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The demand for printed electronics (PE) is expected to increase for improved functionality and autonomy of products in the context of the Internet of Things, especially for sensing and communication. With this trend, the environmental performance of novel technologies is of growing importance, and researchers are exploring ways to make them more environmentally friendly using bio-based substrates and additive printing methods. Conductive inks have the highest environmental impact in the life cycle of printed electronics, and there are two options to decrease the impact: increase recycling rates or replace commonly used silver inks with less impactful materials such as copper or graphite. With the current mixed waste management system, a higher recycling rate for silver is not achievable. Copper and graphite have a lower environmental impact than silver, however, the electrical conductivity of copper and graphite inks is lower than silver ink. This article introduces a double-parameter comparison to simultaneously assess the environmental and electrical conductivity of printed electronics using three inks of silver, copper, and graphite inks. Then based on the technical feasibility, this study proposes suitable applications for each substrate and ink combination.

Direct printing methods have been used as manufacturing tools for printed electronics applications due to their cost effectiveness. In this review, the piezo-driven inkjet is discussed in detail since it is a mature technology and suitable for the production printing of printed electronics. In addition, other printing methods are considered for using higher viscosity ink and for producing smaller printed feature size. Various direct printing methods are compared in terms of jet mechanism, printing algorithm, and their applications. In particular high resolution printing methods using high viscosity inks, such as electrohydrodynamic jet, aerosol jet and micro-plotter are reviewed. To understand the recent status of industrial printing applications, display (liquid crystal display and organic light emitting diode) materials and printing issues are discussed. Finally, a brief overview of nano-particle metal based conductive inks is included because these inks have been widely used for printed electronics applications.

This paper presents a new temperature sensor, inkjet-printed with the in-house developed hybrid rGO/Ag nanoparticles ink (rGO/AgNPs ink). Its performance is studied, and the results indicate that its sensitivity is better than the commercial sensor. The meander—shaped electrodes were fabricated using drop-on-demand inkjet printer (Fujifilm Dimatix 2850 printer) on polyethylene terephthalate (PET) substrate. Compared to the sensitivity 0.0543 ?/oc of the sensor developed with commercial ink, the in-house developed sensor shows higher sensitivity 0.1086 ?/oc. Besides, the printed sensors exhibit its resistance increasing linearly with temperature from 30°C to 100°C. The bending tests results also prove that the characteristics of the sensors do not vary significantly, indicating excellent mechanical stability and flexibility. Therefore, the flexible inkjet-printed temperature sensor with the in-house hybrid rGO/AgNPs ink is recommended for the large-scale productions and implementations.

One-step printing of electrically conductive inks on textiles is one of the simplest and most prospective methods to manufacture functional wearable electronics. However, the high surface roughness and porous structure as well as poor temperature endurance of most textiles have become the major challenges for the realization of printed electronic textiles (E-textiles). To solve these issues, the UV curable conductive ink with fast curing and low temperature characteristics was formulated to fabricate the flexible fabric-based conductive patterns using screen printing method. The specific focus was spent on investigating the effect of ink composition on curing speed, film forming ability, morphological characteristics and electrical properties of conductive patterns directly printed on fabric substrates. Firstly, we determined the necessity of defoamer for the formation of uniform and continuous printed textile-based patterns, and optimized the film forming ability of UV-curing ink by exploring the defoamer performance. Then, the ink curing speed was found heavily depending on the different types and contents of photoinitiators. Finally, the nano-silver loading showed critical influence to the screen-printability and the electrical properties of printed patterns. An ink formulation with 60 wt% nano-silver, 4 wt% photoinitiator (1173), and 0.2 wt% defoamer (BYK-555) showed satisfactory screen printability, and the conductive patterns with 1.0 mm width exhibited a remarkably low resistivity of 4.04 × 10−5 Ω cm. Moreover, the high performance of the conductive pattern screen-printed on four different fabrics by the formulated UV curable conductive ink further demonstrated its application potential. The results showed that uniformity and electrical properties of printed patterns were directly related to the weaving method, texture characteristic, and roughness of the textiles. We believe these results will provide basic guidance for the formulation design of conductive ink and facilitate the utility of textiles-based wearable electronics.

Conductive ink is a modern method for making printed circuit boards (PCB’s), with new and somewhat different properties such as electrical conductivity, adhesion on non-conventional surfaces (glass, wood and paper) and the printability it possesses. However, such technology is cost and limited access given the machinery needed for the synthesis of ink and the tax on our currency. This situation leads to an increase in the technological gap between developed and developing countries. Therefore, the objective and motivation of this work is to present InkCo, a machine that automates the process of synthesis of conductive ink from metallurgical and chemical waste of the region. Understanding that through automation, virtual CAD modeling and materials science it is possible to develop the objectives of sustainable development (ODS) 4, 9 and 12, which seek innovation in industry and responsible consumption. Based on these ideas, InkCo is a mechatronic technology product that seeks to reduce this technological gap, through the implementation of rapid prototyping technologies (3D printing, laser cutting and prototyping of controlled circuits), for its structural construction, and thus generate an input (conductive ink) that can be used for the creation of more unconventional technology (3D printing of amorphous circuits on dielectric surfaces).

Chipless RFID (Radio Frequency Identification) tag has attracted significant attention due to the low manufacturing cost. By eliminating the use of integrated circuit (IC), chipless RFID tag can offer competitive price in order to completely replace barcode systems. Besides, integration of physical parameter sensors with chipless RFID will open up a new domain for controlling and monitoring perishable items. It can also be fully printable by using inkjet-printed technology. The inkjet-printed technique is one of the most promising technological solutions for the realization of chipless RFID with low-cost advantage. Various types of conductive inks with different fillers such as metal nanoparticles, carbon nanotubes (CNT), and polymer have been developed for printed electronics. It needs deep investigation and study in designing low-cost but robust by using conductive ink on a low-cost substrate. The aim of this review is to claim research gap related to how AgNP-rGO-PANI (Silver Nanoparticle - Reduced Graphene Oxide - Polyaniline) nanocomposite has both scientific and economic advantages. The inkjet-printed method using conductive inks with nanocomposite fillers synthesized from semiconductor materials such as graphene, silver nanoparticles, and polyaniline on a thin sheet of low-cost substrate. This review provides an overview of synthesis methods of AgNP-rGO-PANI nanocomposite, structure and design of chipless RFID sensor, and chipless RFID sensor fabrication methods.

According to the performance requirements of the multi band compatible antennas for the mobile communication system, the radio frequency identification system, the ultra wideband system and the mobile digital TV system, the present paper originally combined photonic crystal structure, embedded slot fractal, rectangular array antenna, relative dielectric constant gradual thin film, potassium tantalum niobate thin film, Fe-based nanocrystalline alloy coating and graphene conductive ink, and designed a photonic crystal slot fractal array ultra wideband antenna. The result of test indicates that this antenna has strong anti-EMI capability, large performance redundancy and ultra wideband operation capability. This antenna completely covered all working frequency bands of the second generation to the fifth generation mobile communication, the frequency bands of the radio frequency identification system, the frequency band of the ultra wideband system, and the frequency band of the mobile digital TV system. This antenna has small size, high radiation intensity, stable and reliable operation performance; it is a microwave band multi network integration antenna with excellent performance.

Miniaturization of electronic structure for smart textile application has been seen dominated in recent years due to its low cost and light but it requires flexibility to resist stresses. Printing using conductive inks provides the flexibility but it remains a challenge since current printing techniques suffered from ink incompatibility especially on conformal substrates due to its rigidity and low flexibility. An alternative printing technique via syringe-based deposition system is proposed since it capable of printing various materials with different viscosity level. An investigation is required to evaluate its feasibility in printing micro-conductive ink tracks on fabric. The effect of printing and curing parameters including printing speed, deposition height, curing time and temperature to the morphology of the ink tracks and conductivity were investigated. Electrical tests were performed to determine the resistance level. It was found that 0.50 mm width of designated ink track was successfully printed and printing with higher speed reduced the track width while deposition heights affected the thickness of the ink track. Printing speed of 7.00 mm/s with deposition height of 0.59 mm were concluded as the optimum printing parameters. A longer curing time and higher temperature used resulted in lower resistance as expected. The lowest resistance achieved was 1.70 Ω cured at 160°C for 45 minutes. It was proven that a syringe-based deposition system able to print micro-conductive ink track and oven is suitable to cure the ink properly on fabric.

Wearable antenna is part of clothing for transmitting or receiving wireless signals and due to miniaturization, the antenna required to be compact, light, cheap and almost maintenance-free. Syringe-based deposition system with conductive ink is potential to print the antenna structure on fabric as it provides flexibility and compatible with different viscosity of materials. The study is to investigate the printing and curing of conductive inks on fabric using syringe-based deposition system and oven. The effect of printing and curing parameters to morphology and conductivity of the antenna tracks were investigated. Several mechanical and electrical tests were performed to determine the hardness, adhesion and resistance level. It was observed that the antenna tracks were successfully printed according to its designated shape and printing with higher speed caused narrower antenna ink track while pressure differences influenced the thickness of the antenna tracks. The optimum printing parameters obtained was printing at 23 mm/s speed with a pressure of 1 bar to achieve the required antenna track size. The resistance level achieved was considered low at 1.6Ω curing at 160°C for 45 minutes. It was proven that the syringe-based deposition system and oven is capable of printing and curing antenna tracks on fabric.

We propose the inkjet printing of new thin-film transistors (TFTs) based upon a sodium alginate (NaAlg) electrolyte-gate and a new In2O3 nanoparticle ink in which the electrodes and channels were formed by laser ablation. Laser ablation improved the conductive ink channel resolution leading to a smaller channel length through low-temperature processing steps. The NaAlg based electrolyte and a thickness independent gate dielectric allow for an in-plane design resulting in relaxed manufacturing tolerance requirements and reduced processing steps/time. The fabricated TFT operates at a very low voltage (

The paper shows the possibility to print polymer strain gages, microstrip lines, coplanar waveguides, and other prints for avionics using printing technology and equipment. The methods of screen and inkjet printing have been complemented by three new operations of preparing print films for application of an electrically conductive ink layer. Such additional operations make it possible to enhance the conductive ink layer adhesion to the film and to manufacture strain gages for measuring large elongations.

Printed and flexible electronics are definitely promising cutting-edge electronic technologies of the future. They offer a wide-variety of applications such as flexible circuits, flexible displays, flexible solar cells, skin-like pressure sensors, and radio frequency identification tags in our daily life. As the most-fundamental component of electronics, electrodes are made of conductive materials that play a key role in flexible and printed electronic devices. In this review, various inorganic conductive materials and strategies for obtaining highly conductive and uniform electrodes are demonstrated. Applications of printed electrodes fabricated via these strategies are also described. Nevertheless, there are a number of challenges yet to overcome to optimize the processing and performance of printed electrodes.

Future electronics devices are not only smaller and thinner, but are also flexible, bendable and even wearable. This evolution in technology requires direct printing of patterns onto any substrate using conductive inks made of a dispersion of metallic nanoparticles. In this study, Cl- ions was used to induce spontaneous sintering of silver nanoparticles (Ag NPs). Ag NPs with an average diameter of 56 nm were synthesized by polyol method using silver nitrate (AgNO3) and ethylene glycol (EG) as precursor and solvent, respectively. Poly(vinyl pyrrolidone) was used as the capping agent. Water-based inks were formulated containing different Ag NP loading (10–25 wt %). Using 50 mM NaCl aqueous solution as the dispersing medium, an ink with 15 wt % Ag exhibited a sheet resistance of about 2.85 Ω/sq. This very low sheet resistance was attributed to sintering of Ag NPs, which was accompanied by an increase in average diameter of nanoparticles from 56 to 569 nm.

A hydrophilization method for graphite is required for applications such as conductive ink. In typical chemical oxidation methods for graphite have the problems of producing many defects in graphite and a large environmental impact. In recent years, the plasma treatment has attracted attention because of the high quality of the treated samples and the low environmental impact. In this study, we proposed an above-solution plasma treatment with a high contact probability of graphite and plasma since graphite accumulates on the solution surface due to its hydrophobicity, which we compared with a so-called solution plasma treatment. Graphite was hydrophilized via reactions with OH radicals generated by the plasma. It was confirmed that hydroxyl and carboxyl groups were modified to the graphite and the dispersibility was improved. The above-solution plasma achieved more energy-efficient hydrophilization than the solution plasma and it was possible to enhance the dispersibility by increasing the plasma–solution contact area.

Stretchable conducting traces are the key component to realize wearable healthcare electronics; a conductor material that can withstand high strain conditions can be crucial. Here, we describe a simple fabrication pathway to achieve stretchable conductive ink for printing. Specifically, silver flakes and fluorine rubber are amalgamated by the aid of triethanolamine (TEA), which enhanced the compatibility of the components in solution state where methylisobutylketone is the co-solvent. Moreover, TEA plasticizes the composites after the printing and drying of the solvent, causing the composite to deform freely without losing conductivity. The composite exhibits a conductivity value of 8.49 × 104 S m−1 at rest. The printed composite itself is not mechanically resilient after plastic deformation, but it has remarkable adhesion on elastomeric substrates. Thus, the printed ink on elastomers allows stretchable trace that can accommodate repeated stretching/releasing cycles. We fabricate and characterize stretchable printed antenna with three different designs (loop, patch, and bowtie) for the application of skin-adhesive electronics.

To utilize their superior properties, multiwall carbon nanotubes (MWNTs) must be manipulated and aligned end-to-end. We describe a nondestructive method to magnetize MWNTs and provide a means to remotely manipulate them through the electroless deposition of magnetic nickel nanoparticles on their surfaces. The noncovalent bonds between Ni nanoparticles and MWNTs produce a Ni-MWNT hybrid material (NiCH) that is electrically conductive and has an enhanced magnetic susceptibility and elastic modulus. Our experiments show that MWNTs can be plated with Ni for Ni:MWNT weight ratios of γ = 1, 7, 14 and 30, to control the material properties. The phase, atom-level, and morphological information from x-ray diffraction, energy dispersive x-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, dark field STEM, and atomic force microscopy clarify the plating process and reveal the mechanical properties of the synthesized material. Ni metalizes at the surface of the Pd catalyst, forming a continuous wavy layer that encapsulates the MWNT surfaces. Subsequently, Ni acts as an autocatalyst, allowing the plating to continue even after the original Pd catalyst has been completely covered. Raising γ increases the coating layer thickness from 10 to 150 nm, which influences the NiCH magnetic properties and tunes its elastic modulus from 12.5 to 58.7 GPa. The NiCH was used to fabricate Ni-MWNT macrostructures and tune their morphologies by changing the direction of an applied magnetic field. Leveraging the hydrophilic Ni-MWNT outer surface, a water-based conductive ink was created and used to print a conductive path that had an electrical resistivity of 5.9 Ω m, illustrating the potential of this material for printing electronic circuits.

Electrical interconnections are essential for the integration of electronic functions in a fabric. These interconnects can be dispenser printed on a fabric; however printing directly on a breathable woven fabric surface is challenging due to the high surface variation and porosity defined by the weave. This paper, for the first time, experimentally shows that fabric surface variation leads to inconsistent printed structures which adversely affects the electrical properties of printed conductive tracks. It investigates a solution of overcoming the fabric surface variation in the form of dispenser printing an interface layer between the conductive ink and the fabric surface. Four dielectric inks DuPont 5018, Electra EFV4/4965, Fabinks-UV-IF-1004 and Fabinks-UV-TC0233 are quantitatively evaluated, as interface materials, in terms of surface consistency, thickness consistency, repeatability, flexibility, thermal stability and the electrical characteristics of conductive tracks printed on them. All four of the evaluated interface materials significantly reduced the fabric surface variation by more than 95% and provided a suitable low variation surface for printing subsequent electronic layers. Conductive tracks, dispenser printed on the four interface materials, produced ~90% lower electrical resistivity compared to tracks printed directly on the fabric and similar resistivity to dispenser printed tracks on Kapton, a traditional printed electronic substrate. An increased focus on low powered electronics especially for wearables requires the electrical interconnections to dissipate minimum power. The innovative interface layer approach allows fabrication of low resistance electrical interconnections on fabric substrates reducing interconnect power dissipation, making this approach highly suitable for smart fabric applications. Reported details of dispenser printing of interface materials can be used for replicating these results on a range of fabric substrates. The paper also reports a novel thermal imaging based method of analysing resistance distribution within a printed conductive track to assess the geometrical consistency of printed electrical interconnections.

A novel nanocomposite resist is presented based on AgNWs dispersed in poly(methyl methacrylate). It is shown that this nanocomposite resist displays sheet resistances below 10 Ω sq−1 for concentrations of AgNWs higher than and can be used for a wide range of microfabrication techniques. The resist can act as a conductive ink that cures at room temperature, form thin films with low sheet resistances, and be used in fast replication methods derived from soft lithography. Furthermore, it can be applied for nano-scale fabrication via electron beam lithography (EBL) on different substrates, including flexible and insulating materials, providing a straightforward method to avoid charging effects. This, being the first report about a nanocomposite resist based on AgNWs for EBL, describes a simple procedure to account for suspended nanowires, forming bridges, nanocantilevers and more complex nanostructures. A wide range of opportunities opens for the single-step fabrication of electronic components in the nano and micro scale.

Printed-electronics inks belong to a class of novel functional conductive inks that can be used to form high-precision conducting lines or circuits on various flexible substrates. Previous studies have reported conductive inks produced by the reduction and membrane separation method for use in flexible devices. However, it remains a challenge to synthesize conductive inks with high electrical properties at low sintering temperatures, which restricts their range of applications. Herein, we prepare inkjet-printed patterns of conductive inks consisting of Ag nanohexagonal platelets (AgNHPs) as the main component and containing graphene (GE) in different contents. It is found that GE improves the electrical conductivity of the patterns when sintering is done at relatively low temperatures. For instance, when the GE content is 0.15 mg ml(-1), the resistivity is the lowest. When sintering is done at 150 °C, the resistivity (2.7 × 10(-6) Ω · cm) of the GE-AgNHPs conductive ink (GE: 0.15 mg ml(-1)) is 14% of that of the AgNHPs conductive ink; on the other hand, after sintering at 50 °C, this ratio is 2%. It is also found that, with the increase in GE content, the resistivity of the GE-AgNHPs conductive ink increases. This study on GE-AgNHPs conductive inks sintered at low temperatures should further the development of flexible touch screens.

The electrode performance of three types of selected electrically conductive polymers (ECPs), namely polyaniline, polypyrrole (PPy) and poly(3, 4-ethylenedioxythiophene) PEDOT (PSS:PEDOT) composite with multiwalled carbon nanotubes (MWCNTs) were investigated in this study. The capacitor electrode performance has been examined in both three electrodes half-cell and two electrodes device setups. The nano-composites were fabricated via polymerization of pseudocapacitive conductive monomer onto the MWCNT surface through the in situ chemical polymerization approach. Stainless steel thin foils were used as a current collector as well as a flexible backbone. Graphite conductive ink was used as the binder with the composite powder to form a conductive electrode layer. Half-cell electrochemical study was conducted to optimize the weight proportion between MWCNT and ECP in this parametric study. Two-electrode cell electrochemical study assessed the potential performance for the device. MWCNT was found to serve as the framework for polymerization of the ECP into a tubular structure. Among the three composites, it was discovered that the PPy/MWCNT composite has superior capacitor performance up to scan rate of 500 mV s−1.

An innovative electrical current sintering technique is applied to joule-heat conductive ink by increasing current gradually through a stepwise-form. This stepwise electrical sintering technique is devised to overcome thermal damage of printed conductive ink line during electrical sintering due to its high initial resistance. To monitor a stepwise electrical sintering method, in-situ specific resistance was measured. Surface morphology of the sample was observed by field-emission scanning electron microscope. By increasing the current gradually, the conductive line can endure higher current because the specific resistance has dropped gradually during the process. Finally, enhanced final-step current produces lower specific resistance of the conductive line than that obtained from a constant current-supplying electrical sintering method without damaging printed conductive line.

Inkjet printing is an advanced technique which reliably reproduces text, images and photos on paper and some other substrates by desktop printers and is now used in the field of materials deposition. This interest in maskless materials deposition is coupled with the development of microfabrication techniques for the realization of circuits or patterns on flexible substrates for which printing techniques are of primary interest. This paper is a review of some results obtained in inkjet printing technology to develop microfabrication techniques at Laboratory for Nanotechnology (LNT). Ink development, in particular conductive ink, study of printed patterns, as well as application of these to the realization of radio-frequency identification (RFID) tags on flexible substrates, are presented.

To steadily apply conductive inks that contain Cu nanoparticles (NPs) to inkjet printing of patterns at temperatures below 150 °C, the size of the Cu NPs must be reduced. Therefore, we obtained Cu NPs in the range of 9-33 nm, and we studied how their size changes. The variation of the chemical reaction rate changed the size of the Cu NPs for two main reasons. First, the fast transition rate of the Cu precursors at high pH values raises the supersaturation level of the Cu precursor above that of a process with a slow transition rate. The high supersaturation level is generally attributed to the small Cu nuclei and the slow growth caused by their density. Second, the high viscosity of the reaction solution, which occurs because polyvinyl pyrrolidone (PVP) causes an increase in the repulsive force, slows the growth of the Cu NPs at high pH values. The recrystallization temperature of the 9 nm Cu NPs was reduced to 108 °C, and a low specific resistivity of 45 μΩ cm was achieved using the conductive ink prepared with 9 nm Cu NPs at 120 °C. This temperature is significantly lower than those reported for other Cu NP inks. Hence, Cu NP conductive ink could considerably reduce costs because of its apparently low temperature, resolving the main bottleneck of inkjet printing on flexible (polymeric) substrates.

Conductive ink was printed on various microstructured substrates to measure the printing quality. Poly-dimethylsiloxane (PDMS) substrates were used to test the printability of the hydrophobic surface material. Microstructured arrays of 10 ?m regular PDMS cubes were prepared using the MEMS fabrication technique. The gap distance between the cubes was varied from 10 to 40 ?m. The printing wettability of the microstructured surfaces was determined by measuring the contact angle of a droplet of silver conductive ink. Screen-printing methods were used in the conductive line printing experiment. Test line patterns with finely varying widths (30?250 ?m) were printed repeatedly, and the conductivity of the printed lines was measured. The printability, which was defined as the ratio of the successfully printed patterns to the total number of printed patterns, was analyzed as a function of the linewidth and the gap distance of the microstructured surfaces.

To fabricate a low cost, highly conductive ink for inkjet printing, we synthesized a gram scale of uniformly sized Sn nanoparticles by using a modified polyol process and observed a significant size-dependent melting temperature depression from 234.1 °C for bulk Sn to 177.3 °C for 11.3 nm Sn nanoparticles. A 20 wt% of Sn nanoparticles was dispersed in the 50% ethylene glycol: 50% isopropyl alcohol mixed solvent for the appropriate viscosity (11.6 cP) and surface tension (32 dyn cm(-1)). To improve the electrical property, we applied the surface treatments of hydrogen reduction and plasma ashing. The two treatments had the effect of diminishing the sheet resistance from 1 kΩ/sq to 50 Ω/sq. In addition, conductive patterns (1 cm × 1 cm) were successfully drawn on the Si wafer using an inkjet printing instrument with conductive Sn ink. The maximum resistivity for an hour of sintering at 250 °C was 64.27 µΩ cm, which is six times higher than the bulk Sn resistivity (10.1 µΩ cm).

This paper reports progress in the development of strain sensors fabricated using the conductive lithographic film (CLF) printing process. Strain sensitive structures printed via an unmodified offset lithographic printing press using a silver-loaded conductive ink have been deposited concurrently with circuit interconnect, to form an electronic smart packaging system. A system populated with surface mount technology (SMT) components has proven successful in interpreting and logging deformation incidences subjected to a package during testing. It is proposed that with further development such a system could be printed synchronously with packaging graphics using a single printing process to form an integrated time–strain monitoring system.