-based integrated circuits (ICs), the properties of flexible Si-TFTs show a great performance with a field-effect mobility of 180 cm²/Vs on a flexible substrate [8]. In 2008, Rogers et al. successfully fabricated a highly integrated digital circuit of a four-bit row decoder using carbon nanotube networks as p-type transistors [13]. After several developments of inorganic material formations, device structures, and new organic materials, flexible transistors using both organic and inorganic materials have displayed high potential for flexible electronics due to improvements in their performance and stability. Using the platforms of organic transistors and organic light emitting diodes (OLEDs), active matrix OLED flexible display was demonstrated by Someya et al. [37]. In 2010, two e-skin device demonstrations were reported at the same time by Bao et al. [19] and Javey et al. [20]. Each e-skin has unique structures. The device reported by Javey et al. has an inorganic nanowire array active matrix backplane to show high flexibility and performance realized by nanowire printing technique [20], and Bao et al. proposed a unique structure to detect tactile pressure with high sensitivity [19]. The flexible and stretchable devices were then applied to medical and neuroscience fields for implantation or in vivo experiments by utilizing their flexibility [18, 38–40]. One interesting approach is to use the material such as silk dissolved in water [18, 39]. This eventually allows it to use the sensors and curing devices for the implantation, and it is not necessary to remove it after surgery and curing because it is dissolved in the body, which helps to reduce medical cost and patient load for re-surgery. Subsequent to these developments, many kinds of flexible and stretchable device applications have been developed to date, such as self-healing sensors [23], ultrathin flexible devices [41], photovoltaics devices [30]. In addition, recently, fully printed, multifunctional, low-cost, wearable flexible healthcare devices have been also reported by integrating with multiple sensors for healthcare detections and human activity [42]. However, many demonstrations were often focused on the sensor and transistor integration on flexible and stretchable substrates, and there were still challenges toward moving forward for realizing practical applications. The biggest problem of these devices is how to realize signal processing circuits, wireless systems, and battery because flexible transistors are not capable of building complicated circuits although there has been significant improvements and developments from many groups. To overcome this challenge, in 2016, Javey et al. demonstrated a hybrid system integrating flexible chemical sensors and inflexible conventional ICs for signal processing of the sensing results and a wireless system on a flexible printed circuit film [34]. Furthermore, Rogers et al. also developed the battery-free hybrid system to monitor health conditions wirelessly by integrating flexible and stretchable antenna and chip-based circuits [43].

In this book, the fundamental physics of electrical components such as flexible and stretchable transistors, memories, and sensors are first introduced to understand the present status of the flexible and...

Table of contents

• Cover
• Title Page
• Copyright
• Table of Contents
• Preface
• Acknowledgments
• Chapter 1: History of Flexible and Stretchable Devices
• Chapter 2: Carbon Nanotube Based Flexible and Stretchable Electronics
• Chapter 3: Organic-Based Transistors and Sensors
• Chapter 4: Printed Transistors and Sensors
• Chapter 5: Flexible Photovoltaic Systems
• Chapter 6: Materials Design for Flexible Thermoelectric Power Generators
• Chapter 7: Flexible Supercapacitors Based on Two-Dimensional Materials
• Chapter 8: Organometal Halide Perovskites for Next Generation Fully Printed and Flexible LEDs and Displays
• Chapter 9: Flexible Floating Gate Memory
• Chapter 10: Flexible and Stretchable Wireless Systems
• Chapter 11: Conductive Nanosheets for Ultra-Conformable Smart Electronics
• Chapter 12: Flexible Health-Monitoring Devices/Sensors
• Chapter 13: Stretchable Health Monitoring Devices/Sensors
• Chapter 14: Flexible/Stretchable Devices for Medical Applications
• Chapter 15: Implantable Flexible Sensors for Neural Recordings
• Chapter 16: Perspective in Flexible and Stretchable Electronics
• Index
• End User License Agreement