Organic Electronics: Devices, Circuits and Applications A DISSERTATION SUBMITTED TO THE DEPARTMENT OF ELECTRICAL ENGINEERING AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Jin Jeon July 2012 © 2012 by Jin Jeon. All Rights Reserved. Re-distributed by Stanford University under license with the author. This work is licensed under a Creative Commons Attribution- Noncommercial 3.0 United States License. http://creativecommons.org/licenses/by-nc/3.0/us/ This dissertation is online at: http://purl.stanford.edu/zv127wb2165 ii I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. Zhenan Bao, Primary Adviser I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. Yoshio Nishi I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. Ada Poon Approved for the Stanford University Committee on Graduate Studies. Patricia J. Gumport, Vice Provost Graduate Education This signature page was generated electronically upon submission of this dissertation in electronic format. An original signed hard copy of the signature page is on file in University Archives. iii ABSTRACT Organic materials have brought exciting opportunities for flexible, light weight, low cost, and disposable electronics. However, there are still several technical challenges for the wide spread of this technology. In this dissertation, I discuss about the challenges and the improvements of organic electronics. In the first part, I explore device engineering for organic thin film transistors (OTFTs). New device architecture and fabrication methods to improve the OTFT characteristics are proposed. Short channel and self-aligned OTFTs are implemented on a non-planer substrate. The self-aligned structure enables accurate alignment between the electrodes with a pre-defined prism-structure dimension, thus reducing parasitic overlap capacitance. In the second part, circuit engineering based on OTFTs is studied. An OTFT circuit design methodology is proposed to enable accurate analysis and verification in the design stage. Various topologies of digital circuits such as complimentary and unipolar OTFT circuits based on this design methodology are demonstrated. The third part focuses on application engineering, specifically on the implementation of disposable and flexible organic electronic sensors. Wireless temperature sensor based on conductive filled polymer is demonstrated. The stability and reproducibility is improved and the sensitive temperature can be tuned by employing a binary polymer system. iv DEDICATION The author wishes to dedicate this dissertation to Eunju Song and Soul Jeon. v ACKNOWLEDGEMENT Foremost, I would like to express my sincere gratitude to my advisor Professor Zhenan Bao for the continuous support of my Ph.D. study and research, for her patience, motivation, enthusiasm, and immense knowledge. Her guidance helped me in all the time of research and writing of this dissertation. I could not have imagined having a better advisor and mentor for my Ph.D. study. I am grateful to Professor Yoshio Nishi and Ada Poon for their precious time and efforts as members of my reading and defense committee. I also thanks to Professor Boris Murmann for his valuable suggestions on my research. I would like to thank all the past and present group members for their great assistance and friendship. Especially, I thank Benjamin T, Dr. Peng Wei, Olasupo (Ade) Johnson, Dr. Do Hwan Kim, Dr. Han-Bo-Ram Lee for the valuable interaction and collaborations. Samsung Mobile Display has been sponsoring me for five years, which was indispensible for my Ph.D. study. Finally, my deepest gratitude goes to my wife, Eunju Song, for her continuous support and inspiration in my life. I also thank to my daughter, my mom and dad. vi TABLE OF CONTENTS Abstract .............................................................................................................................. iv Dedication ............................................................................................................................v Acknowledgement ............................................................................................................. vi Table of Contents .............................................................................................................. vii List of tables .........................................................................................................................x List of figures ..................................................................................................................... xi CHAPTER 1 : Introduction .................................................................................................1 1.1 Organic Semiconductor ...........................................................................................2 1.2 Organic Thin Film Transistor ..................................................................................5 1.2.1 Basic Operation of OTFT ...............................................................................6 1.2.2 Capacitance .....................................................................................................9 1.2.3 Contact Resistance and Device Architectures of OTFT ...............................10 1.2.4 Maximum Operating Frequency ...................................................................14 1.3 Applications ...........................................................................................................15 1.4 Motivation and organization of this dissertation ...................................................17 CHAPTER 2 : Device Engineering ...................................................................................20 2.1 Background and Motivation ..................................................................................20 2.2 A review of channel electrodes patterning methods ..............................................21 2.2.1 Shadow Mask Patterning ..............................................................................21 2.2.2 Photolithography ...........................................................................................23 2.2.3 Nano-Imprinting Lithography (NIL) ............................................................25 2.2.4 Vertical Channel Device Structure ...............................................................26 2.3 A review of self-aligned structures ........................................................................29 2.4 Experimental ..........................................................................................................30 2.5 Fabrication Process of PRISM OTFT ....................................................................31 2.5.1 Fabrication of a Master Mold for Imprinting ................................................32 2.5.2 Imprinting of PRISM Structures ...................................................................34 2.5.3 OTFT Fabrication on Prism Structures .........................................................37 vii 2.6 Characteristics of PRISM OTFT ...........................................................................39 2.6.1 Fabrication Results........................................................................................39 2.6.2 Frequency Characteristic of PRISM OTFTs.................................................40 2.6.3 DC Characteristics of Prism OTFT...............................................................42 2.7 Summary ................................................................................................................43 CHAPTER 3 : Circuit Engineering....................................................................................45 3.1 Background and Motivation ..................................................................................45 3.2 Design Methodology for OTFT Circuits ...............................................................46 3.3 Experimental ..........................................................................................................50 3.4 A Circuit simulation model for OTFT ...................................................................52 3.4.1 The Non-ideal Characteristics of OTFT .......................................................52 3.4.2 Device Model for OTFTs..............................................................................55 3.5 Complementary OTFT Circuits .............................................................................58 3.5.1 Complementary Inverter ...............................................................................58 3.5.2 Electrical Measurement of Complementary Inverter ....................................61 3.6 Unipolar Type Inverter ..........................................................................................63 3.6.1 Conventional Unipolar Circuits ....................................................................64 3.6.2 Bootstrap Unipolar Digital Circuits ..............................................................65 3.6.3 Fabrication of Unipolar Digital Circuits .......................................................69 3.6.4 Electrical Characterizations of Unipolar Digital