Printed Electronics Technology Research Articles

Towards truly sustainable IoT systems: the SUPERIOT project

This paper provides an overview of the SUPERIOT project, an EU SNS JU (Smart Networks and Services Joint Undertaking) initiative focused on developing truly sustainable IoT systems. The SUPERIOT concept is based on a unique holistic approach to sustainability, proactively developing sustainable solutions considering the design, implementation, usage and disposal/reuse stages. The concept exploits radio and optical technologies to provide dual-mode wireless connectivity and dual-mode energy harvesting as well as dual-mode IoT node positioning. The implementation of the IoT nodes or devices will maximize the use of sustainable printed electronics technologies, including printed components, conductive inks and substrates. The paper describes the SUPERIOT concept, covering the key technical approaches to be used, promising scenarios and applications, project goals and demonstrators which will be developed to the proof-of-concept stage. In addition, the paper briefly discusses some important visions on how this technology may be further developed in the future.

Printed Electronics Technologies for Additive Manufacturing of Hybrid Electronic Sensor Systems

Printed Electronics Technologies for Additive Manufacturing of Hybrid Electronic Sensor Systems

Printed Electronics in Radiofrequency Energy Harvesters and Wireless Power Transfer Rectennas for IoT Applications

AbstractThe Internet of Things is currently one of the fastest‐growing branches in electronics. The development of energy storage systems and the miniaturization of dedicated printed circuit boards significantly influence that growth. However, the need for batteries and traditional printed circuit boards still limits devices' minimum size, weight, and cost, narrowing the application area. Energy harvesters and wireless power transfer systems fabricated with printed electronics can significantly reduce such devices' weight, size, and cost. Printed electronics technology provides scalable tools for many electronics applications, shortening the validation time and enabling new low‐cost or disposable solutions on lightweight and flexible substrates embedded inside 3D printed structures and directly on device housings. Energy harvesting and wireless power transfer systems in electronic devices can provide enough power to minimize battery capacity and size or even eliminate the need for batteries in low‐power applications. This review presents an adaptation of printed electronics technology in the fabrication of radio frequency energy harvesters and wireless power transfer rectennas for IoT applications. Last, perspectives for development towards greater integration with microsystems, transient electronics with ecofriendly materials, adaptation for next‐generation telecommunication systems, and 3D structural electronics solutions are briefly discussed.

Crack Detecting Method Based on Grid-Type Sensing Networks Using Electrical Signals.

Cracks have a primary effect on the failure of a structure. Therefore, the development of crack sensors with high accuracy and resolution and cracks detection method are important. In this study, the crack sensors were fabricated, and the crack locations were detected with the electrical signal of the crack sensor. First, a metal grid-type micro-crack sensor based on silver was fabricated. The sensor is made with electrohydrodynamics (EHD) inkjet printing technology, which is well known as the next generation of printed electronics technology. Optimal printing conditions were established through experiments, and a grid sensor was obtained. After that, single cracks and multiple cracks were simulated on the sensor, and electrical signals generated from the sensor were measured. The measured electrical signal tracked the location of the cracks in three steps: simple cross-calculation, interpolation, and modified P-SPICE. It was confirmed that cracks could be effectively found and displayed using the method presented in this paper.

Preparation of paper-based conductive pattern for 3D printing

With the development of printed electronics technology, the demand for printed conductive inks had also put forward higher standards. The shortcomings of traditional printed circuit boards, such as complex technology, consumables, and pollution, had also been resolved with the development of 3D printing technology. In this paper, low-content silver nanoparticles were blended with graphene alcohol slurry and dissolved in a non-polluting solvent such as absolute ethanol. The synergistic effect of the composite of the hexagonal structure of the graphene sheet and the silver nanoparticles improved the ink’s performance of electrical conductivity, adding water-based polyurethane/acrylic resin system to improve the adhesion between ink and paper. The conductive ink can be used to 3D print circuit circuits on paper. After drying, the resistance was measured. After the battery, diode, and switch were connected, a circuit diagram was made. After pressing the diode emits was lighted. This work is expected to be applied to flexible circuit boards to provide basic research.

Printed Electronics Technologies for Additive Manufacturing of Hybrid Electronic Sensor Systems

AbstractRequirements for the miniaturization of electronics are constantly increasing as more and more functions are aimed to be integrated into a single device. At the same time, there are strong demands for low‐cost manufacturing, environmental compatibility, rapid prototyping, and small‐scale productions due to fierce competition, policies, rapid technical progress, and short innovation times. Altogether, those challenges cannot be sufficiently addressed by simply using either printed or silicon electronics. Instead, the synergies from combining those two technologies into so‐called hybrid electronics create novel opportunities for advanced capabilities and new areas of applications. In the first part of this review, printing and patterning technologies are presented with potential compatibility with conventional electronics manufacturing techniques. They can be utilized for the fabrication of highly complex structures. Nonetheless, up‐scalability, integration, and adaptation for industrial fabrication remain challenging due to technically limiting factors. Consequently, a special focus is placed on the up‐scalability, availability of commercial printing, and manufacturing machines, as well as processing challenges for high‐volume industrial applications. The second part of this review further provides an overview of exciting and innovative application possibilities of printed electronics, emphasizing sensor applications, as well as additively manufactured integrated circuits.

Inkjet printing of silver conductive ink on textiles for electronic applications: impact of ink formulation on electrical performances of the ink

Printed electronics technology is one of the most dynamic in the world, allowing for the low-cost fabrication of electronic networks on textile substrates using the inkjet printing technique which is commonly used in various industries. In the field of formulation of conductive inks, silver nanoparticles are generally used as precursors that confer electrical conductivity to the printed patterns. In the present work, we synthesized silver nanoparticles by an ecological reduction method and then dispersed them in a PEG/Glycerol mixture to prepare a conductive ink. The silver nanoparticles were characterized by X-ray diffraction (XRD), as well as the morphology of the printed silver tracks was characterized by SEM. The developed ink was then successfully printed on a piece of pre-treated cotton fabric to produce flexible electronic components on the textile.

Low-Cost Direct-Writing of Silver-Based Ink for Planar Microwave Circuits up to 10 GHz

Direct ink writing (DIW) of conductive ink is a printed electronics technology that allows a variety of electronic circuits to be produced in a simple way and with minimal waste of materials. In recent years it has been used for rapid prototyping of RF circuits typically working at S-band frequencies (2–4 GHz). In an attempt to extend this frequency range while maintaining cost-effective prototyping, this work has focused on proving the feasibility of DIW of silver-conductive (SC) ink for the fabrication of planar microwave circuits beyond 10 GHz, more specifically, ultra-wideband (UWB) antennas for medical applications. For this purpose, the DC and RF performance of the SC ink, as well as the FR4 substrate used, were first evaluated. Based on the comparison between experimental and simulated results, we have found that the effective RF conductivity of the SC ink is approximately 27.6% of its DC value and 3.4% of the copper conductivity. A few test microstrip circuits were fabricated by DIW, namely two S-band filters and one UWB antenna. The overall measured performance of all of them agreed well with simulations. In particular, the DIW antenna exhibited a bandwidth of 8.2 GHz (between 2.4 and 10.6 GHz), and was compared with an identical copper antenna showing that both have very similar characteristics. It was also found that the lower conductivity of SC ink as compared to copper led to a gain reduction of only 0.3 dB.

Speed and Scalability of Ambipolar Deep-Subthreshold TFTs for Ultralow-Power Printed Electronics

This work evaluates the speed and scalability potential of ambipolar deep-subthreshold printed-carbon-nanotube thin-film transistors (CNT-TFTs) for the design of ultra-low-power CMOS-like circuits. Transistor and circuit simulations are developed based on experimental device measurements. Our simulations allow the assessment of this emerging printed electronics technology in terms of speed, energy/power consumption and scalability to digital circuits of progressively higher transistor count including elementary logic gates, ring-oscillators and other representative digital circuits. It is shown that digital circuits based on this technology are compatible with propagation delays ≤ 1 ms per NOT logic gate, while operating at ultra-low supply voltages (0.2 V) and with ultra-low static power dissipation (1 pW). Finally, this study develops Monte Carlo simulations to assess the impact of device parameter variations on the viability of large-scale circuit integration based on ambipolar deep-subthreshold printed-CNT-TFTs.

Nickel oxide-based flexible thin-film NTC thermistors by using reverse offset printing

In recent years, the use of printing methods to fabricate electronic devices (printed electronics) has attracted attention because of their low cost and low environmental impact. Printing technology enables the high-throughput fabrication of electrical circuits on film substrates, thereby providing inexpensive personal healthcare devices to monitor health status in real-time, for example. Temperature detection is one of the central concerns as a fundamental physical quantity in various fields. In 2013, a highly sensitive flexible thermistor was reported by formulating aqueous inks of nickel oxide (NiO) nanoparticles for inkjet printing. However, it required a high-temperature calcination process of more than 200 °C, which led to the use of expensive polyimide films with high heat resistance. It is necessary to promote further the development of low-temperature processes for printed thermistors to realize flexible negative temperature coefficient (NTC) thermistors at low cost using printed electronics technology. Moreover, in screen printing and inkjet printing, the definition of the ink pattern applied on the substrate changes due to spreading and coffee distortion phenomena, and the thickness between sensors becomes non-uniform, which is a structural consistency problem that can lead to variations in sensing performance. Therefore, in this study we developed low-temperature processable printed NTC thermistors with a temperature-sensitive layer of NiO by using reverse offset printing. The NTC thermistors were fabricated by printing a comb-like pattern of silver nanoparticles and a thin NiO film. In addition, the low-temperature formation of a NiO layer by oxygen plasma treatment was investigated, and x-ray photoelectron spectroscopy was used to carry out compositional analysis of the surface. Together with the plasma-assisted calcination, a flexible NTC thermistor formed on polyethylene terephthalate film is demonstrated.

Light-Based IoT: Developing a Full-Duplex Energy Autonomous IoT Node Using Printed Electronics Technology.

The light-based Internet of things (LIoT) concept defines nodes that exploit light to (a) power up their operation by harvesting light energy and (b) provide full-duplex wireless connectivity. In this paper, we explore the LIoT concept by designing, implementing, and evaluating the communication and energy harvesting performance of a LIoT node. The use of components based on printed electronics (PE) technology is adopted in the implementation, supporting the vision of future fully printed LIoT nodes. In fact, we envision that as PE technology develops, energy-autonomous LIoT nodes will be entirely printed, resulting in cost-efficient, flexible and highly sustainable connectivity solutions that can be attached to the surface of virtually any object. However, the use of PE technology poses additional challenges to the task, as the performance of these components is typically considerably poorer than that of conventional components. In the study, printed photovoltaic cells, printed OLEDs (organic light-emitting diodes) as well as printed displays are used in the node implementation. The dual-mode operation of the proposed LIoT node is demonstrated, and its communication performance in downlink and uplink directions is evaluated. In addition, the energy harvesting system’s behaviour is studied and evaluated under different illumination scenarios and based on the results, a novel self-operating limitation aware algorithm for LIoT nodes is proposed.

Photo-Sintered Silver Thin Films by a High-Power UV-LED Module for Flexible Electronic Applications.

In recent printed electronics technology, a photo-sintering technique using intense pulsed light (IPL) source has attracted attention, instead of conventional a thermal sintering process with long time and high temperature. The key principle of the photo-sintering process is the selective heating of a thin film with large light absorption coefficients, while a transparent substrate does not heat by the IPL source. Most research on photo-sintering has used a xenon flash lamp as a light source. However, the xenon flash lamp requires instantaneous high power and is unsuitable for large area applications. In this work, we developed a new photo-sintering system using a high-power ultraviolet light emitting diode (UV-LED) module. A LED light source has many merits such as low power consumption and potential large-scale application. The silver nanoparticles ink was inkjet-printed on a polyethylene terephthalate (PET) and photo-sintered by the UV-LED module with the wavelength of 365 and 385 nm. The electrical resistivity as low as 5.44 × 10−6 Ω·cm (just about three times compared to value of bulk silver) was achieved at optimized photo-sintering conditions (wavelength of 365 nm and light intensity of 300 mW/cm2).

Failure Mechanisms in Flip‐Chip Bonding on Stretchable Printed Electronics

Accelerating progress in printed electronics technology transforms the future of the manufacturing process in industrial applications, consumer electronics, and healthcare products. However, real‐life applications demand for circuits and systems that are robust and can stay functional under strong and frequent mechanical deformations. Herein, both empirical and analytical approaches to gain insight on the reliability of ultrathin bare dies on soft and highly stretchable printed circuits are used. To this end, a set of conductive ink and adhesive variants are used to develop a stretchable wireless temperature logger as the test device. The electromechanical performance of the conductive inks is first verified through the screening tests and the most suitable candidates are selected to use with different anisotropic conductive adhesives (ACAs) for chip bonding process. The performance of the test devices (per ink–adhesive combination) is tested through cyclic elongation of 60 samples to provide statistical results. Different failure modes are visualized through cross‐sectional images using broad ion beam (BIB) milling and scanning electron microscopy (SEM). The findings, herein, recognize pad delamination, air voids at the chip‐to‐substrate interface, stiffness of the conductive adhesives, and bonding parameters (pressure and temperature) as the key contributors to the contact failures in the chip assembly.

Single and dual-gate organic field-effect transistors based on diketopyrrolopyrrole-diethienothiophene polymers: performance modulation via dielectric interfaces

Low-power, flexible, and properly encapsulated integrated circuits are the basic requirements of the solution-processed printed and wearable electronic prototypes for various emerging applications including display circuits, sensors, and radio-frequency identification tags. The organic field-effect transistor is one of the important types of devices used in such prototypes and its industrial applicability is essential for the printed electronics technology. The performance deterioration upon encapsulated through the thick layer of air-stable dielectric material such as amorphous fluoropolymer [CYTOP] - must be compensated by device engineering. In this work, we used furan and thiophene flanked diketopyrrolopyrrole donor-acceptor conjugated polymers namely PDPPF-DTT and PDPPT-DTT, and its comparative study was performed using Cytop as a dielectric material. The work advances interface engineering towards the single-gate and dual-gate organic transistors. Dual-gate transistors performance modulation using Cytop dielectric opens new research avenues towards stability enhancement of such transistors for real-world applications.

Inkjet Printing of Flexible Transparent Conductive Films with Silver Nanowires Ink.

The inkjet printing process is a promising electronic printing technique for large-scale, printed, flexible and stretchable electronics because of features such as its high manufacturing speed, environmental friendliness, simple process, low cost, accurate positioning, and so on. As the base material of printed conductive patterns, conductive ink is the foundation of the development of printed electronics technology, and directly affects the performance and the quality of electronic products. In this paper, conductive ink with silver nanowires (AgNWs) was prepared, with AgNWs of lengths of 2–5 µm and diameters of 20 nm or so, isopropyl alcohol and ethylene glycol as the mixed solvents, and modified polysilane as the wetting agent. We discussed the relationship between the formula of the AgNWs ink and the surface tension, viscosity, contact angle between ink droplet and poly(ethylene) terephthalate (PET) surface, as well as the film-forming properties of the ink. Further, we analyzed the effects of the number of printed layers and the ink concentration of the AgNWs on the microstructures, photoelectric properties and accuracy of the printed patterns, as well as the change in the sheet resistance of the film during different bending cycles. The experimental results show that flexible transparent conductive patterns with a light transmittance of 550 nm of 83.1–88.4% and a sheet resistance of 34.0 Ω∙sq−1–78.3 nm∙sq−1 can be obtained by using AgNWs ink of 0.38 mg∙mL−1 to 0.57 mg∙mL−1, a poly (ethylene terephthalate) (PET) substrate temperature of 40 °C, a nozzle temperature of 35 °C, and heat treated at 60 °C for 10 min. These performances indicate the excellent potential of the inkjet printing of AgNWs networks for developing flexible transparent conductive film.

Development of a flexible dielectric-barrier-discharge plasma actuator fabricated by inkjet printing using silver nanoparticles-based ink

We demonstrate that a flexible dielectric-barrier-discharge (DBD) plasma actuator fabricated by an inkjet printing process using metallic inks generates stable surface discharge and ionic wind for active airflow control. The establishment of a practical fabrication method for DBD plasma actuators is a critical issue to be tackled for industrial applications. The inkjet process requires just the printing of the metallic inks and sintering processes while the conventional photolithography technology requires a lot of processes for the fabrication of the DBD plasma actuators. The electrical and mechanical characteristics of a multi-stage DBD plasma actuator fabricated by this printed electronics technology are investigated and are compared with the DBD plasma actuator made by the conventional method using copper tape. The DBD plasma actuator developed in this study induces a similar or even stronger ionic wind than that of the conventional one. Also, a thin exposed electrode (≃1 μm), which is preferable in terms of airflow control applications, is achieved by the inkjet printing process. The development of the fabrication method using printed electronics expands the application field of the DBD plasma actuator, including complex curved surfaces and full-scale size applications.

Development of soft actuator made of polyimide film using printed electronics technology

Development of soft actuator made of polyimide film using printed electronics technology

Printed Sensor Technologies for Monitoring Applications in Smart Farming: A Review

Smart farming is the integration of advanced technologies such as sensors, wireless communication, Internet of Things (IoT), artificial intelligence (AI), and robots, with traditional farming practices. The goal is to increase the yield and quality of the crops or other agricultural products, as well as to reduce the cost and improve efficiency. Sensors play a critical role in smart farming as they provide the most important information related to varied aspects of agriculture, namely soil conditions, plant growth, and environmental conditions. With the emergence of printed electronics technologies, printed sensors have gained much attention in recent years. Printed sensors are fabricated through the additive manufacturing and are extremely versatile. They can be made on any solid substrate and be conformable, flexible, stretchable, low-cost, and/or bio-degradable. These unique features have made the printed sensors attractive for a variety of applications. This article aims to review the potential applications of printed sensors in smart farming. First, the state of the art of printed sensor fabrication is presented with a discussion on their advantages and disadvantages. Then, the measurement and monitoring applications of printed sensors in the key aspects of smart farming, are reviewed, including measurement of chemicals, soil monitoring, and microclimate monitoring in greenhouses. The article also pinpoints the limitations and potentials of printed sensors for farming applications. This article will benefit the researchers and practitioners in the field to advance the printed sensor technologies to mitigate the current issues in smart farming.

Hybrid low-voltage physical unclonable function based on inkjet-printed metal-oxide transistors

Modern society is striving for digital connectivity that demands information security. As an emerging technology, printed electronics is a key enabler for novel device types with free form factors, customizability, and the potential for large-area fabrication while being seamlessly integrated into our everyday environment. At present, information security is mainly based on software algorithms that use pseudo random numbers. In this regard, hardware-intrinsic security primitives, such as physical unclonable functions, are very promising to provide inherent security features comparable to biometrical data. Device-specific, random intrinsic variations are exploited to generate unique secure identifiers. Here, we introduce a hybrid physical unclonable function, combining silicon and printed electronics technologies, based on metal oxide thin film devices. Our system exploits the inherent randomness of printed materials due to surface roughness, film morphology and the resulting electrical characteristics. The security primitive provides high intrinsic variation, is non-volatile, scalable and exhibits nearly ideal uniqueness.

인쇄전자 패턴의 핀홀 측정 방법 개발

In printed electronics technology, the pinholes in the printed pattern voids can affect the quality or performance of printed electronic devices. Therefore, it is important to measure and control the pinholes in printed patterns during the manufacturing process. The pinhole has a three-dimensional (3D) shape and should be measured using a 3D microscope for accurate measurement. However, such equipment is typically too expensive to be acquired by a small-sized company. This paper proposes a measurement method for pinholes in printed patterns, involving pattern images obtained using a relatively inexpensive 2D microscope. The proposed method is based on a pinhole threshold index, which defines the boundary between the pinhole and pattern. The actual measurement results are shown to have varying threshold indices. This research contributes to the advancement of the printed electronics industry.