Metal oxide semiconductor thin-film transistors for flexible electronics

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

Design and simulation of a smart bottle with fill-level sensing based on oxide TFT technology

Packaging is an important element responsible for brand growth and one of the main rea-sons for producers to gain competitive advantages through technological innovation. In this re-gard, the aim of this work is to design a fully autonomous electronic system for a smart bottle packaging, being integrated in a European project named ROLL-OUT. The desired application for the smart bottle is to act as a fill-level sensor system in order to determine the liquid content level that exists inside an opaque bottle, so the consumer can exactly know the remaining quantity of the product inside. An in-house amorphous indium–gallium–zinc oxide thin-film transistor (a-IGZO TFT) model, previously developed, was used for circuit designing purposes. This model was based in an artificial neural network (ANN) equivalent circuit approach. Taking into account that only n-type oxide TFTs were used, plenty of electronic building-blocks have been designed: clock generator, non-overlapping phase generator, a capacitance-to-voltage converter and a comparator. As it was demonstrated by electrical simulations, it has been achieved good functionality for each block, having a final system with a power dissipation of 2.3 mW (VDD=10 V) not considering the clock generator. Four printed circuit boards (PCBs) have been also designed in order to help in the testing phase. Mask layouts were already designed and are currently in fabrication, foreseeing a suc-cessful circuit fabrication, and a major step towards the design and integration of complex trans-ducer systems using oxide TFTs technology

Low-temperature amorphous oxide semiconductors for thin-film transistors and memristors: physical insights and applications

While amorphous oxides semiconductors (AOS), namely InGaZnO (IGZO), have found market application in the display industry, their disruptive properties permit to envisage for more advanced concepts such as System-on-Panel (SoP) in which AOS devices could be used for addressing (and readout) of sensors and displays, for communication, and even for memory as oxide memristors are candidates for the next-generation memories. This work concerns the application of AOS for these applications considering the low thermal budgets (< 180 °C) required for flexible, low cost and alternative substrates. For maintaining low driving voltages, a sputtered multicomponent/multi-layered high-κ dielectric (Ta2O5+SiO2) was developed for low temperature IGZO TFTs which permitted high performance without sacrificing reliability and stability. Devices’ performance under temperature was investigated and the bias and temperature dependent mobility was modelled and included in TCAD simulation. Even for IGZO compositions yielding very high thermal activation, circuit topologies for counteracting both this and the bias stress effect were suggested. Channel length scaling of the devices was investigated, showing that operation for radio frequency identification (RFID) can be achieved without significant performance deterioration from short channel effects, which are attenuated by the high-κ dielectric, as is shown in TCAD simulation. The applicability of these devices in SoP is then exemplified by suggesting a large area flexible radiation sensing system with on-chip clock-generation, sensor matrix addressing and signal read-out, performed by the IGZO TFTs. Application for paper electronics was also shown, in which TCAD simulation was used to investigate on the unconventional floating gate structure. AOS memristors are also presented, with two distinct operation modes that could be envisaged for data storage or for synaptic applications. Employing typical TFT methodologies and materials, these are ease to integrate in oxide SoP architectures

Technological Integration in Printed Electronics

Conventional electronics requires the use of numerous deposition techniques (e.g. chemical vapor deposition, physical vapor deposition, and photolithography) with demanding conditions like ultra-high vacuum, elevated temperature and clean room facilities. In the last decades, printed electronics (PE) has proved the use of standard printing techniques to develop electronic devices with new features such as, large area fabrication, mechanical flexibility, environmental friendliness and—potentially—cost effectiveness. This kind of devices is especially interesting for the popular concept of the Internet of Things (IoT), in which the number of employed electronic devices increases massively. Because of this trend, the cost and environmental impact are gradually becoming a substantial issue. One of the main technological barriers to overcome for PE to be a real competitor in this context, however, is the integration of these non-conventional techniques between each other and the embedding of these devices in standard electronics. This chapter summarizes the advances made in this direction, focusing on the use of different techniques in one process flow and the integration of printed electronics with conventional systems

Materials, Device, and System Integration of Amorphous Oxide Semiconductor TFTs

Amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) have great potential for use in the next-generation of electronics. AOS TFTs can be used to fabricate circuits and sensors on various substrates, due to unique properties, including high mobility, excellent uniformity, and it requiring a low-temperature process. Currently, indium gallium zinc oxide (IGZO) is the predominant AOS used in the display industry as a TFT semiconductor. Although the IGZO technology is very mature, the development of AOS continues. Additional AOSs are being investigated to reduce cost and improve stability. Considering availability and the potential of materials, indium silicon oxide (ISO) was selected for this project. ISO uses silicon to suppress the instability originating from the oxygen vacancy. The silicon-oxygen bond has a higher dissociation energy, which improves retention of oxygen atoms in the film, and thus, increases the transistor’s stability. This detailed study follows a bottom-up approach. It starts with the fabrication and characterisation of materials. Basic material properties of the ISO film are discussed within, including amorphicity, bandgap, stoichiometry, and Hall-effect parameters. Based on the characterisation results, different deposition recipes for the TFT were developed and tested. The interface quality and etching selectivity were investigated. Uniformity and stability data were extracted from a TFT array using the developed photo-lithography process, which was used to verify and quantitate the capability of the process in system integration and circuit design. A Monte-Carlo simulation environment was established based on the extracted data. The two urgent challenges in all-TFT analogue circuit design, the lack of proper active load and the large parasitic capacitance, were investigated. In-depth analysis on these two issues and applicable solutions were presented. Investigation on system integration of TFT circuits and sensors were conducted, since the device demonstrated the required performance and uniformity. An all-TFT differential-input amplifier was designed and verified, as the first mixed signal all-TFT circuit.China Scholarship Council Cambridge Trus