Electrohydrodynamic Direct-Writing for Flexible Electronic Manufacturing

Electrohydrodynamic Direct-Writing for Flexible Electronic Manufacturing

Zhouping Yin YongAn Huang Yongqing Duan Haitao Zhang Electrohydrodynamic Direct-Writing for Flexible Electronic Manufacturing 123

Zhouping Yin State Key Laboratory of Digital Manufacturing Equipment Huazhong University of Science Wuhan China YongAn Huang State Key Laboratory of Digital Manufacturing Equipment Huazhong University of Science Wuhan China Yongqing Duan State Key Laboratory of Digital Manufacturing Equipment Huazhong University of Science Wuhan China Haitao Zhang State Key Laboratory of Digital Manufacturing Equipment Huazhong University of Science Wuhan China ISBN 978-981-10-4758-9 ISBN 978-981-10-4759-6 (ebook) https://doi.org/10.1007/978-981-10-4759-6 Library of Congress Control Number: 2017960783 Springer Nature Singapore Pte Ltd. 2018 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Printed on acid-free paper This Springer imprint is published by Springer Nature The registered company is Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Foreword Flexible electronics represent the next-generation microelectronics that offer the electrical functions of conventional, rigid wafer-based technologies but with the ability to be stretched, compressed, twisted, bent, and deformed into arbitrary shapes. They overcome the fundamental mismatch in mechanics and form, and will enable applications that are impossible to achieve with hard, planar integrated circuits. Examples range from surgical and diagnostic implements that naturally integrate with the human body to provide advanced therapeutic capabilities, to sensory skins for robotics, wearable communication devices, to cameras that use biologically inspired designs to achieve superior performance. Fabrication of these flexible electronics is usually based on lithographic patterning and undercut etching, which provides the most well-established routes to high-performance electronics/ optoelectronics. Printing has emerged as an alternative route of fabrication for flexible electronics. The solution-processable electronic materials provide enormous opportunities for the printing techniques for manufacturing of flexible electronics. Inkjet printing, which can deposit electronic materials in a digital, drop-on-demand manner, has become a robust, effective, and powerful technique for electronic manufacturing due to its purely additive operation, compatibility with large-area substrates, and cost-effectiveness. Conventional inkjet printing relies on thermal or piezoelectric actuation and ejection of liquid droplets through nozzle apertures. Its resolution limit is *20 lm, with the range of ink viscosity 5 100 cps, which falls short to fabricate the high-resolution components of electronics (e.g., OTFT and pixel of flexible display) and is inapplicable to highly viscous materials (e.g., polymeric solution and silver paste) widely used in manufacturing of electronics. Electrohydrodynamic (EHD) printing, which adopts electrical field force, rather than thermal bubble pressure or piezoelectric pressure, to pull the fluid flow from the Taylor cone at the nozzle, exhibits the ultra-high resolution (even to the nanoscale) and excellent compatibility with highly viscous inks. It is considered as the next-generation inkjet printing since it can print various functional materials directly onto a large-area v

vi Foreword substrate to form micro-/nanostructures, which is crucial for manufacturing of certain flexible electronics. This book is the first about the EHD printing/direct-writing techniques. It summarizes the groundbreaking research progress in this field, including that of the authors, covering the theoretical and experimental studies on the printability of functional inks, the design and fabrication of nozzles, the development of EHD printer, and the applications in flexible electronics. The electronic solution with viscosity up to 10000 cps, such as silver paste, can be printed to form sub-micrometer structure (about 100 nm) on flexible substrates (PET, metal foil, and glass foil). Major advances have been achieved to accurately control the position and morphology of micro-/nanofibers and to fabricate elaborate micro-/ nanostructures (e.g., the mask for lithography in TFT fabrication and serpentine fibers for ultra-stretchable sensors). The book also covers the Si-based nozzle array of EHD printhead developed by the authors, as well as the EHD printing equipment, which is regarded as a digital lithography machine. These technologies overcome the limitations on the resolution of fabrication and viscosity of ink, and represent major advances in manufacturing of flexible electronics. This book will be of great interest to the scientists and engineers interested in advanced printing techniques and manufacturing of flexible electronics. Yonggang Huang Northwestern University, Evanston, IL, USA

Acknowledgements We are indebted to Dr. Dong Ye, Zhoulong Xu, Yanqiao Pan and Xiaomei Wang, and Ph.D. candidates Yajiang Ding, Jianpeng Liu and Bowen Xu for their support in literature acquisition. We are also immensely grateful to professor Hao Wu for his comments on earlier versions of the manuscript. In addition, we want to express our gratitude to the supports of National Natural Science Foundation of China (No. 51635007, 51605180, and 51035002), and the help of the publisher. vii

Contents 1 Introduction of Electrohydrodynamic Printing... 1 1.1 Background... 1 1.2 EHD Printing... 3 1.2.1 Mechanism and Classification of EHD Printing... 4 1.2.2 EHD Printing System... 6 1.2.3 Development of EHD Direct-Writing... 7 1.2.4 Advantages of EHD Direct-Writing... 11 1.3 Key Technologies for EHD Printing... 11 1.3.1 Printability of Ink... 11 1.3.2 Nozzle... 15 1.3.3 Control Method... 17 1.4 Applications in Flexible Electronics... 18 1.4.1 Printing of Micro/Nano-Structures... 18 1.4.2 Photolithography Mask... 21 1.4.3 Fiber-Based Devices... 23 1.5 Conclusions... 24 References... 26 2 Mechano-electrospinning (MES)... 31 2.1 Introduction... 31 2.2 Modeling and Experiments of MES... 34 2.2.1 Theoretical Model... 35 2.2.2 Comparison Between Experimental and Theoretical Results... 38 2.3 Selection of Process Parameters... 42 2.3.1 Experimental Results... 42 2.3.2 Response Surface Methodology... 44 2.4 Fabrication of Micro-structures... 49 2.4.1 Ribbon-Lattice Structure... 49 2.4.2 Dot Structure... 53 ix

x Contents 2.4.3 Bead-on-String Structure... 57 2.5 Conclusions... 62 References... 62 3 Helix Electrohydrodynamic Printing (HE-Printing)... 67 3.1 Introduction... 67 3.2 Coiling Behavior of the Electrospinning Jet... 69 3.2.1 Coiling Phenomenon... 69 3.2.2 Simulations of the Coiling Behavior... 70 3.2.3 Results and Discussion... 72 3.3 Transformation of Patterns... 75 3.3.1 Experimental Results... 75 3.3.2 Transformation Rules Between Different Patterns... 78 3.4 Applications of HE-Printing... 83 3.4.1 Serpentine Structure... 83 3.4.2 Self-similar Structure... 84 3.5 Conclusions... 87 References... 87 4 Inks for EHD Printing... 89 4.1 Introduction... 89 4.2 Classification of Inks... 91 4.2.1 Inorganic Inks... 91 4.2.2 Organic Inks... 95 4.2.3 Composite Inks... 98 4.3 Evaluation of Printing Performance... 101 4.3.1 Viscosity... 103 4.3.2 Conductivity/Surface Charge Density... 108 4.3.3 Surface Tension... 111 4.4 Conclusions... 112 References... 112 5 Nozzles for EHD Printing... 117 5.1 Introduction... 117 5.1.1 Special Nozzle.... 118 5.1.2 Nozzle Array... 119 5.2 Si-Based Planar Nozzle... 120 5.3 Si-Based Protruding Nozzle... 123 5.4 Multi-level Voltage Method for Addressable Printing... 126 5.5 Conclusions... 130 References... 131 6 Control Method for EHD Printing... 133 6.1 Introduction... 133 6.2 Electrospinning Sedimentary Microstructure Control... 137

Contents xi 6.2.1 Modeling of Sedimentary Microstructure Control... 137 6.2.2 Stability Analysis of the Microstructure Control System... 139 6.3 Fiber Diameter Control of Electrospinning Processes... 144 6.3.1 Modeling of Fiber Diameter Control... 144 6.3.2 Stability Analysis of Fiber Diameter Control System... 148 6.4 Conclusions... 154 References... 155 7 EHD Equipment and Applications... 157 7.1 Introduction of EHD Equipment... 157 7.1.1 Functions... 157 7.1.2 Module Composition... 158 7.2 Stretchable Generator Based on Serpentine Fibers... 167 7.2.1 Experimental Section... 167 7.2.2 Results and Discussion... 168 7.3 Gas Sensor Based on Hierarchical Fibers... 173 7.3.1 Experimental Section... 174 7.3.2 Results and Discussion... 176 7.4 Flexible Small-Channel Thin-Film Transistors... 180 7.4.1 Experimental Section... 181 7.4.2 Results and Discussion... 183 7.5 Conclusions... 190 References... 190