Conductive Silver Ink Research Articles

Low Cost Paper-based Electrochemical Sensing Platform for the Determination of Hydrogen Peroxide

A rapid, precise, low cost, selective and sensitive paper-based electrochemical device for the determination of H2O2 in milk is described here. Commercially available varnish and a simple hand drawing method were used to develop the hydrophobic pattern to generate a hydrophilic detection zone on the filter paper. The electrode system was fabricated on the detection zone in order to detect H2O2 electrochemically. A commercially available graphite pencil and conductive silver ink were used to fabricate the counter electrode and pseudo-reference electrode, respectively. A paste of Prussian blue (PB) modified graphite, unmodified graphite and phenol-formaldehyde polymer were used to fabricate a PB modified graphite working electrode on paper. This modified electrode showed electrocatalytic activity towards the reduction of H2O2 and it was successfully used for the chronoamperometric detection of H2O2 at 0 V vs Ag reference electrode in 0.1 mol l-1 phosphate buffer, buffered at pH 6.0 in 0.1 mol l-1 KCl. Under optimum conditions, the calibration curve for the H2O2 determination was linear from 5 to 50 mmol l-1 with a detection limit (LoD = x ̅ + 3SD) of 4.0 mmol l-1. In addition, the PB modified graphite electrode showed selectivity for H2O2 detection in the presence of ascorbic acid, sucrose and citric acid.

Robust physiological signal monitoring by a flexible piezoresistive sensor microstructured with filamentating laser pulses

Flexible pressure sensors are promising for biomedical diagnosis and health monitoring, but most of such sensors meet with problems of one kind or another, such as counterfeit sensitivity, poor durability, expensive fabrication cost and trade-off between sensitivity and sensing range. Herein, a high-performance flexible pressure sensor microstructured with femtosecond filamentating pulses is assembled to realize robust physiological signal monitoring. The sensing mechanism is based on the change of contact resistance between the patterned silver conductive ink thin layer and the laser filament-microstructured polydimethylsiloxane film coated with single-walled carbon nanotubes. The sensor exhibits a maximum sensitivity of 0.266 kPa−1, a broad range of up to 160 kPa and an excellent stability. Benefiting from the aforementioned advantages, the sensor is used with success to detect a variety of human physiological signals, such as real-time artery pulse and throat muscle movement. Moreover, with the assistance of principle component analysis algorithm, it is demonstrated that the sensor can unambiguously distinguish different phonations, making it high potential for application in physiological analysis systems.

Flexible high-performance organic thin film transistors and PMOS inverters: Trap controlled grain boundaries and contact resistance effect in different channel length devices

Printed high-performance organic thin film transistors (OTFTs) are fabricated on flexible polyethylene naphthalate (PEN) substrate for low-voltage operation. Gate, source and drain electrodes are inkjet-printed using conductive silver ink, while chemical vapor deposition grown parylene is used as dielectric layer. We used a blend of 2,7-dihexyl-dithieno[2,3-d;2′,3′-d′]benzo[1,2-b;4,5-b′]dithiophene (DTBDT-C6) and polystyrene (PS), for active p-type organic semiconducting material, and deposited by a dispenser system to achieve 0.66 cm2/Vs mobility at VGS = −6 V. For a set of 30 OTFT devices, the uniformity in device characteristics is illustrated by plotting the histograms for on current, mobility, and threshold voltage (VTh). Mobility decrease for small channel length due to greater contribution of contact resistance, while negative VTh shift occurs because of the generation of hole traps at dielectric-semiconductor interface attributed to moisture present. Electron traps on grain boundaries of the active semiconducting layer causes positive shift in VTh. By using these high mobility OTFT devices, two different low-voltage operation PMOS (P-channel metal-oxide-semiconductor) inverters are fabricated for which high signal gain value of 24.86 is achieved at VDD = −5 V.

A preliminary study of printed electronics through flexography impression on flexible substrates

The work is framed within Printed Electronics, an emerging technology for the manufacture of electronic products. Among the different printing methods, the roll-to-roll flexography technique is used because it allows continuous manufacturing and high productivity at low cost. Apart from the process parameters, the ink and the substrate properties are some of the variables associated with the flexographic printing. Specifically, this study investigates the ink penetration, the print uniformity, the adhesion, the fastness, and the electrical behaviour of the same conductive silver ink printed on different flexible substrates through the flexography process. In addition to polymeric and siliconized paper substrates, which are typical used in printed electronics, two substrates were also chosen for the study: woven and nonwoven fabric. Optical, scanning electronic microscope (SEM), 4-point Kelvin and colour fastness to wash and rubbing analyses have been performed. The results concluded that, regarding the conductivity behaviour, porous substrates like textiles and nonwoven fabrics without pre and post treatments do not present acceptable results, whereas polymers or silicone papers do. Nevertheless, woven and nonwoven fabrics are a suitable early option regarding colour fastness to wash instead of thin polymeric and paper substrates that tear at the wash machine. A solution for an optimal printing on textiles would be the surface substrates pre-treatment by applying different chemical compounds that increase the adhesion of the ink on the fabric

Silver Inkjet-Printed Electrode on Paper for Electrochemical Sensing of Paraquat

The use of fully printed electrochemical devices has gained more attention for the monitoring of clinical, food, and environmental analytes due to their low cost, great reproducibility, and versatility characteristics, serving as an important technology for commercial application. Therefore, a paper-based inkjet-printed electrochemical system is proposed as a cost-effective analytical detection tool for paraquat. Chromatographic paper was used as the printing substrate due its sustainable and disposable characteristics, and an inkjet-printing system deposited the conductive silver ink with no further modification on the paper surface, providing a three-electrode system. The printed electrodes were characterized with scanning electron microscopy, cyclic voltammetry, and chronopotentiometry. The proposed sensor exhibited a large surface area, providing a powerful tool for paraquat detection due to its higher analytical signal. For the detection of paraquat, square-wave voltammetry was used, and the results showed a linear response range of 3.0–100 μM and a detection limit of 0.80 µM, along with the high repeatability and disposability of the sensor. The prepared sensors were also sufficiently selective against interference, and high accuracy (recovery range = 96.7–113%) was obtained when applied to samples (water, human serum, and orange juice), showing the promising applicability of fully printed electrodes for electrochemical monitoring.

Integrating digital light processing with direct ink writing for hybrid 3D printing of functional structures and devices

As an emerging branch of additive manufacturing, multi-material 3D printing has drawn tremendous attention as it offers more design flexibility that can combine materials with various mechanical, chemical, thermal-mechanical or electrical properties. However, low cost, high-speed, high-resolution, and versatile multi-material 3D printing methods are still lacking. In this paper, we present a new hybrid multi-material 3D printing system that consists of a top-down digital light processing (DLP) printing and a direct ink writing (DIW) printing to fabricate composite structures and unique devices in a single printing job. The vat photopolymerization-based DLP printing allows for high-speed and high-resolution printing of a material matrix with complex geometry. The material extrusion-based DIW printing enables the printing of functional material, including liquid crystal elastomers (LCEs) and conductive silver inks. With this hybrid 3D printing system, a wide choice of inks and resins can be used to print functional composites with tunable mechanical properties, enhanced interfacial bonding, and multifunctionality. We demonstrate that composites prototype, active soft robots, circuit-embedding architectures, and strain sensors can be successfully printed. This work provides a new and robust approach for 3D printing of multi-functional devices for broad applications in soft robotics, electronics, active metamaterials, and biomedical devices.

Ultrawideband inkjet‐printed monopole antennas for energy harvesting application

AbstractMultiple communication and identification systems are taking advantage of inkjet‐printing techniques for the production of flexible, low‐cost, and lightweight printed radiating elements. In this paper, we bring the advantages of inkjet printing to the design of efficient and low‐cost wideband radio‐frequency (RF) energy harvesters. We present the design, manufacturing, and measurement of two inkjet‐printed ultrawideband monopole antennas. Both elliptical and circular monopoles are printed with a silver conductive ink on a thin polyethylene terephthalate film that lays on a foam substrate. Measurements show that the antennas operate efficiently from 0.6 to 8 GHz, covering the most relevant power contributions coming from the radio spectrum. In addition, the antennas show omnidirectional characteristics, highly desirable for broad spatial coverage in RF energy harvesting.

Paint‐On Epidermal Electronics for On‐Demand Sensors and Circuits

AbstractWearable sensors continually evolve to become more epidermal‐like, yet still face challenges pertaining to conformability and reliance on wires and power sources. Herein, a nontoxic silver conductive ink made from children's school glue is used as a versatile medium for rapid, on‐demand wearable sensor development. This conductive ink can be painted directly onto the skin and to achieve dry electronics with maximal skin contact suitable for electrocardiogram use. Multilayer pressure sensors and near‐field communication (NFC) resonators manufactured using the silver ink demonstrate wireless and battery‐free capabilities for physiological monitoring purposes.

Fiber Bragg grating sensors for in-situ temperature measurement on bending a flexible planar supercapacitor

The state of charge (SoC) in a flexible planar supercapacitor is dependent both on in-situ temperature rise as well as its bending angle. Thus there is a need for measurement of rising in temperature of the supercapacitor on bending conditions. The present work demonstrates the applicability of fiber Bragg grating (FBG) sensors for in-situ temperature measurement on bending in flexible planar supercapacitors. For this purpose, two FBG sensors with diameter 125 μm and 40 μm were inserted into a flexible planar supercapacitor at a location away from the bending axis. The FBG with 40 μm diameter was coated with conductive silver ink to enhance the temperature sensitivity and the diameter of this FBG after coating was found to be 80 μm. The planar supercapacitor consisted of multi-walled carbon nanotube adsorbed on filter paper as electrodes and NH4CN as an electrolyte. The temperature and bend sensitivities for FBG with 125 μm diameter was found to be 10 pm/°C and 17 pm/° respectively whereas for the FBG with 80 μm diameter the temperature and bend sensitivities were 16 pm/°C and 21 pm/° respectively. The measurement resolution for temperature and bending angles were found to be 0.2 °C and 0.4°, respectively. Maximum measurement errors of 0.9 °C and 0.8° in the measurement range 0−70 °C and 0−50° respectively were found. The high sensitivity and resolution, along with low measurement error in in-situ temperature measurement on bending revealed that the proposed method was suitable for monitoring the SoC in flexible planar supercapacitors. The study, conducted on the variation of in-situ temperature rise on bending with specific capacitance and equivalent series resistance, opens up new possibility towards the development of supercapacitor temperature management systems for flexible planar supercapacitor.

Passivation capability of carbon black layers for screen-printed battery applications with Ag current collectors

Screen-printed thin-film batteries comprise current collectors typically realised with commercially available conductive silver inks primarily designed for non-critical printed electronics applications. The avoidance of electrochemical interaction of metallic silver with the respective battery chemistry requires printing of an additional passivation layer. The wide range of printing inks available makes it difficult for researchers to select and qualify battery specific inks that ensure a long-life cycle without limitation of relevant battery performance parameters. This study presents a novel method to quantify the passivation capability of carbon black passivation layers for silver current collectors in 6.0 M potassium hydroxide and 5.8 M zinc chloride aqueous electrolyte solutions. Cyclic voltammetry is used to determine possible electrochemical interaction of passivated current collectors with the electrolyte media which constitute battery performance degrading parasitic side reactions. An innovative approach based on Faraday’s law of electrolysis is presented to transform cyclic voltammogram curve progressions into comparable numerical values. The mathematical approach allows quantitative comparison of individually fabricated passivation layers with respect to their passivation capability instead of interpreting a large number of cyclic voltammograms.

Silver nanoparticle conductive inks: synthesis, characterization, and fabrication of inkjet-printed flexible electrodes

Flexible electronics can be developed with a low-cost and simple fabrication process while being environmentally friendly. Conductive silver inks have been the most applied material in flexible substrates. This study evaluated the performance of different conductive ink formulations using silver nanoparticles by studying the material properties, the inkjet printing process, and application based on electrical impedance spectroscopy using a buffer solution. Silver nanoparticles synthesis was carried out through chemical reduction of silver nitrate; then, seven conductive ink formulations were produced. Properties such as resistivity, viscosity, surface tension, adhesion, inkjet printability of the inks, and electrical impedance of the printed electrodes were investigated. Curing temperature directly influenced the electrical properties of the inks. The resistivity obtained varied from 3.3 × 100 to 5.6 × 10−06 Ω.cm. Viscosity ranged from 3.7 to 7.4 mPa.s, which is suitable for inkjet printing fabrication. By using a buffer solution as an analyte, the printed electrode pairs presented electrical impedance lower than 200 Ω for all the proposed designs, demonstrating the potential of the formulated inks for utilization in flexible electronic devices for biological sensing applications.

Mechanical and light resistance of flexographic conductive ink films intended for printed electronics

The objective of the research is to investigate the mechanical and light resistance of two most common water-based and solvent inks with electrical properties printed on a paper substrate with the use of flexographic laboratory devices. One of them is black carbon semi-conductive the other one silver and copper conductive ink. Different thicknesses of these inks are tested to light and rub resistance. The sheet conductance and sheet resistance of the ink layers exposed to destructive factors is presented.The innovation in this research is to compare the changes in the properties of these inks due to the aforementioned destructive factors. It is also shown how the ink film thickness impacts its conductive properties. Black carbon nanoparticle ink after being subjected to abrasion exhibits about 67% better electrical properties and 11 times as good colorimetric properties as ink based on silver and copper mixture. The light destructive agent of 36 h and the rub off process have a negligible impact on the colour changes of black carbon ink 1 and a noticeable impact on silver and copper ink 2. The innovative conclusion is that the sheet resistance parameter of both the inks tested increases due to artificial light ageing and the abrasion process.

A Polyimide Based Force Sensor Fabricated Using Additive Screen-Printing Process for Flexible Electronics

A flexible capacitive force sensor was developed for force sensing applications. The force sensor consists of two electrodes and a dielectric layer. The electrodes were fabricated by depositing conductive silver (Ag) ink on a flexible polyimide platform using screen-printing process. The dielectric layer was prepared by mixing the contents of polydimethylsiloxane (PDMS) (pre-polymer and curing agent) in a 16:1 ratio. Then the PDMS dielectric layer was sandwiched between the screen-printed Ag electrodes. The capability of the fabricated force sensor was investigated by recording its capacitive response for varying applied forces of 100 N. It was observed that the capacitance increased from 5.83 pF to 6.36 pF as the force was increased from 0 N (no load) to 100 N. A sensitivity and correlation coefficient of 0.081%N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and 0.998 were calculated for the force sensor. In addition, a response time and recovery time of 3.7 seconds and 5.7 seconds was measured for the fabricated force sensor. The relative humidity (% RH) tests performed from 20% RH to 80% RH, in steps of 20% RH, revealed that there was a minimal effect of RH on the base capacitance of the force sensor at room temperature.

Enhanced Hybrid Copper Conductive Ink for Low Power Selective Laser Sintering

Copper conductive ink has great potential as an electrode material for flexible electronics due to its low-cost relative to silver conductive ink while having comparable electrical conductivity. The process of fabricating anti-oxidation hybrid copper conductive ink, however, results in an increase of required sintering energy; a high sintering temperature is disadvantageous due to the possibility of thermally damaging the substrate. In this study, selective laser sintering of new hybrid ink compositions was investigated by varying laser intensities and comparatively analyzing the resulting electrical conductivity. Then, the thermal behavior of fabricated inks during the sintering process was studied using experimental and numerical approaches. A finite element model was developed to simulate the laser heat flux and irradiation paths on the ink. Finally, the obtained results of the thermal profile were verified experimentally.

3D Printed Fingernail Antennas for 5G Applications

3D printing of antennas on removable fingernail for on-body communications at microwave and millimetre waves is proposed. Aerosol Jet technology, a fine-feature material deposition solution, has been used to directly print microstrip patch antennas on an acrylonitrile butadiene styrene (ABS) removable finger nail substrate. Two antennas have been printed and assessed, one operating at 15 GHz and the other at 28 GHz. Nanoparticle conductive silver ink has been employed to create the microstrip patch antennas and corresponding transmission line using an Optomec machine. The inks are then cured using a PulseForge machine. A further copper layer is added to the millimeter wave antenna via an electroplating process. The antennas have been simulated and measured off-the-finger and on-the-finger. Simulated and measured reflection coefficients ( $S_{11}$ ) and radiation patterns are found to be in good agreement. The proposed on-body antennas can find application in the Internet of Things (IoT) where large amount of sensing data can be shared at the microwave and millimetre wave spectrum of future 5G communications. The removable finger nails could include other electronic devices such as on-body sensors, computational, storage and communication systems.

Fully inkjet-printed multilayered graphene-based flexible electrodes for repeatable electrochemical response.

Graphene has proven to be useful in biosensing applications. However, one of the main hurdles with printed graphene-based electrodes is achieving repeatable electrochemical performance from one printed electrode to another. We have developed a consistent fabrication process to control the sheet resistance of inkjet-printed graphene electrodes, thereby accomplishing repeatable electrochemical performance. Herein, we investigated the electrochemical properties of multilayered graphene (MLG) electrodes fully inkjet-printed (IJP) on flexible Kapton substrates. The electrodes were fabricated by inkjet printing three materials – (1) a conductive silver ink for electrical contact, (2) an insulating dielectric ink, and (3) MLG ink as the sensing material. The selected materials and fabrication methods provided great control over the ink rheology and material deposition, which enabled stable and repeatable electrochemical response: bending tests revealed the electrochemical behavior of these sensors remained consistent over 1000 bend cycles. Due to the abundance of structural defects (e.g., edge defects) present in the exfoliated graphene platelets, cyclic voltammetry (CV) of the graphene electrodes showed good electron transfer (k = 1.125 × 10−2 cm s−1) with a detection limit (0.01 mM) for the ferric/ferrocyanide redox couple, [Fe(CN)6]−3/−4, which is comparable or superior to modified graphene or graphene oxide-based sensors. Additionally, the potentiometric response of the electrodes displayed good sensitivity over the pH range of 4–10. Moreover, a fully IJP three-electrode device (MLG, platinum, and Ag/AgCl) also showed quasi-reversibility compared to a single IJP MLG electrode device. These findings demonstrate significant promise for scalable fabrication of a flexible, low cost, and fully-IJP wearable sensor system needed for space, military, and commercial biosensing applications.

Simple and green fabrication process of nano silver conductive ink and the application in frequency selective surface

A simple and green method for fabrication of nano silver conductive ink was developed for use in frequency selective surface (FSS). The hydrogen peroxide and ethyl cellulose were used as reducing agents and dispersants to synthesize silver nanoparticles (Ag NPs), and the ethyl cellulose was be used as binders of nano silver conductive ink eventually. The reaction byproducts of hydrogen peroxide are water and oxygen, the synthesized Ag NPs were be cleaned using purified water and alcohol without centrifugation and drying process. The conductive ink with 30 wt% silver content was formulated with the Ag NPs capped with ethyl cellulose, solvent and additive, the residual water and alcohol were be evaporated using vacuum distillation process. The prepared Ag NPs were characterized by SEM, XRD, TGA and FT-IR. The viscosity and surface tension of Ag NPs ink were tested, and the conductive ink was inkjet printed on Polyimide (PI) film to fabricate the FSS. The results showed the printed FSS had reflection resonances at 16.5 GHz and nulls deeper than the required −20 dB level, with depths of −32 dB.

Inkjet printing of particle-free silver conductive ink with low sintering temperature on flexible substrates

A facile synthesis method was developed to prepare the particle-free silver organic conductive ink, which contains silver-amide complex dispersed in glycol. Electrical and morphological characterizations were carried out to assess the performance of the ink. The patterns printed by a commercial inkjet printer (Epson R230) were treated at different temperatures and time to optimize the electrical and adhesion properties. The film sintered at 140 °C for 40 min showed a low electrical resistivity (about 5 μΩ∙cm) owing to the transformation of point contact to surface contact. These good performances indicated a penitential application in flexible electronics.

Mobile Digital TV Induction Array Four Helix Antenna

According to the performance requirements of the mobile digital TV system, the present paper originally combines polygonal four helix antenna, induction array antenna, dielectric constant gradient film, graphene conductive ink and nano silver conductive ink, designed a mobile digital TV inductive array four helix antenna. The result of test indicates that this antenna has completely covered the frequency band of the mobile digital TV system. This antenna has strong corrosion resistance and damage resistance, stable physical and mechanical performance and radiation performance, small size, thin thickness and large working bandwidth, so it has broad application prospects.

Reliability of printed wire bonds

Abstract Additive manufacturing is an emerging domain with numerous potential applications. The concept of those new processes offers many advantages such as design flexibility, truly 3D packages and low cost for customization. The aerosol jet printing could enable wire bonding-like techniques that are unachievable with round wires today, combined with serious advantages for high frequency applications. However, this new field is starting off with many challenges to address, with the reliability as a focal point. The focus of this study is the reliability of printed wire bonds. Polyimide and silver inks were printed using an aerosol jet system (OPTOMEC Aerosol Jet ® HD Decathlon™). The results are focusing on the reliability of the adhesion of polyimide ink (UTD-PI-AJ) in an ethanol-based diluent and a silver ink, the HPS-108AE1 from Novacentrix, on different surface types: silicon oxide, pure aluminum and gold (ENIG). The adhesion is first addressed by a qualitative tape test at room temperature. The test samples are then put into an environmental chamber for a Deep Thermal Cycling (DTC) stress. The samples cycled 1000 times between −20°C and 85°C. They were inspected for physical defects at 250, 500 and 750 cycles. The visual inspection for defects focuses on cracks and delamination. The printed wire bonds were simulated by printing polyimide ink into a gold plated flat ceramic substrate (28 LCC from Kyocera) and then printing conductive silver ink from opposite pin leads. A layer of polyimide ink was then added on top of the printed lines. Crossover lines were finally printed on top of the last polyimide layer, again from opposite pin leads, creating an array of superimposed printed wire bonds. The reliability of printed wire bonds is tested through a Highly Accelerated Stress Test (HAST, 110°C, 85%RH, 264h) under bias. The samples were inspected at 66h, 132h and 198h for visual defects such as cracks, delamination and silver electro-migration. Cross-sections were performed on samples before and after HAST. All defects were characterized regarding of their time and condition or appearance and of their dimensions.