The field of flexible electronics has rapidly expanded over the last decades, pioneering novel applications, such as wearable and textile integrated devices, seamless and embedded patch-like systems, soft electronic skins, as well as imperceptible and transient implants. The possibility to revolutionize our daily life with such disruptive appliances has fueled the quest for electronic devices which yield good electrical and mechanical performance and are at the same time light-weight, transparent, conformable, stretchable, and even biodegradable. Flexible metal oxide semiconductor thin-film transistors (TFTs) can fulfill all these requirements and are therefore considered the most promising technology for tomorrow's electronics. This review reflects the establishment of flexible metal oxide semiconductor TFTs, from the development of single devices, large-area circuits, up to entirely integrated systems. First, an introduction on metal oxide semiconductor TFTs is given, where the history of the field is revisited, the TFT configurations and operating principles are presented, and the main issues and technological challenges faced in the area are analyzed. Then, the recent advances achieved for flexible n-type metal oxide semiconductor TFTs manufactured by physical vapor deposition methods and solution-processing techniques are summarized. In particular, the ability of flexible metal oxide semiconductor TFTs to combine low temperature fabrication, high carrier mobility, large frequency operation, extreme mechanical bendability, together with transparency, conformability, stretchability, and water dissolubility is shown. Afterward, a detailed analysis of the most promising metal oxide semiconducting materials developed to realize the state-of-the-art flexible p-type TFTs is given. Next, the recent progresses obtained for flexible metal oxide semiconductor-based electronic circuits, realized with both unipolar and complementary technology, are reported. In particular, the realization of large-area digital circuitry like flexible near field communication tags and analog integrated circuits such as bendable operational amplifiers is presented. The last topic of this review is devoted for emerging flexible electronic systems, from foldable displays, power transmission elements to integrated systems for large-area sensing and data storage and transmission. Finally, the conclusions are drawn and an outlook over the field with a prediction for the future is provided.

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Metal oxide semiconductor thin-film transistors for flexible electronics

Recent advances in flexible and stretchable electronics (FSE), a technology diverging from the conventional rigid silicon technology, have stimulated fundamental scientific and technological research efforts. FSE aims at enabling disruptive applications such as flexible displays, wearable sensors, printed RFID tags on packaging, electronics on skin/organs, and Internet-of-things as well as possibly reducing the cost of electronic device fabrication. Thus, the key materials components of electronics, the semiconductor, the dielectric, and the conductor as well as the passive (substrate, planarization, passivation, and encapsulation layers) must exhibit electrical performance and mechanical properties compatible with FSE components and products. In this review, we summarize and analyze recent advances in materials concepts as well as in thin-film fabrication techniques for high-k (or high-capacitance) gate dielectrics when integrated with FSE-compatible semiconductors such as organics, metal oxides, quantum...

High- k Gate Dielectrics for Emerging Flexible and Stretchable Electronics

High-mobility two-dimensional (2D) semiconductors are desirable for high-performance mechanically flexible nanoelectronics. In this work, we report the first flexible black phosphorus (BP) field-effect transistors (FETs) with electron and hole mobilities superior to what has been previously achieved with other more studied flexible layered semiconducting transistors such as MoS2 and WSe2. Encapsulated bottom-gated BP ambipolar FETs on flexible polyimide afforded maximum carrier mobility of about 310 cm2/V·s with field-effect current modulation exceeding 3 orders of magnitude. The device ambipolar functionality and high-mobility were employed to realize essential circuits of electronic systems for flexible technology including ambipolar digital inverter, frequency doubler, and analog amplifiers featuring voltage gain higher than other reported layered semiconductor flexible amplifiers. In addition, we demonstrate the first flexible BP amplitude-modulated (AM) demodulator, an active stage useful for radio r...

Flexible black phosphorus ambipolar transistors, circuits and AM demodulator

Advances in the synthesis and scalable manufacturing of single-walled carbon nanotubes (SWCNTs) remain critical to realizing many important commercial applications. Here we review recent breakthroughs in the synthesis of SWCNTs and highlight key ongoing research areas and challenges. A few key applications that capitalize on the properties of SWCNTs are also reviewed with respect to the recent synthesis breakthroughs and ways in which synthesis science can enable advances in these applications. While the primary focus of this review is on the science framework of SWCNT growth, we draw connections to mechanisms underlying the synthesis of other 1D and 2D materials such as boron nitride nanotubes and graphene.

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Carbon Nanotubes and Related Nanomaterials: Critical Advances and Challenges for Synthesis toward Mainstream Commercial Applications

The nitrides of most of the group IVb-Vb-VIb transition metals (TiN, ZrN, HfN, VN, NbN, TaN, MoN, WN) constitute the unique category of conductive ceramics. Having substantial electronic conductivity, exceptionally high melting points and covering a wide range of work function values, they were considered for a variety of electronic applications, which include diffusion barriers in metallizations of integrated circuits, Ohmic contacts on compound semiconductors, and thin film resistors, since early eighties. Among them, TiN and ZrN are recently emerging as significant candidates for plasmonic applications. So the possible plasmonic activity of the rest of transition metal nitrides (TMN) emerges as an important open question. In this work, we exhaustively review the experimental and computational (mostly ab initio) works in the literature dealing with the optical properties and electronic structure of TMN spanning over three decades of time and employing all the available growth techniques. We critically evaluate the optical properties of all TMN and we model their predicted plasmonic response. Hence, we provide a solid understanding of the intrinsic (e.g. the valence electron configuration of the constituent metal) and extrinsic (e.g. point defects and microstructure) factors that dictate the plasmonic performance. Based on the reported optical spectra, we evaluate the quality factors for surface plasmon polariton and localized surface plasmon for various TMN and critically compare them to each other. We demonstrate that, indeed TiN and ZrN along with HfN are the most well-performing plasmonic materials in the visible range, while VN and NbN may be viable alternatives for plasmonic devices in the blue, violet and near UV ranges, albeit in expense of increased electronic loss. Furthermore, we consider the alloyed ternary TMN and by critical evaluation and comparison of the reported experimental and computational works, we identify the emerging optimal tunable plasmonic conductors among the immense number of alloying combinations.

Conductive nitrides: Growth principles, optical and electronic properties, and their perspectives in photonics and plasmonics

This letter demonstrates the feasibility of full room temperature InGaZnO thin-film transistor (TFT) using trilayer gate dielectric on flexible substrate Through integrating high-κ SiO2/TiO2/SiO2 (STS) gate-stack as well as InGaZnO channel thickness modulation, the resulting flexible indium-gallium-zinc oxide (IGZO)/STS TFTs show low threshold voltage of 05 V, small subthreshold swing of 0129 V/decade, high field effect mobility of 76 cm2/Vs , and good ION/IOFF ratio of 67×105, which have the potential for the application of high-resolution flexible display

https://ir.nctu.edu.tw:443/bitstream/11536/21854/1/000319460800017.pdf

A Flexible IGZO Thin-Film Transistor With Stacked ${\rm TiO}_{2}$ -Based Dielectrics Fabricated at Room Temperature

We report a high performance indium-gallium-zinc oxide (IGZO)/IGZO:Ti bilayer metal-oxide thin-film transistor (TFT) with a low drive voltage of . Compared with conventional IGZO TFTs, the novel bilayer metal-oxide TFTs through IGZO thickness modulation can reach the lowest off current of 1.6×10-11 A, smallest sub-threshold swing of 73 mV/decade, and highest mobility of 63 cm2/Vs, which may create the potential application for high resolution display.

https://ir.nctu.edu.tw:443/bitstream/11536/23385/1/000329061300029.pdf

High Mobility Bilayer Metal–Oxide Thin Film Transistors Using Titanium-Doped InGaZnO

In this work, we report a one-transistor (1T) versatile memory; the memory transistor characteristics achieve sub-60-mV/dec operation and considerably low off-state leakage of 10−15 A/µm at a supply voltage below 0.5V. The versatile memory features DRAM/NVM functions of large ΔV T window of 2.8V, fast 20-ns speed, 103s retention at 85°C, and long extrapolated 1016 endurance at 85°C, which show the potential for 3D memory application with severe requirement on both high density and low power consumption.

Low power 1T DRAM/NVM versatile memory featuring steep sub-60-mV/decade operation, fast 20-ns speed, and robust 85°C-extrapolated 10 16 endurance

Abstract Transparent electronics has attracted much attention and been widely studied for next-generation high-performance flat-panel display application in the past few years, because of its excellent electrical properties. In display application, thin film transistors (TFTs) play an important role as the basic units by controlling the pixels. Among them, oxide-based TFTs have become promising candidates and gradually replaced the conventional amorphous and polycrystalline silicon TFTs, due to high mobility, good transparency, excellent uniformity and low processing temperature. Even though n-type oxide TFTs have shown high device performance and been used in commercial display application, p-type oxide TFTs with the equal performance have been rarely reported. Hence, in this paper, recent progress and challenges in p-type oxide-based TFTs are reviewed. After a short introduction, the TFT device structure and operation are presented. Then, recent developments in p-type oxide TFTs are discussed in detail, with the emphasis on the potential p-type oxide candidates as copper oxide, tin oxide and nickel oxide. Moreover, miscellaneous applications of p-type oxide TFTs are also presented. Despite this, the performance of p-type oxide TFTs still lags behind, as compared with that of n-type counterparts. Thus, the current issues and challenges of p-type oxide TFTs are briefly discussed.

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Progress and challenges in p-type oxide-based thin film transistors

This study demonstrates the feasibility of producing an InGaZnO thin-film transistor (TFT) using a high-κ germanium oxide (GeO 2 )/titanium oxide (TiO 2 )/GeO 2 gate stack on a flexible polycarbonate substrate. The flexible TFT exhibited a small sub-threshold swing of 0.132 V/decade, an acceptable field effect mobility of 8 cm 2 /(V s), and a robust I on /I off ratio of 2.4 × 10 7 . The improved device performance can be attributed to the combined effect of high- κ TiO 2 and the large band gap of GeO 2 that exhibits a tendency to remain in a Ge 4+ oxidation state at room temperature.

https://ir.nctu.edu.tw:443/bitstream/11536/23294/1/000327291800031.pdf

Hsiao-Hsuan Hsu

Papers

A Flexible IGZO Thin-Film Transistor With Stacked ${\rm TiO}_{2}$ -Based Dielectrics Fabricated at Room Temperature

High Mobility Bilayer Metal–Oxide Thin Film Transistors Using Titanium-Doped InGaZnO

Low power 1T DRAM/NVM versatile memory featuring steep sub-60-mV/decade operation, fast 20-ns speed, and robust 85°C-extrapolated 10 16 endurance

Progress and challenges in p-type oxide-based thin film transistors

Fully room-temperature IGZO thin film transistors adopting stacked gate dielectrics on flexible polycarbonate substrate