Handbook of Flexible Organic Electronics

Materials, Manufacturing and Applications

Stergios Logothetidis

• Publisher: Woodhead Publishing
• Year: 2014
• Print ISBN: 9781782420354
• eBook ISBN: 9781782420439
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Organic flexible electronics represent a highly promising technology that will provide increased functionality and the potential to meet future challenges of scalability, flexibility, low power consumption, light weight, and reduced cost. They will find new applications because they can be used with curved surfaces and incorporated in to a number of products that could not support traditional electronics. The book covers device physics, processing and manufacturing technologies, circuits and packaging, metrology and diagnostic tools, architectures, and systems engineering. Part one covers the production, properties and characterisation of flexible organic materials and part two looks at applications for flexible organic devices. - Reviews the properties and production of various flexible organic materials. - Describes the integration technologies of flexible organic electronics and their manufacturing methods. - Looks at the application of flexible organic materials in smart integrated systems and circuits, chemical sensors, microfluidic devices, organic non-volatile memory devices, and printed batteries and other power storage devices.

Part One

Properties and materials

Outline

1. Mechanics of curvature and strain in flexible organic electronic devices

2. Structural and electronic properties of fullerene-based organic materials: density functional theory-based calculations

3. Hybrid and nanocomposite materials for flexible organic electronics applications

4. Organic polymeric semiconductor materials for applications in photovoltaic cells

1

Mechanics of curvature and strain in flexible organic electronic devices

Y. Leterrier Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland

Abstract

This chapter introduces basic mechanical concepts and provides key ingredients for rational design of flexible organic electronics based on multilayer film structures. The failure of thin films under tensile and compressive loading is examined first, with focus on critical strain, critical radius of curvature, and internal stress state. Then, experimental test methods to determine relevant film properties and analyze the mechanical integrity of flexible devices are detailed. Last, the novel areas of stretchable devices, roll-to-roll processing, and self-repair materials are discussed.

Keywords

Critical strain; Damage mechanics; Fragmentation test; Internal stress; Radius of curvature

1.1. Introduction

The confluence of (soft) organic materials in biology and (hard) inorganic materials in electronics has led during the past several decades to numerous enabling concepts and demonstrations of flexible devices as reviewed by Nathan et al. (2012). Flexible electronics has become a pervasive technology endeavor with a multitude of shape attributes, from single curvature conformal displays and thin film solar cells (Choi, Kim, & Ha, 2008; Crawford, 2005; Lewis, 2006; Pagliaro, Ciriminna, & Palmisano, 2008) to complex curvilinear stretchable devices for biomedical applications (Ko et al., 2009). The extent to which, and the number of times, these multilayer structures can be safely bent or stretched and twisted are essential, but highly challenging design features. In addition to providing basic functions such as electrical conductivity, transparency, or light emission, the selected materials and their structuration into various device architectures must fulfill new criteria to avoid damage during both processing and operational life. Design and process engineers working on the implementation of flexible electronics often lack confidence due to a lack of understanding or a lack of input data for reliable modeling tools. The aim of this Chapter is to introduce basic mechanical concepts and provide key ingredients for rational design of flexible organic electronics. Section 1.2 is devoted to the analysis of stresses and strains and related critical radius of curvature of multilayer structures, with attention paid to relevant material property data and to process-induced internal strains. Section 1.3 and Section 1.4 detail failure mechanics under tensile and compressive loading, respectively, and are illustrated with case studies from the literature. Section 1.5 presents an overview of mechanical test methods available and in development, which are useful to test the limits of multilayer samples and challenge the models described in the two previous sections. Section 1.6 discusses several recent research endeavors relevant to flexible organic electronics including stretchable and foldable devices, roll-to-roll (R2R) processing, and self-repair material strategies. Section 1.7 closes this chapter with a number of final remarks.

1.2. Stress and strain analyses

Figure 1.1 summarizes the main damage events and the state of strain in a compliant substrate coated on both sides with thin brittle films. Upon bending to some radius of curvature, the film located on the convex (top) side experiences tensile strain and may crack and eventually delaminate. The film located on the concave (bottom) side experiences compressive strain and may also delaminate and buckle and possibly crack as well. Also depicted in Figure 1.1 is the through-thickness strain profile. The neutral axis is the plane where the strain does not change upon pure bending. As detailed in the following, the total strain is the sum of an internal strain and a bending strain. The internal strain is essentially controlled by the fabrication process, and is assumed in Figure 1.1 to be compressive in the two films and tensile in the substrate. The bending strain results from the curvature applied during service and is proportional to the distance from the neutral axis.

1.2.1. Critical radius of curvature

The critical radius of curvature, R_crit, is among the key design parameters for flexible electronics. It is defined as the radius of curvature at which device failure occurs because o...

Table of contents

• Cover image
• Title page
• Table of Contents
• Related titles
• Copyright
• List of contributors
• Woodhead Publishing Series in Electronic and Optical Materials
• Part One. Properties and materials
• Part Two. Technologies
• Part Three. Applications
• Index
• Colour section plate captions