Printed Electronics E-Book

Zheng Cui

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 706

Veröffentlichungsjahr: 2016

Beschreibung

This book provides an overview of the newly emerged and highly interdisciplinary field of printed electronics * Provides an overview of the latest developments and research results in the field of printed electronics * Topics addressed include: organic printable electronic materials, inorganic printable electronic materials, printing processes and equipments for electronic manufacturing, printable transistors, printable photovoltaic devices, printable lighting and display, encapsulation and packaging of printed electronic devices, and applications of printed electronics * Discusses the principles of the above topics, with support of examples and graphic illustrations * Serves both as an advanced introductory to the topic and as an aid for professional development into the new field * Includes end of chapter references and links to further reading

Leseprobe

PRINTED ELECTRONICS

MATERIALS, TECHNOLOGIES AND APPLICATIONS

Zheng Cui

Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO),Chinese Academy of Sciences, China

With contributions from

Chunshan ZhouSong QiuZheng ChenJian LinJianwen ZhaoChangqi MaWenming Su

Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO),Chinese Academy of Sciences, China

This edition first published 2016

© 2016 Higher Education Press. All rights reserved.

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Library of Congress Cataloging-in-Publication data applied for

ISBN: 9781118920923

Preface

My involvement in printed electronics started in 2009 when I returned to China, after 20 years of working in the UK. My previous career was centered around the development and application of microfabrication and nanofabrication technologies. Going back to China gave me the opportunity to do something different. I joined the Suzhou Institute of Nano-Tech and Nano-Bionics, which is one of the research institutes within the Chinese Academy of Sciences, and set up the Printable Electronics Research Center (PERC) there with the help of start-up funds from the Institute and from the Administration of Suzhou Industrial Park where the Institute is located. Six years ago, printed electronics was quite a new field, particularly in China. The PERC that I set up was then the first research center dedicated to printed electronics R&D in China. Although I started on printed electronics from scratch, my previous years of experience on micro-nanofabrication helped me to understand printed electronics from the manufacturing perspective, which is different from those with a background in materials science. Printing is, after all, an additive fabrication similar to lithography-based micro-nanofabrication.

Over the last six years, PERC has built up a multidisciplinary research team and well-equipped laboratories. We decided to develop the technology from all directions, including synthesis and formulation of electronic inks, development of printing processes, printable thin-film transistors, photovoltaic, and organic light emission. We have even worked on encapsulation technology for organic electronic devices which are known to be susceptible to water and oxygen. The ultimate goal of PERC is to develop those technologies that could be useful and practical, eventually leading to some products that the market needs. With our efforts, we have achieved a great deal in the last six years. We developed a range of electronic inks from inorganic materials such as carbon nanotubes, metal oxides, copper and aluminum, and dielectrics, to organic photovoltaic and organic light-emitting materials. We developed a range of printing processes including inkjet printing, aerosol jet printing, gravure printing, gravure offset printing and screen printing. We succeeded in making thin-film transistors on flexible substrates using inorganic inks, making gravure and inkjet-printed organic solar cells, and making flexible organic light emitting diodes, as well as barrier films for encapsulation of organic devices. An innovative hybrid printing technique we developed has been implemented by industry to realize mass production of transparent conductive films for touch panels. We are very proud of what we have achieved in this new and exciting field.

When we started working on printed electronics, we were very much aware that the field was not only new to us but also new to the majority of other scientists and engineers. This was particularly the case in China. We felt from very early on that more people should know about printed electronics and more researchers should get involved in the development, which is the only way to push the technology forward. So we began to plan a book. With the diligent work of my team, the Chinese book, Printed Electronics: Materials, Technologies and Applications, was published by the Chinese Higher Education Press in March 2012. This was the first book on printed electronics ever published in China. Three years have passed since this book was published. On the one hand, technology has moved on with new advances in the last three years. On the other hand, the authors of the first Chinese book have gained more experience by working directly in the field. It was time to update the book and we decided to write an English version to share the knowledge and information about printed electronics not only with readers in China but also with readers around the world. This English book is not simply a translation of the previously published Chinese book, but has newly updated information including some of our own work carried out at PERC in the past three years.

This book is written with members of my own research team, which is a multidisciplinary team with diverse backgrounds from physics to chemistry and to electronic engineering. Dr. Chunshan Zhou (author of Chapter 2 – the Chinese version of this chapter was written by Dr. Song Qiu who used to work at PERC) is an organic chemist at PERC working on organic semiconductor materials synthesis; Dr. Zheng Chen (author of Chapter 3) is leading the research at PERC on inorganic nanomaterials for electronic inks and printable inorganic thin-film transistors; Dr. Jian Lin (author of Chapter 4) is the expert on printing processes at PERC; Dr. Jianwen Zhao (author of Chapter 5) has been working on printed carbon nanotubes thin-film transistors since he was a postdoctoral researcher in Singapore six years ago. He has developed a range of techniques to purify and formulate single-walled semiconductor carbon nanotube inks and successfully printed high performance thin-film transistors; Dr. Changqi Ma (author of Chapter 6) is the leader of the organic photovoltaic group at PERC. With organic chemistry training during his Ph.D studies and a number of years of working in Germany, he has developed some new organic photovoltaic materials and is recently working on perovskite solar cells; Dr. Wenming Su (author of Chapters 7 and 8) is the expert on organic light-emitting diodes (OLED) and thin-film encapsulation at PERC, and is leading the engineering group at PERC. Since the authors themselves are directly practicing in their relevant topic area, they are well qualified to write on the topics. We put into the book not only the information and knowledge published by others, but also our own research experience and results. As the leader of PERC and the organizer of this book, I myself contributed Chapters 1 and 9, which reflect my understanding of printed electronics and my observation of the technological progress in the last six years with my deep involvement in the field. I also took charge of the English editing of all chapters.

There are already books published on organic electronics and flexible electronics. Printing as an alternative manufacturing technology gives organic electronics and flexible electronics extra dimensions and new application possibilities. We tried not to have too much overlap with organic electronics and flexible electronics. We organized the information we gathered specifically on printing and printed aspects of making electronics with or without organic materials and with or without flexible substrates. Printed electronics is still a growing field. The technology is still in its early stage of development. We hope that we have put together a comprehensive set of information and knowledge so that readers of the book will gain a general understanding of printed electronics, the materials and technologies that are involved in this field and the potential applications. The contents have been organized and presented in a logical way so that people with a general knowledge of physics, chemistry and electronics will be able to comprehend. We hope that this book will serve as a guide for anyone who is interested in printed electronics and that useful information may be found in the book. Due to the limitations of our own experience and knowledge, there may inevitably be errors and inaccuracy of information in this book; we sincerely welcome comments and criticisms on the book from experts in the field.

Finally, I would like to give my sincere thanks to my team members at the Printable Electronics Research Center (PERC), Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO), Chinese Academy of Sciences (CAS). This book is truly the fruit of team effort. My acknowledgement also goes to the funding bodies that have provided major financial supports to my research team in the last five years under the National Key Basic Research Program of China (2015CB351900), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA01020304) and the National Natural Science Foundation of China (91123034).

Zheng Cui

1Introduction

Zheng Cui

1.1 What is Printed Electronics?

Printed electronics, as the name implies, is a type of electronics that are created by printing technology. To be more specific, it is an electronic science and technology based on conventional printing techniques as the means to manufacture electronics devices and systems. To most people, “printed electronics” is an unfamiliar phrase. Even experts in electronics may not have heard it. Many people may have it confused with conventional printing technology or mixed up with electronic printing. Conventional printing is for printing paper media, such as books, newspapers, and magazines. Even electronic printing is not printed electronics. Electronic printing is still conventional media printing but with more use of computers and electronic typesetting. A closer analogy to printed electronics would be electronics or integrated circuit (IC)-based electronics, rather than conventional printing. The aim of printed electronics is to make integrated electronic systems using printing technology instead of much more expensive and complex IC manufacturing technology.

Silicon-based IC technology has been in use for nearly 60 years. Modern silicon microelectronics and its manufacturing technology have evolved into an extremely complicated process. There are several hundreds of steps involved in producing a silicon IC chip, from the preparation of single crystal silicon substrates to making billions of transistors and getting these transistors interconnected, including repeated thin film deposition, lithography, etching, and packaging [1]. IC manufacturing has become so expensive that the latest deep UV photolithography system can cost tens of millions of dollars, whereas an extreme UV lithography system for making silicon chips at below 32 nm feature size has a price tag of more than $120 million [2]. The IC industry has become so investment intensive that only a handful companies in the world can afford to play in the field. On the other hand, printing is a very simple process compared to the IC manufacturing process, as illustrated in Figure 1.1 In order to turn a functional material into a functional structure or pattern on a silicon substrate, IC manufacturing has to go through thin film deposition, spin-coating photoresist layer, baking, photolithography, baking, developing, etching, and stripping of the photoresist masking layer. If printing is employed, the functional material can be directly printed as patterns onto the substrate. Only a subsequent annealing/sintering process is needed.

Figure 1.1 Comparison of IC manufacturing and printing processes. (a) Conventional IC manufacturing; and (b) printing process

Printing is an additive manufacturing process, similar to the deposition process in micro- and nanofabrication [3] but combined with patterning. In printed electronics, the components of an electronic device or a system can be made by printing in additive fashion. For example, for a field-effect transistor, the source, drain, and gate electrodes, as well as semiconductor and insulating layers, can all be printed in ink forms and layer by layer onto a substrate. It is very much like color printing in a conventional printing press, where each color ink is printed sequentially and several color layers are overlaid to form the final color print. Because of its similarity to the printing process, the machine to print electronics is not much different from a conventional media printer. Figure 1.2 compares a conventional roll-to-roll paper media printer and an electronics printer. They look almost the same. The only difference is the inks they use. The inks for printing electronics have conducting, semiconducting, or dielectric properties. They are electronic materials, not pigment, which is the key for printing to be used for printed electronics.

Figure 1.2 Comparison of (a) conventional paper media printer; and (b) electronics printer.

(Courtesy of iPEN Co. Ltd.)

Printed electronics originated from organic electronics. In 1977, Alan Heeger, together with Alan G. MacDiarmid and Hideki Shirakawa, discovered that polymer could be conductive by doping certain molecules [4], which earned them the Nobel Prize in Chemistry in 2000. This discovery completely overthrew the conventional wisdom that organic polymer materials are always insulators. Following the discovery of conductive polymers, organic semiconductor materials were developed in 1983 [5] and organic field-effect transistors (OFETs) were first made in 1986 [6]. In the same period, Dr. C.W. Tang at Kodak developed organic photovoltaic (OPV) materials [7] and later invented the organic light-emitting diode (OLED) [8], from which organic electronics as a field of scientific interest started.

The reason the scientific community got interested in organic electronics was not only due to scientific curiosity but more importantly that they foresaw the prospect of printing electronic devices from organic polymers that could be naturally made into ink forms. Once they could be printed, electronic devices could be made on a massive scale at low cost, very much like printing newspapers. So from the early stage of development, people made attempts to process organic electronic materials in solution forms to make transistors [9]. In 1994, a research group led by Francis Garnier first reported OFETs made on plastic substrates [10]. Although only electrodes were printed and the organic semiconductors were deposited by vacuum evaporation, the significance of the work was that it proved transistors could be made on plastic substrates, opening the era of plastic electronics. Fully printed transistors were reported in 1997 when Dr. Zhenan Bao, working at Bell Labs, printed all layers including conductor, semiconductor, and dielectrics onto polyester (PET) film by a screen printing technique [11]. More recently, Professor Sirringhaus at Cambridge University made fully printed organic transistors by the inject printing technique [12].

It is apparent that organic electronics had its eye on low cost printing electronics from the beginning of its development. However, for a very long period, printing did not become the mainstream fabrication means for making organic electronic devices. The main reason lies in the fact that the charge mobility, which is a key property of semiconductor material, for the solution form of organic semiconductors is always lower than those small molecular organic semiconductors that cannot be made into solution form and have to be deposited by vacuum evaporation. In other words, transistors made by printable organic materials are not as good as those made by vacuum evaporated organic materials.

Charge mobility is the speed of electronic charge (electrons for n-type semiconductor or holes for p-type semiconductor) movement in semiconductor materials. It determines how fast a transistor switches at an applied external electric field. Table 1.1 lists the charge mobility of commonly used inorganic semiconductor materials, in comparison with organic semiconductor. It shows that the charge mobility of organic semiconductor materials is far lower than inorganic semiconductors.

Table 1.1 Charge mobility of organic and inorganic semiconductor materials

Semiconductor materials

Charge mobility (cm

2

v

−1

s

−1

)

GaAs

10

4

Single-crystal silicon

10

3

Poly silicon

10

Amorphous silicon

 0.1–1

Organic semiconductor

10

−4

–1

The research in organic electronics in its over 3 decades of development history has been mainly focused on how to improve the charge mobility, as it is obvious that only high mobility organic semiconductors have value in any practical applications. The last 25 years have indeed seen the steady improvement of charge mobility in organic semiconductors, as shown in Figure 1.3, which indicates the evolution of charge mobility from 1985 to 2010 for three different types of organic p-channel and n-channel semiconductor materials: vacuum-deposited small molecular organic materials, solution-processed small molecular organic materials, and solution-processed polymer materials [13].

Figure 1.3 Evolution of charge mobility for organic semiconductor materials.

(Adapted from [13] with permission from the Royal Society of Chemistry.)