Search

Printed flexible electrical heaters with excellent heating performance and mechanical durability are highly desirable for deicing and wearable thermotherapy devices. However, the performance of the conventional heaters is stilled limited by low-resolution fabrication methods when applied in high-precision heating in desirable regions. Moreover, the poor conductivity and mechanical stability of the ink also increase the power consumption. Herein, a high-resolution (45 μm) heater with low power consumption was fabricated by a facile electrohydrodynamic (EHD) printing method. A highly printable and stable hybrid conductive ink was obtained by doping PANI nanoparticles into silver flake/thermoplastic polyurethane (TPU) composite. After adding 0.5 wt% PANI nanoparticles into 40 wt% silver flake/TPU composite and low temperature sintering (80 °C), the bulk resistivity decreased from 96.03 × 10−5 Ω·m to 1.26 × 10−5 Ω·m. Thanks to the ultrahigh conductivity of the ink, the EHD printed flexible heater shows high saturation temperature (127.0 °C) under low applied voltage (2 V), wide heating range (33.9 °C~127.0 °C) under a small range of driving voltages (0.5 V ~ 2.0 V), the rapid response time (20 s) and excellent repeatability during 10-time cyclic heating-cooling possess. Furthermore, the printed flexible heaters exhibit great flexibility and durability. The resistance of the heater remains stable after 3000 outer bending cycles with a radius of 0.5 mm, indicating outstanding mechanical stability. Moreover, the heater can be attached to the human body, showing the potential for emerging wearable electronic applications.

Recently, we have demonstrated that hydrogen evolution-assisted (HEA) electroplating can be used for rapid lateral growth of copper across a gap between two copper traces on a printed circuit board (PCB). In this work, the HEA approach has been applied for growing copper traces on three different fabrics of 1000 Denier-Coated Cordura Nylon, Laminated Polyester Ripstop, and 100% Virgin Vinyl. To provide the conductive path for the electroplating, first, the desired pattern was applied as a template on the fabric using a conductive ink including multiwalled carbon nanotubes (MWNTs). The template was then metalized by coating it with copper. The fastest copper lateral growth rate was achieved in 1000 Denier-Coated Cordura Nylon sample (370.96 μm/s), while 100% Virgin Vinyl sample showed the slowest growth rate of 99.57 μm/s. Further study of the morphologies using the scanning electron microscopy technique showed that the material and the texture of the fabric directly affect the morphology of the electroplated copper. The results are very promising for developing a new method of fabricating wearable electronics by directly printing copper on different fabrics.

Silver (Ag) nanoparticles with a mean diameter of about 24.3 nm were synthesized by electroless deposition in an aqueous solution using PAA-Na and ascorbic acid as protective and reducing agents, respectively. The Ag nanoparticles were utilized as conductive ink and sintered at room temperature using different halide solutions (NaCl, NaBr, NaI, LiCl, KCl) at varying concentrations. A significant increase in particle size of about 174–990% was observed after sintering depending on the type of halide solution used. This also led to an increase in the electrical conductivity of the printed Ag pattern. Halide solutions with smaller ionic sizes generally promote the fusing of Ag nanoparticles, which results in larger Ag particles (NaCl > NaBr > NaI) and higher electrical conductivity. The use of an ionic stabilizer (PAA-Na salt) is more effective as a capping agent for Ag nanoparticles. Sintering is also more significant in samples stabilized by PAA-Na compared to those with PAA only.

Electrohydrodynamic (EHD) printing is a promising inkjet technique to generate smaller droplet sizes due to the formation of a Taylor cone. However, the process is intricate and involves the fabrication of a printhead having a smaller nozzle diameter. Notable examples are present in the literature regarding printing through EHD but the underlying phenomenon which is responsible for generating the smaller droplet is obscure. In this work, we present a methodology which highlights the importance of nozzle shape which can govern smaller droplets even with a large head diameter. The work achieves a resolution of less than 2 μ m by fabricating the inkjet head using simple techniques and off-the-shelf inexpensive needles of nozzle diameter ranging from 500 μ m to 250 μ m. The study of various nozzle profiles resulted in a printed resolution which is 50 times smaller than the nozzle diameter. Moreover, the study also highlights the importance of the wetting area profile of the nozzle and explains the role of printhead design which facilitates fine resolution printing of conductive tracks which until now seemed to be obscure.

The fabrication of environmentally friendly printed flexible sensors is still an emerging technology, but with vast potential applications. Among the available printing techniques, inkjet printing is considered as a promising technique for flexible electronics because it enables high volume and versatile manufacturing, at low environmental impact. This study demonstrates a simple and facile method of preparing an environmentally benign water-based conductive ink, by dispersing functionalized and non-functionalized multi-walled carbon nanotubes (MWCNTs) in aqueous solution with the help of a biopolymer surfactant. The concentration of CNTs in the ink formulation was varied from 0.25 to 0.75 wt%, and additives such as triton-x 100, polypropylene glycol, and defoamer were added to achieve desirable ink properties. Inkjet printable ink was produced, and it was observed that the conductivity of the printed pattern is dependent on the printing pass. In addition, it was found that as the number of printing layer increases, there is higher synergy between concentration and number of printing pass in F-MWCNTs printed ink to produce higher electrical conductivity, compared to MWCNTs printed ink. Generally, the findings of this study could potentially open opportunities for global economic growth through the applications of printed, low cost and environmentally friendly flexible sensors.

Made available in DSpace on 2021-06-25T10:27:43Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-06-01 Wireless communication employing radio-frequency identification (RFID) tags is progressively more widespread in a variety of industrial and commercial sectors. Aspects as demanding specific needs regarding reading distance, production cost, and processability are requested for commercial applications. Nowadays, printing of optical barcodes is the most economically technology for short distance (up to ~30 cm) reading applications. However, the large-scale and low-cost printing of RFID tags would be a competitive alternative to barcode technology because it allows quicker identification with much less reading errors. Here we demonstrate a semi-transparent, screen printed RFID antennas using a non-metallic and environmentally friendly conductive paste. The variation of the film thickness (from 2.5 up to 15 µm) permitted the fabrication of antennas with reading range (0.84–3.29 m), sheet resistance (6.2–36 Ω/sq), and optical transmittance (0–32.3%), which are compatible to commercial or industrial applications aiming short to moderate reading distances. Indústria de Tintas Condutivas TICON Flextronics Instituto de Tecnologia (FIT) Institute of Geosciences and Exact Sciences Department of Physics São Paulo State University (Unesp) Institute of Geosciences and Exact Sciences Department of Physics São Paulo State University (Unesp)

This paper presents the production and the characterization of the multi-walled carbon nanotube (MWCNT) printed flexible temperature sensors for high-precision reading in temperature sensing applications. The temperature sensor was fabricated using the inkjet printing method by depositing carbon nanotube (CNT) ink on soft taffeta fabric. An aqueous CNT-based conductive ink was formulated for the inkjet printing process. A translucent polyurethane (PU) welding tape was used as an encapsulation layer on the surface of the sensors to protect sensors from various environmental effects during usage and testing. The fabricated sensors function as thermistors, as the conductivity increases with temperature linearly. The performances of differently patterned three temperature sensors were compared. The highest obtained temperature coefficient of resistance (TCR) and the thermal index are −1.04%/°C and 1135 K, respectively. The fabricated sensors possess a high-temperature sensitivity between room temperature and 50 °C and perform better than the typical commercial platinum temperature sensors and most of the recently reported CNT-based temperature sensors in the literature.

Inkjet printing conductive ink was prepared with the as-prepared silver nanoparticles as conductive fillers and deionized water as the solvent and leveling agent (MY-3000) and silicone defoamer (NXZ) and wetting agent (TRITONX-405) and moisturizer (glycerol) as functional additives. We investigated the effects of viscosity and surface tension of conductive ink and the inkjet print parameters including number of nozzle, print speed, and ink droplet spacing on inkjet printability of conductive ink. The research results show that the inks with the viscosity range of 2.8–9.1 mPa·s and the surface tension of 33.4 mN·m−1 are suitable for inkjet printing. The printing accuracy of the print pattern is related to the number of nozzles and droplet space and the printing layer, but not to the printing speed, but can be changed appropriately to improve the print efficiency. When the mass content of silver nanoparticles is 6.91 wt%, the sheet resistance of the printing pattern with four layers is 2.71 Ω·cm−1, which is in appropriate printing conditions of the inkjet printing voltage of 21 V, printing speed of 60 m· S−1, ink droplet space of 20 μm, and nozzles of 2. The systematic studies of printability and electrical conductivity of inkjet printing silver nanoparticles conductive ink prove the feasibility of the ink and provide some ideas for future applications.

The conductivity of screen printing films at microwave frequency is one of the most important properties of conductive ink when applied in printed electronics. However, the existing methods of conductivity characterization at microwave frequency focus on homogeneous metal films or semiconductors, which are not suitable for conductive composite materials with poor thickness uniformity, like screen printing films. In this research, by applying a classic stripline ring resonator, a rigorous electromagnetic model was set up, and the conductivity of the screen printing film was able to be deduced by comparison between the measurement and simulation results. As a result, the equivalent conductivity of the film is 2 × 106 S/m at 1–3 GHz, which is a little higher than its average direct current conductivity of 1.82 × 106 S/m. This method has been proved to be feasible in measuring the conductivity of screen printing films at microwave frequency. Furthermore, it has great potential in the characterization of other printed conductive composite materials on rough surfaces, like textiles.

Non-contact, direct-write aerosol jet (AJ) printing technology using a variety of functional nanomaterial inks has been regarded as one of the most promising approaches for large-area additive manufacturing. The development and atomization of inks have a considerable effect on the printing quality. Therefore, in this study, the effect of a specific ratio of silver nanoparticle ink and a co-solvent of propylene glycol monomethyl ether (PGME) and ethylene glycol (EG) was investigated. The results indicated that the proportion of the solvent in the silver nanoparticle ink could affect the electrical characteristics of the printed lines. The prepared conductive ink with 95% silver nanoparticle ink and 5% co-solvent at a curing temperature of 180 °C demonstrated superior electrical conductivity and adhesion on the substrate.

Recently, there have been considerable interests in strain sensors that are flexible and stretchable, due to their potential for use in wearable electronics applications. Herein, a facile approach has been employed to produce synergistic strain sensor, taking advantage of the salient properties of hybrid conductive inks produced from graphene and silver nanoparticles (AgNPs). The hybrid ink was inkjet-printed on a polyvinyl alcohol (PVA) substrate. The effect of factors such as amount of graphene, annealing time and printing cycle on the performance of the hybrid conductive ink was investigated. The results showed that an increase in the amount of graphene from 0.1 to 0.5 wt% produced about 90% enhancement in the electrical conductivity of the hybrid ink. However, the change in electrical conductivity values of the hybrid ink at 0.5 wt% and 0.7 wt% graphene content is negligible. On the other hand, it was observed that the electrical conductivity was notably influenced by the number of printing cycle, as well as the annealing time. Significantly, the sensitivity performance of the printed hybrid graphene/AgNPs strain sensor is higher than that of individual graphene and AgNPs printed strain sensors under the strain range up to 20%.

We developed herein a simple and economical high-resolution wiring process on a plastic substrate. High-resolution conductive patterns on the PEI film was fabricated by utilizing the thermal imprint technology and the capillary flow of the conductive ink. An amorphous thermoplastic polyetherimide (PEI) film was thermally imprinted with a metal mold having line (8 μm)/space (12 μm) structures. The effects of the imprint temperature, melting time, and imprint pressure on the PEI film transferability were investigated. A higher replication ratio was obtained when the molding temperature was higher, the melting time was longer, the imprint pressure was higher, and the mold structure height was lower. The mold structures were almost perfectly transferred on the PEI film surface at a molding temperature of 285 °C, a melting time of 3.0 min, and a molding pressure of 1.0 MPa. Two different wiring processes, namely, spin coating and capillary flowing of Ag ink onto the imprinted PEI film, were conducted. For the spin-coating wiring process, the Ag ink existed not only inside the grooves but also on the convex area as the residual layer, regardless of rotational speed and time. For the capillary flowing wiring process, when the Ag ink contacted the edge of the imprinted pattern on the PEI film, it spontaneously flowed toward the wiring direction. Only the concave grooves were selectively filled with Ag ink, and the residual layer was not observed. The fabricated wiring conformed to Ohm’s law, with an electric resistivity of 42 × 10−8 Ω m.

Printed circuit board (PCB) fabrication technology has been widely used in metasurfaces in microwave domain. However, such technology still needs a non-negligible fabricating period and cost. To further explore the ultra-low-cost, convenient processing and fast demonstrating method, we present a metasurface using silver ink to produce the digital patterns for abundant scattering field manipulation. By directly painting the conductive ink on the paper to establish the specific metal structure, arbitrary EM properties can be designed, which could be regarded as a manually convenient PCB technology for metasurface fabrication. We design eight coding sequences to, respectively, generate single- and dual beam fields with different scattering angles. Simulations and measurements show good agreements, verifying the feasibility of our design method. We believe the presented metasurface processing method will promote the interests on flexible metasurface design and further stimulate related domain like wireless communication.

In this paper, humic acid (HA) was used as stabilizer to prepare silver nanoparticles (Ag NPs) by chemically reducing silver salts in water phase, which were employed to produce Ag NPs inks for inkjet printing conductive silver patterns. The obtained silver nanoparticles stabilized with HA (HA-Ag NPs) were all in spherical shape and the particle size was about 7–12 nm. By re-dispersing HA-Ag NPs in ultrapure water, conductive ink with excellent storage stability was prepared, which can be placed at room temperature for 30 days without any precipitation. The as-prepared HA-Ag NPs conductive ink was printed onto photopapers to fabricate conductive silver patterns with a domestic inkjet printer. The resistivity of the printed pattern could reach 135 μΩ cm after printed for 40 layers and sintered at 180 °C for 60 min. In addition, the printed conductive silver patterns could be integrated into a LED device or alarm apparatus, indicating it could be widely used in flexible printing electronics.

Finer nanoplates of silver are prepared by self-assembly on the surface of graphene, and the low-temperature sintered high conductivity ink containing the silver nanoplates is prepared. Most importantly, graphene is added to the solution before the chemical reduction reaction occurs. Firstly, it is found that silver nanoplates have self-assembly phenomenon on the surface of graphene. Secondly, the Ag nano hexagonal platelets (AgNHPs) with small particle sizes (10 nm), narrow distribution and good dispersion are prepared. Especially, smaller sizes (10 nm) and narrower particle size distribution of AgNHPs particles can be easily controlled by using this process. Finally, the conductivity of the ink is excellent. For example, when the printed patterns were sintering at 150 °C, the resistivity of the ink(GE: 0.15 g/L) reached the minimum value of 2.2×10−6 Ω·cm. And the resistivity value was 3.7×10−6 Qcm, when it was sintered at 100 °C for 30 min. The conductive ink prepared can be used for the field of printing electronics as ink-jet printing ink.

Printed electronics involve a process of creating electrical devices by printing with conductive ink on flexible substrates. This process is environmentally-friendly and affordable, and thus suited for mass production. Roll-to-roll printing is a common method classified under printed electronics. This method uses a roll to apply pressure to film or metallic foil, and prints with conductive ink. To commercialize printed electronic technology using roll-to-roll printing, it is necessary to improve the superposition accuracy. Superposition accuracy refers to the position error between the layers. If the superposition accuracy is poor, the product quality drops due to electrical interference resulting from misalignment. To enhance the superposition accuracy of printed electronics, precise measurements of the web position must initially be obtained. In a previous study, this issue was resolved through the development of a position measurement system for precision alignment. This study improves the web position measurement system of the preceding study by applying a burst alignment pattern. The burst alignment pattern expands the linear measurement range of the optical encoder, and the directions of errors can be determined through signal analysis.

Cu-based conductive inks are more cost effective than silver-based ones for flexible electronics. However, it is challenging to simultaneously ensure the mechanical flexibility, environmental oxidation durability, and low resistance of the sintered Cu electrodes. To achieve this goal, Cu-based conductive inks including silane coupling agents are developed and used to produce flexible Cu electrodes on cellulose paper after air–atmosphere sintering. The key factor to achieve the mechanical flexibility and environmental oxidation durability at the same time is the use of aminoethyl-aminopropyltrimethoxysilane (AEAPTMS) or 3-glycidoxypropyltrimethoxysilane (GPTMS). Negligible resistance change is observed in the sintered Cu electrode with AEAPTMS, even after 1000 repeated bending cycles with a bending radius of 5 mm and exposure at 60 °C/80% RH for 7 days. Especially, Cu electrodes produced using GPTMS show improved flexibility with negligible resistance change even after 10,000 bending cycles. To demonstrate the applicability of these Cu electrodes, a flexible paper-based movement sensor is successfully fabricated from the present Cu-based ink. This approach using silane coupling agents will contribute to the reliable operation of Cu-based flexible devices with high mechanical and environmental durability.

In this paper, a bump-forming method for flip chip bonding using ink-jet printing technology is proposed. A flip chip bonded transmission line using ink-jet printed silver bumps consisting of conductive ink containing silver nanoparticles was fabricated to verify the electrical characteristics after the flip chip bonding process. The transmission line was designed according to microstrip theory for a frequency range of 300 kHz to 3 GHz, with the size of fabricated line being 35 (width) × 8.64 (length) × 0.5 (thickness) mm3. The electrical characteristics of a reference microstrip and the flip chip bonded line were compared with FEM simulation and measurement results. Direct current (DC) resistances of both the reference line and the flip chip bonded line were measured to be 3.1 Ω and 3.2 Ω, respectively. The discrepancy between measured insertion loss and the simulation result was only 0.04 dB at 3 GHz, and the return loss was greater than 15 dB in the measurement frequency range. As a result of the analysis, it was confirmed that the DC resistance of ink-jet printed bumps account for 0.56% of the total DC resistance, and the ink-jet printed bumps hardly affected the radio frequency (RF) characteristics of the RF transmission line at low frequencies. The results demonstrate that ink-jet printed silver bumps can be used for a simple and low-cost flip chip bonding process. We expect that the proposed method can be applied to the packaging of various electronics such as flexible, wearable devices and RF applications.

Copper–silver hybrid conductive inks can combine the advantages of lower cost, better conductivity and long-term stability of the copper or silver ink, which have attracted wide research interest in the development of materials for flexible electronics. Although Cu–Ag nanoparticle based inks, such as Cu–Ag core–shell nanoparticle inks and Cu–Ag bimetallic nanoparticle inks, have already been developed and applied to produce conductive patterns using different deposition methods, they are still not ideal because of the complex and time-consuming synthetic process, low yield and high sintering temperature for good conductivity. In this paper, we report synthesis and characterization of novel self-catalyzed Cu–Ag organic complex inks with reduced sintering temperature via a simple one-step method. The effects of Cu–Ag ratio on the thermal property, stability and electrical performance of the formulated inks were investigated, where the Cu1–Ag1 ink was found to be ideal in terms of cost, conductivity and thermal behavior. The presence of silver oxalate in the copper complex ink was beneficial to the thermal decomposition of the Cu complex and able to decrease the sintering temperature by 30 °C due to the catalytic function of silver, making it more compatible with flexible polymer substrate materials. Meanwhile, the addition of a small amount of silver oxalate could improve the conductivity of the Cu ink. The sintered Cu–Ag films showed favorable conductivity which is comparable to the value of the reported Cu–Ag nano inks but with a lower sintering temperature. The Cu1–Ag1 hybrid ink with self-catalyzing capability is a balanced choice when considering the cost and conductivity.

A microwave-assisted two-steps method was proposed for the facile and fast preparation of silver nanoparticle conductive ink. The nanoparticles in the ink are of multi-sized, which is beneficial to getting higher packing density and better conductivity of the printed/written pattern. The effects of the reaction parameters of microwave and additives on the written pattern resistivity were studied on the basis of scanning electron microscope, X-ray diffraction and surface porosity results. Both of the microwave energy and the addition of PVP as the capping agent were found to be critical for the formation of face-centered cubic silver nanoparticles in the conductive ink. The surface porosity and the pore distribution form were also demonstrated to affect the pattern conductivity. The electrical resistivity or the pattern written with the ink prepared at microwave irradiation time of 90 s was calculated to be 364 μΩ cm. The second step of simple centrifugation process could improve the pattern conductivity effectively. After concentrated the conductive ink for two times, the electrical resistivity of the written pattern reduced from 364 to 77 μΩ cm. The proposed two-steps of microwave combined with centrifugation method is a simple and useful way for the preparation of silver nanoparticle conductive ink that can be used in printed electronics.

A novel complex ink was fabricated by mixing Sn–58Bi nanoparticles with a commercial conductive ink containing Ag nanoparticles and then sintered rapidly for 110 s at 140 °C in air using a conveyor-type reflow furnace. Sn–58Bi nanoparticles smaller than 15 nm wetted on the neighboring Ag nanoparticles immediately after melting at temperatures lower than their melting point, and hence, acted as transient liquid-phase binders. The composite film sintered with 4 wt% Sn–58Bi exhibited stability and a low electrical resistivity of 4.46 μΩ cm, and hence, was found to be compatible with low-cost flexible films.

The capabilities of conductive ink with both excellent conductivity and flexibility properties are extremely important for the construction of next-generation flexible electronic devices. However, the development of an appropriate ink possessing high conductivity and good dispersity remains a big challenge for ink-jet printing. Here, an original synthesis method of surfactant-free carbon black@graphene (CB@rGO) conductive ink is reported via freeze-drying process and reduction in p-phenylenediamine. The CB@rGO ink unambiguously displays a well-defined and smooth morphology, extremely the CB@rGO conductive particles showing good stability in many solvents. The CB@rGO film exhibited outstanding flexibility which is showed by the durable conductivity after bending 1000 times. Furthermore, it has an excellent conductivity of 714 ± 90 S m−1, and these data increased to 5091 ± 200 S m−1 after the high temperature post-processing increased by 198% compared to the traditional rGO film. Notably, the absence of surfactant in conductive fillers’ dispersing process contributed to the high conductivity of CB@rGO ink compared with the traditional ones.

International audience; The promising and extraordinary properties of graphene have attracted significant interest, making graphene an alternative to replace many traditional materials for many applications, particularly in conductive ink for the fabrication of flexible electronics. For the past 10 years, numerous studies have been reported on the synthesis of graphene conductive ink for printing on flexible substrates for various electronic applications. The development of graphene-based ink is reviewed, with the main focus on the types of graphene-like materials in conductive inks, and the compositions and important properties of those inks. Another intention behind this review is to compare the pros and cons of graphene-based ink with those using other common conductive materials, such as gold nanoparticles, silver nanoparticles, copper nanoparticles, conductive polymers and carbon nanotubes. Recent works on graphene hybrid-based ink containing other metallic nanoparticles as an alternative way to improve the electrical properties of the conductive inks are also reported. Brief comparisons between inkjet printing and other printing techniques for the fabrication of flexible electronics are discussed.

Direct ink writing is an interesting and attractive method to replace traditional fabrication techniques such as etching, milling, and lithography for flexible electronics because of its simple process, low cost, green nature, and good prospects for development and application. In this work, graphene/polypyrrole (G/P) binary conductive material was prepared by in situ polymerization of pyrrole monomer and graphene oxide with vitamin C (VC) as green reducing agent. Then graphene/polypyrrole/carbon black (G/P/CB) conductive ink was fabricated using a mixture of alcohol, ethylene glycol, glycerol, and deionized water as solvent. Electronic circuits were obtained by directly writing the prepared conductive ink on flexible substrate, high-gloss photographic paper. When the loading of G/P binary conductive material, carbon black, ethanol, ethylene glycol, glycerol, sodium carboxymethyl cellulose, and deionized water was 54 mg, 546 mg, 12 mL, 30 mL, 30 mL, 480 mg, and 51 mL, the electrical conductivity, solid content, contact angle, and viscosity was 146.3 μS/cm, 4.3%, 34.6°, and 35.8 mPa s, respectively. The ink exhibited excellent water and acid resistance, and the electronic circuit written using the ink showed good uniformity and mechanical flexibility. Scanning electron microscopy evaluation of cross-sections of G/P/CB ink lines on photographic paper and light-emitting diode experiments confirmed that the three-dimensional flexible paper-based conductive circuits containing 9 wt.% G/P formed a complete electrical network.

Conducting polymers, such as the p-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), have enabled the development of an array of opto- and bio-electronics devices. However, to make these technologies truly pervasive, stable and easily processable, n-doped conducting polymers are also needed. Despite major efforts, no n-type equivalents to the benchmark PEDOT:PSS exist to date. Here, we report on the development of poly(benzimidazobenzophenanthroline):poly(ethyleneimine) (BBL:PEI) as an ethanol-based n-type conductive ink. BBL:PEI thin films yield an n-type electrical conductivity reaching 8 S cm−1, along with excellent thermal, ambient, and solvent stability. This printable n-type mixed ion-electron conductor has several technological implications for realizing high-performance organic electronic devices, as demonstrated for organic thermoelectric generators with record high power output and n-type organic electrochemical transistors with a unique depletion mode of operation. BBL:PEI inks hold promise for the development of next-generation bioelectronics and wearable devices, in particular targeting novel functionality, efficiency, and power performance., The development of n-type conductive polymer inks is critical for the development of next-generation opto-electronic devices that rely on efficient hole and electron transport. Here, the authors report an alcohol-based, high performance and stable n-type conductive ink for printed electronics.

Printable electronics is a promising manufacturing technology for the potential production of low-cost flexible electronic devices, ranging from displays to active wear. It is known that rapid printing of conductive ink on a flexible substrate is vulnerable to several sources of variation during the manufacturing process. However, this process is still not being subjected to a quality control method that is both non-invasive and in situ. To address this issue, we propose controlling the printing accuracy by monitoring the spatial distribution of the deposited ink using terahertz (THz) waves. The parameters studied are the printing speed of an industrial roll-to-roll press with flexography printing units and the pre-calibration compression, or expansion factor, for a pattern printed on a flexible plastic substrate. The pattern, which is carefully selected, has Babinet’s electromagnetic transmission properties in the THz frequency range. To validate our choice, we quantified the geometric variations of the printed pattern by visible microscopy and compared its accuracy using one-dimensional THz spectroscopy. Our study shows a remarkable agreement between visible microscopic observation of the printing performance and the signature of the THz transmission. Notably, under specific conditions, one-dimensional (1D) THz information from a resonant pattern can be more accurate than two-dimensional (2D) microscopy information. This result paves the way for a simple strategy for non-invasive and contactless in situ monitoring of printable electronics production.

A facile one-step microwave approach was employed to synthesize silver nanoparticle (AgNP) conductive ink. The conductive ink contained multi-sized silver nanoparticles. Different particle size distribution can be obtained by adding different amounts of the silver source. The relationship between the conductivity of the direct written pattern using the as-prepared silver conductive ink, the particle packing morphology and the particle size distribution standard deviation was investigated. Among all the samples, conductive ink with a silver weight percentage of 10% can have an optimal electrical resistance of 98 μΩ cm after post-hot/pressure treatment at 100°C and 20 MPa for 10 min. The as-prepared conductive ink is of potential application in printed electronics because the sintering condition of low temperatures is feasible for most kinds of flexible substrate materials.

Silver conductive ink using silver oxalate as silver precursor has attracted considerable research interest due to its unique properties. However, silver oxalate has poor dissolvability in organic solvents and high thermal decomposition temperature, the latter is not desirable for pattern formation on some low cost polymer based flexible substrates. In this paper, different kinds of alkylamine were chosen as ligands to formulate silver oxalate inks to address the mentioned issues. The role of amines in silver oxalate based inks was studied in detail. The influence of amine types on thermal property, stability and electrical performance of the formulated silver oxalate inks was investigated. The relationships between them were established and elucidated. The results show that highly conductive silver films with controlled microstructure features can be achieved for low temperature sintering by selection of an appropriate amine as the latter has a strong influence on the decomposition temperature of the formed silver–amine complex and it determines the nucleation and growth of silver particles in the film formation process. The chemical reactions occurring within the ink were also studied. An optimal silver complex ink was prepared by using blended amines as ligands finally, producing a uniform silver film with good quality and favorable conductivity at 150 °C. The results are important for future design of stable and high conductive silver complex inks for practical applications.

Water-dispersible copper nanoparticles (Cu NPs) with good antioxidation properties are facilely synthesized in aqueous solution without inert gas protection employing tannic acid (TA) as the stabilizer and protectant. The sizes of as-prepared tannic acid capped copper nanoparticles (TA-Cu NPs) are in the range of 20–40 nm with a narrow size distribution. Owing to the protection of TA layer, TA-Cu NPs exhibit excellent anti-oxidation power and no oxidation was observed even after being stored under ambient conditions for 90 days. In addition, homogenous Cu NPs inks could be synthesized via the simple dispersion of TA-Cu NPs in water, which can be inkjet-printed onto flexible substrates into conductive patterns using a common color printer.

Size-controllable copper nanomaterials were easily obtained via an improved polyol process by regulating the dosage of copper source and reducing agent. The monodisperse copper nanoparticles with strong antioxidation properties were employed as fillers to fabricate conductive ink. The copper-based ink could be screen-printed onto flexible substrates, which shows persistent stability and uniform properties without color change for a few days. After heating at 240 °C (40 min) in N2 atmosphere, a low electrical resistivity of 16.2 μΩ cm was obtained for the copper nanomaterial-based conductive pattern.

The creation of more robust biocompatible printed electronics devices requires an understanding of interactions between conductive inks and substrates to achieve desired printing and functional properties. In this study, we present a water-based conductive ink that can provide a readily achieved thin film deposition on a highly hydrophobic surface such as poly(dimethylsiloxane) (PDMS). We also show that surface treatments with atmospheric plasma can be utilized to tailor the surface energy of hydrophobic substrates to improve the deposition of inks not custom made for such applications. By using a tailored Ag nano-particle ink, we have successfully printed conductive traces onto a hydrophobic (PDMS) substrate without any surface modification. It was also shown that when introducing atmospheric plasma treatment to the PDMS substrate prior to printing with the tailored ink poor printing resulted. The proposed mechanism for the cause of this poor wetting and deposition is an adverse interaction between the ink and PDMS surface caused by surface oxidation resultant of plasma treatment. The results show that the generally accepted rule that a difference between the substrate and ink surface energy of 10 mN/m for good print quality does not necessarily hold true in the case of functional printing.

Microheater array powder sintering (MAPS) is a novel additive manufacturing process that uses an array of microheaters to selectively sinter powder particles. MAPS shows great promise as a new method of printing flexible electronics by enabling digital curing of conductive inks on a variety of substrates. For MAPS to work effectively, a microscale air gap needs to be maintained between the heater array and the conductive ink. In this article, we present an experimental MAPS printer with air gap control for printing conductive circuits. First, we discuss design aspects necessary to implement MAPS. An analysis is performed to validate that the design can maintain the desired air gap between the microheaters and the sintering layer, which consists of a silver nanoparticle ink. The printer is tested by printing conductive lines on a flexible plastic substrate with silver nanoparticle ink. Results show MAPS performs on par with or better than the existing fabrication methods for printed electronics in terms of both the print quality (conductivity of the printed line) and print speed, which shows MAPS’ great promise as a competitive new method for digital production of printed electronics.

Favorable conductivity at low temperature is desirable for flexible electronics technology, where formulation of a suitable ink material is very critical. In this paper, a type of silver organic decomposable ink (10 wt.% silver content) was formulated by using as-prepared silver oxalate and butylamine, producing silver films with good uniformity and conductivity on a polyimide substrate after sintering below 130°C (15.72 μΩ cm) and even at 100°C (36.29 μΩ cm). Silver oxalate powder with good properties and an appropriate solid amine complex with lower decomposition temperature were synthesized, both differing from those reported in the literature. The influence of the factors on the electrical properties of the produced silver films such as sintering temperature and time was studied in detail and the relationship between them was demonstrated.

Inkjet ink based on silver nanoparticles with sizes of 11.1 ± 2.4 nm has been developed. Test images are printed on a laboratory inkjet printer, followed by sintering the printed patterns with a diode laser having a wavelength of 453 nm. The structure and electrical properties of the resulting films are studied depending on the parameters of laser sintering. It is found that under optimal conditions, an electrically conductive film with a low resistivity of 12.2 μΩ· cm can be formed.

A facile, green method for fabrication of conductive ink composed of Ag flakes was developed for use in flexible printed electronics. The Ag flakes were prepared using AgNO3, nontoxic l-ascorbic acid (Vc) and polyvinylpyrrolidone (PVP) serving as a metal salt, reducing agent and capping agent, respectively. The prepared Ag flakes were characterized by XRD, SEM, and TGA. The combination of PVP and FeCl3 was found to be critical for the formation of the Ag flakes, and reaction activity was affected by temperature. Samples obtained at 140 °C were composed of Ag flakes with an average size of 0.94 ± 0.3 μm. A new fabrication method for producing conductive patterns was designed using a syringe with varying dispersion areas, allowing the ink (Ag flakes and organic solvent) to be applied directly onto a flexible photo paper. The conductivity and flexibility of the pattern were experimentally tested under varying reaction temperatures and bending cycles. Increasing contact area and packing density between Ag flakes resulted in an improved conductivity of the bending pattern. After more than 5000 bending cycles, the patterns were sintered at 160 °C and the resistivity increased from 4.6 ± 0.6 to 22.4 ± 0.8 μΩ cm, acceptable values for practical applications. Sample conductive lines drawn by the Ag flake ink exhibited excellent conductive performance and mechanical integrity, demonstrating a promising method for the formation of flexible microelectrodes or electronic devices.

Flexible electronics is of considerable interest for many applications due to the distinctive features of low-cost, flexibility and light weight capabilities. However, in translating the technology from research to practical applications one faces many challenges. One of them is to formulate suitable ink materials where the selection of functional components, for example in the case of organic silver ink, the silver precursor, complexing agent and volatile organic solvent, are very critical because these constituents determine the final properties of the ink. In this paper, a new type of silver organic ink with decomposition and self-reduction mechanisms (10 wt% silver content) was formulated. It is shown that the ink is capable of producing silver films with good uniformity and conductivity on a polyimide substrate after sintering at 155 °C. The effect of solvent on the thermal property of the formulated ink have been investigated by differential scanning calorimetry (DSC) and UV–Vis spectrscopy, where the active roles of the solvents and the underlying chemical reactions in the ink during heating were studied. The reaction mechanism between the complexing agent and the silver precursor was confirmed by FT-IR measurements. The effects of sintering temperature and time on the microstructure and electrical properties of the silver ink films have been studied in detail using XRD, SEM/EDX and 4-probe based techniques. The defects such as voids and cracks as well as the coffee rings, which are often associated with films produced from organic silver inks, were reduced significantly by using both decomposition and self-reduction mechanisms in film formation.

Monodisperse silver nanoparticles with high concentration are successful synthesized by a modified polyol process under a relatively low mass ratio of PVP to AgNO3. The obtained silver nanoparticles with excellent stability and dispersity possess a mean diameter of about 118 nm and the yield reach to 80 wt%. Then, using the as-prepared silver nanoparticles as filler together with other additives, conductive inks were formulated. This kind of conductive ink could be screen-printed on polyimide substrates to obtain a series of electrical conductive circuits. A relatively low resistivity of 8.3 × 10− 6 Ω·cm which was only five times larger than that of bulk silver was achieved under sintering at 220 °C for 30 min under air atmosphere. Meanwhile, the electrical conductive circuits kept outstanding mechanical performance. So this silver nanoparticles filled electrical conductive inks has the potential applications in flexible wearable devices.

Conductive ink can be widely applied in printed electronics to print high conductivity and flexible electrodes, especially for large-area formats with low cost considerations. In this article, we demonstrated that the in situ prepared silver nanoparticles decorated graphene conductive ink was suitable for flexible electronics. By using liquid phase exfolication method and reducing the silver salt to nano silver at the same system which addressed the heterogeneous issue of silver decorated graphene. The inkjet-printed graphene features attained low resistivity of 20 ± 1Ω/□ after a thermal anneal at 400 °C for 30 min while showed uniform morphology, compatibility with flexible substrates.

Due to low melting temperature, low price and high conductivity, copper nanoparticles have great potential to substitute conductive polymers, silver and gold nanoparticles and others in conductive inks. Here we developed a new, simple and green method to synthesize copper nanoparticles, which have the average size of around 140 nm and show remarkable ability to prevent oxidation. Using the copper nanoparticles for conductive ink, the electrical performance of copper film by depositing copper ink on polyimide was also investigated with the sintering temperature from 150 to 400 °C. The electrical resistivity is around 17.0 μΩ cm under sintering temperature of 250 °C, and can reach as low as 5.7 μΩ cm under the temperature of 400 °C. The proposed approach to synthesize copper nanoparticles for high performance conductive ink presents potential applications in flexible electronics.

Conductive inks based on graphite and carbon black are used in a host of applications including energy storage, energy harvesting, electrochemical sensors and printed heaters. This requires accurate control of electrical properties tailored to the application; ink formulation is a fundamental element of this. Data on how formulation relates to properties have tended to apply to only single types of conductor at any time, with data on mixed types of carbon only empirical thus far. Therefore, screen printable carbon inks with differing graphite, carbon black and vinyl polymer content were formulated and printed to establish the effect on rheology, deposition and conductivity. The study found that at a higher total carbon loading ink of 29.4% by mass, optimal conductivity (0.029 Ω cm) was achieved at a graphite to carbon black ratio of 2.6 to 1. For a lower total carbon loading (21.7 mass %), this ratio was reduced to 1.8 to 1. Formulation affected viscosity and hence ink transfer and also surface roughness due to retention of features from the screen printing mesh and the inherent roughness of the carbon components, as well as the ability of features to be reproduced consistently.

In this work, dendritic silver nanostructure (DSN) was synthesized via a novel and eco-friendly method. The effects of the dosage of clove oil, concentration of silver nitrate and ultrasonic time on the formation of DSN were discussed. The structures of the obtained products were characterized by X-ray power diffraction, field emission scanning electron microscopy, transmission electron microscopy, and the chemical composition of DSN was examined by energy dispersive X-ray spectroscopy. The results show that the length of the trunks is approximately 2–5 μm and that of the lateral branches is about 0.5–2 μm. The conductive inks filled with dendritic silver and sphere silver powders were prepared respectively at mass fraction of 60%. The result shows that the coating of the conductive ink filled with dendritic silver has a lower sheet resistance of approximately 0.07 Ω/□ at a thickness of 20 μm.

In the present study, Cu colloidal nanoparticles and nanopowders were successfully synthesized by a pulsed wire evaporation process. Cu-based nano-inks were prepared by mixing Cu nanoparticles with acrylic resin and solvent. Cu nanoparticles with a particle size of

Paper-based flexible electronics/circuit have a bright potential in displays, transistor and sensors due to low cost and disposability. Here we presented a facile microfabrication method for paper-based flexible electronics with flash foam stamp lithography (FFSL), which can be implemented in resource-limited laboratory. Only two steps are needed. Firstly, negative patterns of circuit are stamped on the paper with polydimethylsiloxane (PDMS) ink to form hydrophobic barriers after PDMS is solidified. Then the patterned paper is immersed in the conductive ink to absorb ink and acquire circuits. In this paper we present foldable, waterproof and multi-layer paper-based flexible electronics can be easily fabricated. Also as FFSL can be also directly used in fabrication of microfluidic paper-based analytical devices (μPADs), this method has a promising potential in fabricating electrodes of μPADs.

The reciprocating needle dispensing technique is capable of patterning functional inks with a wide range of viscosities. As injections are performed by extruding an ink driven by the reciprocating needle motion, the mechanical specifications and the ink properties are expected to influence the amount of ink conveyed by the needle, thereby affecting the size of drops formed on a substrate. Needle dispensing tests were performed by using Newtonian silicone oils of different viscosities and a pseudoplastic conductive ink with various needle speeds and positions of the needle and the ink reservoir. Time-resolved analysis of the dispensing motions indicated that the formation of the dynamic meniscus around the needle was primarily described by the Landau–Levich–Derjaguin ink-coating theory. However, a slight modification that accounted for the initial gap between the needle and the glass capillary was needed to precisely describe the ink extrusion behaviors. The scaling analysis presented herein provides a perspective for the precise control of drop formation via optimal tuning of the ink injection. Regarding ink filament pinch-off, we discovered that the pseudoplastic liquid exhibited a faster pinch-off at higher needle retraction speed, which is attributed to a reduction of the apparent viscosity due to shear thinning. This behavior is preferable for needle dispensing with better stability.

In this paper, we propose a high gain antenna operating over dual band of 900 MHz and 2.4 GHz. The proposed antenna is designed by finite element method (FEM) based Ansys high frequency structure simulator (HFSS). We use conductive ink of silver nanoparticles (AgNPs) and commercial Dimatix material inkjet printer (DMP-3000) to print the proposed antenna on 50-micron thick, transparent and flexible polyethyleneterephthalate (PET) substrate. To characterize the fabricated antenna, we use vector network analyzer (VNA) and obtain reflection coefficients of −16.4 dB at 900 MHz and −26 dB at 2.4 GHz, which accord with the HFSS simulation results. HFSS simulated results provide antenna gains as high as 16.74 and 16.24 dBi at 900 MHz and 2.4 GHz, respectively and 23.33 and 11.66 % of −10 dB fractional bandwidth at 900 MHz and 2.4 GHz, respectively. These results suggest that the proposed high gain antenna can be used for dual band Wi-Fi and wearable devices as well.

Printed electronics is being explored as a rapid, facile means for manufacturing thermoelectric generators (TEGs) that can recover useful electrical energy from waste heat. This work examines the relevant electrical conductivity, thermal resistance, thermovoltage, and Seebeck coefficient of printed films for use in such printed flexible TEGs. The thermoelectric performance of TEGs printed using commercially relevant nickel, silver, and carbon inks is evaluated. The microstructure of the printed films is investigated to better understand why the electrical conductivity and Seebeck coefficient are degraded. Thermal conduction is shown to be relatively insensitive to the type of metalized coating and nearly equivalent to that of an uncoated polymer substrate. Of the commercially available conductive ink materials examined, carbon–nickel TEGs are shown to exhibit the highest thermovoltage, with a value of 10.3 μV/K. However, silver–nickel TEGs produced the highest power generation of 14.6 μW [from 31 junctions with temperature difference (ΔT) of 113°C] due to their low electrical resistance. The voltage generated from the silver–nickel TEG was stable under continuous operation at 275°C for 3 h. We have also demonstrated that, after a year of storage in ambient conditions, these devices retain their performance. Notably, the electrical conductivity and Seebeck coefficient measured for individual materials were consistent with those measured from actual printed TEG device structures, validating the need for further fundamental materials characterization to accelerate flexible TEG device optimization.

Flexible zinc-air batteries were fabricated using an inexpensive screen-printing technique. The anode and cathode current collectors were printed using commercial nano-silver conductive ink on a polyethylene terephthalate (PET) substrate and a polypropylene (PP) membrane, respectively. Air cathodes made of blended carbon black with inexpensive metal oxides including manganese oxide (MnO2) and cerium oxide (CeO2), were studied. The presence of the metal oxides in the air cathodes enhanced the oxygen reduction reaction which is the most important cathodic reaction in zinc-air batteries. The battery with 20 %wt CeO2 showed the highest performance and provided an open-circuit voltage of 1.6 V and 5 – 240 mA.cm-2 ohmic loss zone. The discharge potential of this battery at the current density of 5 mA.cm-2 was nearly 0.25 V higher than that of the battery without metal oxides. Finally, the battery was tested for its flexibility by bending it so that its length decreased from 2.5 to 1 cm. The results showed that the bending did not affect characteristics on potential voltage and discharging time of the batteries fabricated.

As one of the most important conductive materials, silver nanowires have recently attracted a lot of attention for potential applications such as electrically conductive adhesives, transparent electrodes, and conductive ink. In this paper, silver nanowires with a diameter of 200–570 nm and a length of 20–100 μm were synthesized by a polyol process. The electrically conductive adhesives (ECAs) composed of an epoxy-based binder containing silver nanowire were prepared and the curing behaviors and electrical properties of ECAs were investigated. The in situ monitoring of the variation in electrical resistance of the ECAs explore that silver nanowires impact on the curing behavior of the ECAs. The resistance of the ECAs filled with 40 wt% silver nanowires reaches to 0.59 Ω heated to 11 min from the room temperature to 164 °C. Silver nanowires significantly improve the electrical conductivity of the ECAs, and the resistivities of the ECAs filled with 35 and 40 wt% silver nanowires is 9.48 × 10−4 and 1.42 × 10−4 Ω cm after cured at 168 °C, respectively. The reasons for the effects of silver nanowires on the curing behavior and the electrical properties were also discussed in terms of the morphology and higher activity of silver nanowires.

In this study, the thermal kinetics of Ag nanoparticles (NPs) with different capping agents was studied during self-aggregation and self-assembly, which is important for the usage of Ag conductive ink. Ag NPs were synthesized with polyvinylpyrrolidone (PVP) and l-Cysteine (L-cys) as capping agents. After self-aggregation and self-assembly by heat treatment, the Ag nanoparticles fabricate a homogeneous surface morphology. By TG measurements, the equations of thermal kinetics were established. Flynne Walle Ozawa model was used to calculate the activation energies of self-aggregation and self-assembly of Ag/PVP and Ag/L-cys. The activation energy values have showed a continuous increase as a function of degree of conversion. The activation energy value for Ag/PVP is smaller than Ag/L-cys because PVP binds weaker to the silver nanoparticle surface than thiols.

Fully inkjet-printed three-dimensional (3D) objects with integrated metal provide exciting possibilities for on-demand fabrication of radio frequency electronics such as inductors, capacitors, and filters. To date, there have been several reports of printed radio frequency components metallized via the use of plating solutions, sputtering, and low-conductivity pastes. These metallization techniques require rather complex fabrication, and do not provide an easily integrated or versatile process. This work utilizes a novel silver ink cured with a low-cost infrared lamp at only 80 °C, and achieves a high conductivity of 1×107 S m−1. By inkjet printing the infrared-cured silver together with a commercial 3D inkjet ultraviolet-cured acrylic dielectric, a multilayer process is demonstrated. By using a smoothing technique, both the conductive ink and dielectric provide surface roughness values of