Transparent electronics is today one of the most advanced topics for a wide range of device applications. The key components are wide bandgap semiconductors, where oxides of different origins play an important role, not only as passive component but also as active component, similar to what is observed in conventional semiconductors like silicon. Transparent electronics has gained special attention during the last few years and is today established as one of the most promising technologies for leading the next generation of flat panel display due to its excellent electronic performance. In this paper the recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed and p-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed. After a short introduction where the main advantages of these semiconductors are presented, as well as the industry expectations, the beautiful history of TFTs is revisited, including the main landmarks in the last 80 years, finishing by referring to some papers that have played an important role in shaping transparent electronics. Then, an overview is presented of state of the art n-type TFTs processed by physical vapour deposition methods, and finally one of the most exciting, promising, and low cost but powerful technologies is discussed: solution-processed oxide TFTs. Moreover, a more detailed focus analysis will be given concerning p-type oxide TFTs, mainly centred on two of the most promising semiconductor candidates: copper oxide and tin oxide. The most recent data related to the production of complementary metal oxide semiconductor (CMOS) devices based on n- and p-type oxide TFT is also be presented. The last topic of this review is devoted to some emerging applications, finalizing with the main conclusions. Related work that originated at CENIMAT|I3N during the last six years is included in more detail, which has led to the fabrication of high performance n- and p-type oxide transistors as well as the fabrication of CMOS devices with and on paper.

Oxide Semiconductor Thin‐Film Transistors: A Review of Recent Advances

https://iopscience.iop.org/article/10.1088/1468-6996/11/4/044305/pdf

Present status of amorphous In–Ga–Zn–O thin-film transistors

Molybdenum disulfide (MoS(2)) thin-film transistors were fabricated with ion gel gate dielectrics. These thin-film transistors exhibited excellent band transport with a low threshold voltage (<1 V), high mobility (12.5 cm(2)/(V·s)) and a high on/off current ratio (10(5)). Furthermore, the MoS(2) transistors exhibited remarkably high mechanical flexibility, and no degradation in the electrical characteristics was observed when they were significantly bent to a curvature radius of 0.75 mm. The superior electrical performance and excellent pliability of MoS(2) films make them suitable for use in large-area flexible electronics.

Highly flexible MoS2 thin-film transistors with ion gel dielectrics.

Amorphous oxide semiconductors (AOSs) are expected as new channel materials in thin-film transistors (TFTs) for large-area and/or flexible flat-panel displays and other giant-microelectronics devices. So far, many prototype displays have been demonstrated in these four years since the first report of AOS TFT. The most prominent feature of AOS TFTs is that they operate with good performances even if they are fabricated at low temperatures without a defect passivation treatment. The TFT mobilities exceed 10 cm2/(Vmiddots), which are more than ten times larger than those of conventional amorphous semiconductor devices. In addition, they operate at low voltages, e.g., < 5 V owing to their small subthreshold voltage swings. These features indicate that electron transport in oxide semiconductors are insensitive to random structures and these oxides do not form high-density defects that affect electron transport and TFT operation. In this paper, we discuss the origins of the prominent features of AOS devices from the viewpoint of materials science of AOS.

Origins of High Mobility and Low Operation Voltage of Amorphous Oxide TFTs: Electronic Structure, Electron Transport, Defects and Doping

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

We demonstrated flexible amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) on fully transparent and high-temperature polyimide-based nanocomposite substrates. The flexible nanocomposite substrates were coated on the carrier glass substrates and were debonded after the TFT microfabrication. The adoption of the Ti/IZO stacked electrodes as source/drain/ gain electrodes significantly improved the etching compatibility with other material layers, enabling successful implementation of flexible a-IGZO TFTs onto the transparent nanocomposite substrates by conventional lithographic and etching processes. The flexible a-IGZO TFTs exhibited decent mobility and mechanical bending capability. Field-effect mobility of up to 15.9 cm2/V · s, a subthreshold swing of 0.4 V/dec, a threshold voltage of 0.8 V, and an on/off ratio of >; 108 were extracted from the TFT characteristics. The devices could be bent down to a radius of curvature of 3 mm and yet remained normally functional. Such successful demonstration of flexible oxide TFTs on transparent flexible substrates using fully lithographic and etching processes that are compatible with existing TFT fabrication technologies shall broaden their uses in flexible displays and electronics.

High-Performance Flexible a-IGZO TFTs Adopting Stacked Electrodes and Transparent Polyimide-Based Nanocomposite Substrates

Self-aligned techniques are often used in conventional CMOS and Si-based thin-film transistors (TFTs) technologies due to various merits. In this paper, we report self-aligned coplanar top-gate InGaZnO TFTs using PECVD a-SiNinfin:H patterned to have low hydrogen content in the channel region and high hydrogen content in the source/drain region. After annealing to induce hydrogen diffusion from a-SiNinfin:H into the oxide semiconductor, the source-drain regions become more conductive and yet the channel region remains suitable for TFT operation, yielding a working self-aligned TFT structure. Such fabrication involves neither back-side exposure nor ion implantation, and thus may be compatible with the typical and cost-effective TFT manufacturing.

Self-Aligned Top-Gate Coplanar In-Ga-Zn-O Thin-Film Transistors

We report the successful implementation of top-gate staggered amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) with decent performance and environmental stability by adopting the SiOx/SiNx bilayer gate-insulator stack. The PECVD SiOx and SiNx were used as the first and second gate insulators, respectively, in the TFT to simultaneously ensure the channel/gate-insulator interface properties for device performances and the water impermeability of the gate insulator for effective passivation of the channel layer. It was also found that the cleanliness of the back-channel interface (and thus the effectiveness of the source/drain etching process) is critical for the successful implementation of the top-gate staggered a-IGZO TFTs. In this paper, a two-step wet-etching process for source/drain was used to ensure the quality of the back-channel interface. Finally, we successfully integrated the top-gate staggered a-IGZO TFTs into a working 2.2-in active matrix organic light-emitting display panel, demonstrating the real use of the developed TFTs.

Top-Gate Staggered a-IGZO TFTs Adopting the Bilayer Gate Insulator for Driving AMOLED

A process was developed for fine fabrication of amorphous IGZO TFTs and integrated circuits on flexible and colorless polyimide substrates TFTs with field-effect mobilities of ∼10 cm2/Vs and ring oscillators with propagation delay of 035 μs per stage were achieved on the polyimide substrates

/pdf/p-11-amorphous-in2o3-ga2o3-zno-thin-film-transistors-and-ct6nk4jbfb.pdf

P‐11: Amorphous In2O3‐Ga2O3‐ZnO Thin Film Transistors and Integrated Circuits on Flexible and Colorless Polyimide Substrates

— Amorphous-oxide-semiconductor thin-film transistors (TFTs) have gained wide attention in recent years due to their many merits. In this paper, a series of top-gate transparent thin-film transistors (TFTs) based on amorphous-indium—gallium—zinc—oxide (a-IGZO) semiconductors have been fabricated and investigated. Specifically, low-temperature SiNx and SiOx were used as the gate insulator and different Ar/O2 gas-flow ratios were used for a-IGZO channel deposition to study the influences of gate insulators and channel-deposition conditions. In addition to the investigation of device performance, the stability of these TFTs was also examined by applying constant-current stressing. It was found that a high mobility of 30-45 cm2/V-sec and small threshold-voltage shift in constant-current stressing can be achieved using SiNx with suitable hydrogen-content stoichiometry as the gate insulator and the carefully adjusted Ar/O2 flow ratio for channel deposition. These results may be associated with hydrogen incorporation into the channel, the lower defect trap density, and the better water/oxygen barrier properties (impermeability) of the low-temperature SiNx.

Cheng-Han Wu

Papers

High-Performance Flexible a-IGZO TFTs Adopting Stacked Electrodes and Transparent Polyimide-Based Nanocomposite Substrates

Self-Aligned Top-Gate Coplanar In-Ga-Zn-O Thin-Film Transistors

Top-Gate Staggered a-IGZO TFTs Adopting the Bilayer Gate Insulator for Driving AMOLED

P‐11: Amorphous In2O3‐Ga2O3‐ZnO Thin Film Transistors and Integrated Circuits on Flexible and Colorless Polyimide Substrates

Influence of channel‐deposition conditions and gate insulators on performance and stability of top‐gate IGZO transparent thin‐film transistors