Stretchable Electronics

Takao Someya

• Publisher: Wiley-VCH
• Year: 2012
• Print ISBN: 9783527329786
• eBook ISBN: 9783527647002
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

On a daily basis, our requirements for technology become more innovative and creative and the field of electronics is helping to lead the
way to more advanced appliances. This book gathers and evaluates the materials, designs, models, and technologies that enable the fabrication of fully elastic electronic devices that can tolerate high strain. Written by some of the most outstanding scientists in the field, it lays down the undisputed knowledge on how to make electronics withstand stretching. This monograph provides a review of the specific applications that directly benefit from highly compliant electronics, including transistors, photonic devices, and sensors. In addition to stretchable devices, the topic of ultraflexible electronics is treated, highlighting its upcoming significance for the industrial-scale production of electronic goods for the consumer.

Divided into four parts covering:

* Theory
* Materials and Processes
* Circuit Boards
* Devices and Applications

An unprecedented overview of this thriving area of research that nobody in the field - or intending to enter it - can afford to miss.

Part I
Theory

1

Theory for Stretchable Interconnects

Jizhou Song and Shuodao Wang

1.1 Introduction

A rapidly growing range of applications demand electronic systems that cannot be formed in the conventional manner on semiconductor wafers. The most prominent example is stretchable electronics, which has a performance equal to established technologies that use rigid semiconductor wafers, but in formats that can be stretched and compressed. It enables many application possibilities such as flexible displays [1], electronic eye camera [2–4], conformable skin sensors [5], smart surgical gloves [6], and structural health monitoring devices [7]. There are primarily two directions to make stretchable electronics. One is to use intrinsically stretchable materials such as organic materials [8–13]. However, the electrical per­formance of organic semiconductor materials is relatively poor comparing with the well-developed, high-performance inorganic electronic materials. The other direction to achieve stretchable electronics is to use conventional semiconductors, such as silicon, and make the system stretchable. The main challenge here is to make silicon-based structures stretchable since the brittleness of silicon makes it almost impossible to be stretched. Many researches bypassed this difficulty by using stretchable interconnects [14–22].

One of the most intuitive approaches to develop stretchable interconnects is to exploit out-of-plane deflection in thin layers to accommodate strains applied in the plane. Figure 1.1 illustrates some examples of this concept. In the first case (Figure 1.1a) [17, 24, 25] of stretchable wavy ribbons, the initially flat ribbons are bonded to a prestrained elastomeric substrate. The prestrain can be induced by mechanical (or thermal) stretch along the ribbon directions. Releasing the prestrain causes a compression in the ribbon, and this compression leads to a nonlinear buckling response and results in a wavy profile. When the wavy structure is subject to stretches, the amplitudes and periods of the waves change to accommodate the deformation. In the second case (Figure 1.1b) of popup structure [26], the ribbons can be designed to bond the prestretched elastomeric substrate only at certain locations. When the prestrain is released, the ribbon on the nonbonded regions delaminates from the substrate and forms popup profile. Compared to Figure 1.1a, this layout has the advantage that the wavelengths can be defined precisely with a level of engineering control to have higher stretchability.

Figure 1.1 SEM images of (a) stretchable wavy ribbons, (b) popup structure, (c) noncoplanar mesh design with straight interconnects, and (d) noncoplanar mesh design with serpentine interconnects.

(Reprinted with permission from Ref. [15] Copyright 2007 American Institute of Physics and Ref. [23] Copyright 2009 American Vacuum Society).

Combining the stretchable interconnects in Figure 1.1a (or Figure 1.1b) with rigid device islands, an interconnect-island structure [16, 19, 20, 22] can be developed to accommodate the deformations. Mechanical response to stretching or compression involves, primarily, deformations only in these interconnects, thereby avoiding unwanted strains in the regions of the active devices. Lacour et al. [16] and Kim et al. [19] developed a coplanar mesh design by using the wavelike interconnects, which are bonded with the substrate. Although such a coplanar mesh design can improve the stretchability...

Table of contents

• Cover
• Related Titles
• Title page
• Copyright page
• Preface
• List of Contributors
• Part I: Theory
• Part II: Materials and Processes
• Part III: Circuit Boards
• Part IV: Devices and Applications
• Index