Flexible Electronics: From Materials To Devices

From Materials to Devices

Guozhen Shen, Zhiyong Fan

• Publisher: WSPC
• Year: 2016
• eBook ISBN: 9789814656009
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

"Overall, the work is written at a level suitable for any individual with a reasonable familiarity of device physics and materials science. It will be useful to advanced undergraduate students who show an interest in the field. Also, this work will serve as a strong reference for those graduate students or researchers who are new to the discipline of flexible electronics."

CHOICE Connect
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This book provides a comprehensive overview of the recent development of flexible electronics. This is a fast evolving research field and tremendous progress has been made in the past decade. In this book, new material development and novel flexible device, circuit design, fabrication and characterizations will be introduced. Particularly, recent progress of nanomaterials, including carbon nanotubes, graphene, semiconductor nanowires, nanofibers, for flexible electronic applications, assembly of nanomaterials for large scale device and circuitry, flexible energy devices, such as solar cells and batteries, etc, will be introduced. And through reviewing these cutting edge research, the readers will be able to see the key advantages and challenges of flexible electronics both from material and device perspectives, as well as identify future directions of the field.

--> Contents:

• Carbon Nanotube Flexible Electronics (Chuan Wang)
• Nanomaterial-Based Flexible Sensors (Kuniharu Takei)
• Graphene: From Synthesis to Applications in Flexible Electronics (Henry Medina, Wen-Chun Yen, Yu-Ze Chen, Teng-Yu, Yu-Chuan Shih and Yu-Lun Chueh)
• Integrating Semiconductor Nanowires for High Performance Flexible Electronic Circuits (Ning Han and Johnny C Ho)
• Graphene Devices for High-Frequency Electronics and THz Technology (Guangcun Shan, Ruguang Ma, Xinghai Zhao and Wei Huang)
• Design of Nanostructures for Flexible Energy Conversion and Storage (Zhuoran Wang, Di Chen and Guozhen Shen)
• Next Generation Flexible Solar Cells (Wei Chen, Wenjun Zhang, Huan Wang and Xianwei Zeng)
• Flexible Solar Cells (Dongdong Li, Dongliang Yu, Zhiyong Fan, Linfeng Lu and Xiaoyuan Chen)
• Recent Advances in Fiber Supercapacitors (Lingxia Wu, Jinping Liu and Yuanyuan Li)
• Flexible Electronic Devices Based on Electrospun Micro-/Nanofibers (Bin Sun, Miao Yu, Yun-Ze Long and Wen-Peng Han)

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Readership: Academics, researcher and graduate students in electrical & electronic engineering, microelectronics and nanomaterials & nanostructures.
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CHAPTER 1

CARBON NANOTUBE FLEXIBLE ELECTRONICS

Chuan Wang

Department of Electrical and Computer Engineering,
Michigan State University
428 S. Shaw Lane, Engineering Building #2120,
East Lansing, Michigan, USA
[email protected]

Single-wall carbon nanotubes (SWNTs) possess fascinating electrical properties and offer new entries into a wide range of novel electronic applications that are unattainable with conventional Si-based devices. The field initially focused on the use of individual or parallel arrays of nanotubes as the channel material for ultrascaled nanoelectronic devices. However, the challenge in the deterministic assembly of SWNTs has proven to be a major technological barrier. In recent years, solution deposition of semiconductor-enriched SWNT networks has been actively explored for high performance and uniform thin-film transistors (TFTs) on both mechanically rigid and flexible substrates. This presents a unique niche for nanotube electronics by overcoming their limitations and taking full advantage of their superb electronic properties. This chapter focuses on the large-area processing and electronic properties of SWNT TFTs. A wide range of applications in flexible electronics including integrated circuits, radio-frequency (RF) transistors, displays, and electronic skins will be discussed. With emphasis on large-area systems where nm-scale accuracy in the assembly of nanotubes is not required, the demonstrations show SWNTs’ immense promise as a low-cost and scalable TFT technology for flexible electronic systems with excellent device performances.

1.Introduction

Single-wall carbon nanotubes (SWNTs) can be considered as monolayer graphene sheets with a honeycomb structure that are rolled into seamless, hollow cylinders. Owing to their small size (diameter around 1–2 nm), as well as their superior electronic properties without surface dangling bonds, SWNTs hold great potential for a wide range of applications in solid-state devices and are envisioned as one of the promising candidates for beyond-silicon electronics. SWNTs can be categorized by their chiral vectors defined on the hexagonal crystal lattice using two integers (m and n). The chiral vectors correspond to the direction along which a graphene sheet is wrapped to result in a SWNT. The electronic properties of SWNTs heavily depend on their chiral vectors and the SWNTs can be either metallic (m = n or m − n is a multiple of 3) or semiconducting (all other cases).^1–4 Using this rule of thumb, one can infer from the possible (n,m) values that one third of SWNTs are metallic and the other two thirds are semiconducting. For practical use as the active channel component of electronic devices, semiconducting SWNTs are commonly used. The advantages of semiconducting SWNTs over other conventional semiconductors are multifold. First of all, the charge carriers in carbon nanotubes have long, mean free paths, on the order of a few hundred nanometers for acoustic phonon scattering mechanism. As a result, scattering-free ballistic transport of carriers at low electric fields can be achieved in carbon nanotubes at moderate channel lengths (e.g., sub-100 nm).⁵ Second, the carrier mobility of semiconducting nanotubes is experimentally measured to be > 10,000 cm²V⁻¹s⁻¹,^6,7 at room temperature which is higher than the state-of-the-art silicon transistors. Finally, their small diameters enable excellent electrostatics with efficient gate control of the channel for highly miniaturized devices. Thereby, SWNTs have stimulated enormous interest in both fundamental research and practical applications in nano- and macro-electronics.

Researchers have previously demonstrated excellent field-effect transistors (FETs)^5–12 and integrated circuits^13–17 using individual SWNTs. Figures 1(a) and 1(b) depict the transfer (I_DS–V_GS) and output (I_DS–V_DS) characteristics of the state-of-the-art individual SWNT-FET with self-aligned source/drain contacts and near ballistic transport.¹¹ Impressive performance with subthreshold slope (SS) of 110 mV/dec, on-state conductance of 0.5 × 4e²/h and saturation current upto 25 μA/tube (diameter ~1.7 nm) has been achieved in devices with channel lengths down to 50 nm.¹¹ Better SS of ~70 mV/dec, which is close to the theoretical limit of 60 mV/dec, has also been achieved in transistors with slightly longer channel lengths (500 nm).¹⁰ More recently, SWNT-FETs with sub –10 nm channel lengths have been demonstrated.¹² Such devices exhibit an impressive SS of 94 mV/dec, current on/off ratio of 10⁴, and on-current density of 2.41 mA/μm, which outperform silicon FETs with comparable channel length. Using SWNT-FETs, integrated circuits with various functionalities have been demonstrated. Notable examples include a five-stage ring oscillator (Fig. 1(c)) and pass-transistor-logic-based integrated circuits (full adder, multiplexer, decoder, D-latch, etc.).^16,17

Figure 1. State-of-the-art individual SWNT transistors and circuits. (a) I_DS−V_GS characteristics of a self-aligned ballistic SWNT-FET with a channel length of 50 nm. Inset: Scanning Electron Microscope (SEM) image of the device. (b) Experimental (solid line) and simulated (open circle) I_DS–V_DS characteristics of the same device shown in panel (a). Inset: schematic of the device. Reproduced with permission from Ref. 11. (Copyright 2004 American Chemical Society.) (c) SEM image of a 5-stage ring oscillator constructed on an individual SWNT. Reproduced with permission from Ref. 16. (Copyright 2006 The American Association for the Advancement of Science (AAAS).)

Despite the tremendous progress made with individual nanotube transistors and circuits, major technological challenges remain, including the need for deterministic assembly of nanotubes on a handling substrate with nm-scale accuracy, minimal device-to-device performance variation, and development of a fabrication process scalable and compatible with industry standards. Hence, the use of carbon nanotubes for nanoelectronic applications is still long from being realized. On the other hand, the use of SWNT networks, especially based on semiconductor-enriched samples, present a highly promising path for the realization of high performance thin-film transistors (TFTs) for macro- and flexible electronic applications. The most significant advantages of using SWNT random networks for TFTs lie in the fact that the SWNT thin-films are mechanically flexible, optically transparent, and can be prepared using solution-based room temperature processing, all of which cannot be provided by amorphous and poly silicon technologies.^18–20 Compared with organic semiconductors,^21–25 the other competing platform for flexible TFTs, the SWNT thin-films offer significantly better carrier mobility (~2 orders of magnitude improvement). Thereby, large-area TFT applications seem to offer an ideal niche for carbon nanotube based electronics, taking advantage of their superb physical, chemical and electrical properties without being hindered from their precise assembly limitations down to nm-scale.

Numerous research efforts have been devoted to the successful realization of large-scale chemical vapor deposition (CVD) growth of highdensity horizontally aligned SWNTs on single crystal quartz or sapphire substrates.^26–34 Transfer techniques have been further developed, enabling the demonstration of high-performance transistors and integrated circuits using the aligned nanotubes on various types of rigid and flexible substrates.^35–42 However, considering the fact that roughly one third of the as-grown nanotubes are metallic, techniques such as electrical break-down⁴³ is necessary to remove the leakage-causing metallic paths, which adds complexity, is not scalable, and significantly degrades the device performance due to the high applied fields during the process. Preferential growth of aligned semiconducting SWNTs has been reported recently,^32,44,45 which is an important step forward, however, the purity is not yet high enough to achieve transistors with high on/off current ratio (I_on/I_off) for digital applications. Therefore, for the purpose of obtaining devices with better I_on/I_off, it is more attractive to have networks of SWNTs with higher percentage of sem...

Table of contents

• Cover
• Halftitle
• Title
• Copyright
• Contents
• Chapter 1 Carbon Nanotube Flexible Electronics
• Chapter 2 Nanomaterial-Based Flexible Sensors
• Chapter 3 Graphene: From Synthesis to Applications in Flexible Electronics
• Chapter 4 Integrating Semiconductor Nanowires for High Performance Flexible Electronic Circuits
• Chapter 5 Graphene Devices for High-Frequency Electronics and THz Technology
• Chapter 6 Design of Nanostructures for Flexible Energy Conversion and Storage
• Chapter 7 Next Generation Flexible Solar Cells
• Chapter 8 Flexible Solar Cells
• Chapter 9 Recent Advances in Fiber Supercapacitors
• Chapter 10 Flexible Electronic Devices Based on Electrospun Micro-/Nanofibers
• Index