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

The development of transparent p-type oxide semiconductors with good performance may be a true enabler for a variety of applications where transparency, power efficiency, and greater circuit complexity are needed. Such applications include transparent electronics, displays, sensors, photovoltaics, memristors, and electrochromics. Hence, here, recent developments in materials and devices based on p-type oxide semiconductors are reviewed, including ternary Cu-bearing oxides, binary copper oxides, tin monoxide, spinel oxides, and nickel oxides. The crystal and electronic structures of these materials are discussed, along with approaches to enhance valence-band dispersion to reduce effective mass and increase mobility. Strategies to reduce interfacial defects, off-state current, and material instability are suggested. Furthermore, it is shown that promising progress has been made in the performance of various types of devices based on p-type oxides. Several innovative approaches exist to fabricate transparent complementary metal oxide semiconductor (CMOS) devices, including novel device fabrication schemes and utilization of surface chemistry effects, resulting in good inverter gains. However, despite recent developments, p-type oxides still lag in performance behind their n-type counterparts, which have entered volume production in the display market. Recent successes along with the hurdles that stand in the way of commercial success of p-type oxide semiconductors are presented.

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Recent Developments in p-Type Oxide Semiconductor Materials and Devices.

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.

/pdf/metal-oxide-semiconductor-thin-film-transistors-for-flexible-16f7s8g8at.pdf

Metal oxide semiconductor thin-film transistors for flexible electronics

Although paper electronics is a compelling concept, the large surface roughness and opaqueness of most paper substrates has hindered its development from a dormant idea to a thriving technology. A recent demonstration of transparent paper with nanoscale surface roughness has revived an interest in using renewable cellulose substrates for electronics and optoelectronics. In this short review, we will first summarize the recent progress of transparent paper electronics through structure engineering. We will also discuss the properties and functionalization of transparent paper, such as surface roughness, printability, thermal stability, etc. Finally, we will summarize the recent achievements on proof-of-concepts of transparent paper, which pave the way for next-generation green electronics fabricated with roll-to-roll printing methods. Advantages of transparent paper over traditional flexible plastic substrates and its challenges will also be discussed.

Transparent paper: fabrications, properties, and device applications

Solid-state electronics

An amorphous oxide semiconductor thin-film transistor (TFT) with a 47.7-cm2 · V-1 · s-1 field-effect mobility (μFE) and a 1.57-V threshold voltage (VTH) was produced using a double-stacked active layer composed of a 5-nm indium-zinc-oxide layer and a 60-nm gallium-indium-zinc-oxide (GIZO) layer. The μFE is about 2.3 times higher than that of a GIZO TFT, and the VTH is almost same as that of a GIZO TFT. The stability of this TFT with a double-stacked active layer was superior to that of a GIZO TFT.

Improvement of the Performance and Stability of Oxide Semiconductor Thin-Film Transistors Using Double-Stacked Active Layers

By using tin monoxide films, p-channel oxide semiconductor thin film transistors were fabricated with a bottom-gate and bottom-contact structure. A p-type tin monoxide semiconductor thin film was obtained from tin monoxide powder by vacuum thermal evaporation. The as-deposited film showed an amorphous phase, and a polycrystalline tin monoxide was obtained by thermal annealing after the deposition. The hole concentration was on the order of 1017 cm-3, and the Hall mobility was 2.83 cm2 V-1 s-1. The resulting on-current/off-current ratio was more than 102, and the field-effect mobility was approximately 4×10-5 cm2 V-1 s-1.

https://iopscience.iop.org/article/10.1143/JJAP.49.020202/pdf

p-Channel Tin Monoxide Thin Film Transistor Fabricated by Vacuum Thermal Evaporation

High-performance, low-cost amorphous gallium–indium–zinc oxide (a-GIZO) thin-film-transistor (TFT) technology is required for the next generation of active-matrix organic light-emitting diodes. A back-channel-etch structure is the most appropriate device structure for high-performance, low-cost a-GIZO TFT technology. However, channel damage due to source/drain etching and passivation-layer deposition has been a critical issue. To solve this problem, the present work focuses on overall back-channel processes, such as back-channel N2O plasma treatment, SiOx passivation deposition, and final thermal annealing. This work has revealed the dependence of a-GIZO TFT characteristics on the N2O plasma radio-frequency (RF) power and frequency, the SiH4 flow rate in the SiOx deposition process, and the final annealing temperature. On the basis of these results, a high-performance a-GIZO TFT with a field-effect mobility of 35.7 cm2 V–1 s–1, a subthreshold swing of 185 mV dec–1, a switching ratio exceeding 107, and a s...

High-Performance Low-Cost Back-Channel-Etch Amorphous Gallium–Indium–Zinc Oxide Thin-Film Transistors by Curing and Passivation of the Damaged Back Channel

In this study, p-channel amorphous tin oxide thin-film transistors (TFTs) were fabricated. A vacuum thermal evaporation method with an SnO powder source was used to deposit the tin-oxide active layer. Thermal annealing in N 2 and oxygen plasma treatment were used as post-deposition treatments to obtain p-channel switching capabilities from the tin-oxide active layer. We have achieved a field effect mobility of 5.59 cm 2V -1s -1 with these TFTs. With their high mobility and low-cost fabrication process that is applicable to large-sized devices, they represent an advance toward practical oxide semiconductor technology.

Fabrication of p-Channel Amorphous Tin Oxide Thin-Film Transistors Using a Thermal Evaporation Process

Cellulose paper was fabricated and employed as a substrate for flexible organic light-emitting diodes (OLEDs). The performance of the cellulose paper satisfies the criteria for a substrate of an OLED. The visible light transmittance of the cellulose paper was greater than 95% in the visible light wavelength range. After the OLED was fabricated on the cellulose paper substrate through a thermal evaporation method, the OLED exhibited a luminance of 620 cd/m2 at a driving voltage of 15 V and a current efficiency of 0.85 cd/A. This work suggests that cellulose paper is an environmentally promising substrate material for flexible OLEDs.

Ho-Nyeon Lee

Papers

Improvement of the Performance and Stability of Oxide Semiconductor Thin-Film Transistors Using Double-Stacked Active Layers

p-Channel Tin Monoxide Thin Film Transistor Fabricated by Vacuum Thermal Evaporation

High-Performance Low-Cost Back-Channel-Etch Amorphous Gallium–Indium–Zinc Oxide Thin-Film Transistors by Curing and Passivation of the Damaged Back Channel

Fabrication of p-Channel Amorphous Tin Oxide Thin-Film Transistors Using a Thermal Evaporation Process

An OLED Using Cellulose Paper as a Flexible Substrate