Flexible Glass: Enabling Thin, Lightweight, and Flexible Electronics
This new compilation by authors from a range of companies and institutions will be a useful resource for practicing engineers, engineering students, and others with an interest in flexible glass and electronics.
by Ioannis Kymissis
Flexible Glass: Enabling Thin, Lightweight, and Flexible Electronics presents a compelling argument that flexible glass has arrived. Ultrathin glass is now available from a variety of suppliers, and this volume, featuring contributions by a variety of experts and edited by Sean M. Garner of Corning, builds the case that the material has extraordinary performance, with the best optical properties of any flexible substrate, excellent thermal properties, and infinite barrier protection against water vapor and oxygen. The authors also discuss the equally important availability of a range of unit operations for high-throughput handling, coating, and treating of flexible glass, which allows for the development of new electronic and optical systems that take advantage of the material’s unique properties.
In the first of the book’s three major sections, Corning-affiliated authors discuss the fabrication of flexible glass, its mechanical and barrier properties, and its formulation. They describe the mechanics behind ultrathin glass’s flexibility as well as how the fusion-draw process enables the formation of perfect sheets of ultrathin glass that allow for a reasonable radius of curvature without breaking. One chapter provides a review of fracture mechanics, the mechanical testing of glass sheets, and the longevity of glass. Another describes the significant improvement that can be made to the durability of glass sheets when formulated for a reduced modulus. This is an emerging area in flexible glass.
The other two sections of the book are by authors who are not affiliated with Corning. The first discusses the unit operations available for glass processing and coating. The authors, from the Center for Advanced Microelectronics Manufacturing in Binghamton, New York, demonstrate roll-to-roll deposition, photolithographic patterning, and wet-processing tools in a roll format for the development of several new structures. The deposition and patterning of indium tin oxide (ITO) films are also showcased. The authors compare the performance of flexible glass head to head with two other high-performance flexible films for roll-to-roll coating operations, polyethylene naphthalate (PEN) and polyethylene terephthalate (PET), and demonstrate that the barrier properties and surface quality of flexible glass offer significant performance improvements.
A chapter by authors from the Fraunhofer Institute for Organic Electronics in Dresden discusses plasma processing associated with roll-to-roll and sheet-fed flexible electronics processing, as well as the considerations associated with roll-to-roll atomic layer deposition processing. Of particular interest is the applicability of flexible glass to more energetic processes (such as ion beam-assisted deposition), which offer higher-quality and more stable films than traditional processes but are challenging to incorporate in process flows using polymer substrates. The authors also discuss the use of heating and ultrafast annealing (e.g., with flashlamps or excimer lasers) for the improvement of film characteristics. In another chapter, authors affiliated with VTT Finland present results for solution-based printing on flexible glass, making a compelling case for the applicability of flexible glass to printing. They cite mechanical properties (e.g., mating with gravure rollers), surface cleanliness, and surface cleaning and treatment options as evidence that flexible glass is an exceptional choice.
The third and final section of Flexible Glass describes several applications of the technology. Authors affiliated with the US National Renewable Energy Laboratory in Golden, Colorado, discuss the applicability of flexible glass to photovoltaics. The demands of photovoltaic devices for transparency, UV stability, weatherization tolerance, and water exclusion are very high, and the applicability of flexible glass as a substrate or laminate is considered in this context. A group from the University of Stuttgart discusses the use of flexible glass in displays, including stress management, the fabrication of thin-film transistors (TFTs), and the integration of drive electronics. Researchers from the University of Pittsburgh discuss the use of flexible glass as a component in integrated waveguides, presenting several new processes for structuring, cladding, and patterning. The final chapter, from mPower Technology and Vivint Solar, lays out the potential use of flexible glass as a substrate for the integration of heterogeneous elements in a 3D integrated circuit (3DIC), including electronics, photovoltaics, and sensor devices. The authors show a demonstrator that incorporates a high-voltage photovoltaic cell and discuss the potential cost scaling for such a platform.
A Healthy Range of Concepts and Authors
I was especially impressed by the diversity of voices in this book. While Corning is the only glass supplier among the contributors, the rest of the authors hail from a variety of institutions around the world and include many of the top practitioners and institutions involved in flexible electronics research. Each chapter is well referenced and reviews literature by the authors as well as by other experts as appropriate for the section.
This book does a good job of mixing a review of fundamentals into the discussion of new technologies and concepts. In addition to an unusually comprehensive and clear discussion of the mechanics of flex and fracture (which by itself would make an interesting book), the authors were not shy about discussing a number of other interesting and related topics, starting at a foundational level. For example, the review of ITO doping and the tradeoff of ITO doping with oxygen vacancies and transparency is particularly helpful. Additional educational sections include a review of optical properties such as haze, an explanation of water-vapor transmission requirements for thin-film electronics, and a discussion of the sheet resistance of transparent conductors. This coverage expands the accessibility of the book to students and engineers from outside the field who may not be well versed in issues specific to flexible electronics, and bolsters the work’s usefulness as a guide to many of the issues associated with flexible electronics beyond the topics relating to flexible glass.
In this context, I think Flexible Glass is a good resource for institutional libraries and the personal libraries of those interested in flexible electronics (and new substrates), while also serving as a textbook for specialized courses, and as an update on issues relating to flexible electronics. It has the fundamentals needed to serve as an excellent textbook in several related topics, and features enough recent and cutting-edge results to provide an update to those interested in considering flexible glass specifically and flexible electronics generally. It is also available on Knovel, which means that it’s already in many institutional libraries. Overall, this is a highly recommended reference and a great read covering the field.
Flexible Glass: Enabling Thin, Lightweight, and Flexible Electronics is edited by Sean M. Garner and published by Scrivener Publications and Wiley, 2018.
Ioannis Kymissis is an associate professor in the electrical engineering department at Columbia University and former editor in chief of the
Journal of the Society for Information Display. •