Ag Ink Research Articles

Molecule bridged graphene/Ag for highly conductive ink

Printing is a method of additive manufacturing that can reduce material costs and environmental contamination during the fabrication process. Ag ink is commonly used in printed electronics, such as interconnects, inductors, and antennas. However, the high cost of noble Ag restricts its massive applications. To reduce the cost of the state-of-the-art Ag ink and realize large-scale manufacturing, we develop a molecule-bridged graphene/Ag (MB-G/A) composite to produce highly conductive and cost-effective paper-based electronics. Graphene can be used to substitute part of Ag nanoparticles to reduce costs, form a conducive percolation network, and retain a reasonable level of conductivity. We adopt cysteamine as a molecular linker, because it anchors on the surface of graphene via the diazonium reaction. Additionally, the thiol functional group on the other end of cysteamine can bond to a Ag atom, forming a molecular bridge between graphene and Ag and promoting electron transport between Ag and graphene. As a result, the maximum conductivity of MB-G/A inks can reach 2.0 × 105 S m−1, enabling their successful application in various printable electronics. In addition, the optimum MB-G/A ink costs less than half as much as pure Ag inks, showing the great potential of MB-G/A ink in commercial electronic devices.

Resistivity study of inkjet-printed structures and electrical interfacing on flexible substrates

Development and evaluation of electronics with printing techniques such as inkjet printing is currently an active subject of research with various outstanding results in sensing applications. Printing technologies have shown high efficiency and compatibility with various types of inks and substrates, enhancing the opportunity for scientific innovation and research in this field. The present work reports on the evaluation of the resistivity and the sheet resistance of inkjet-printed conductive commercial Ag-nanoparticle ink, graphene ink and a custom functionalized reduced graphene oxide ( f- rGO) ink on Kapton substrate using the Van-der-Pauw method. Two different approximations have been used to determine the sheet resistance (R s ) and the corresponding resistivity (ρ). The results showed differences in the extracted sheet resistance value, which emphasizes the importance of the adopted calculation method. Furthermore, in order to demonstrate the ability to fabricate printed structures with efficient electrical connection to external devices, we have evaluated standard methods for interfacing two inkjet-printed materials on Kapton substrate, namely: commercial Ag-nanoparticle ink and graphene ink. Two standard connection techniques implementing a 4-pin Flexible Printed Circuit (FPC) connector and an Amphenol Clincher connector were evaluated, along with a custom direct interconnection approach. Direct interconnection between Cu patterned tracks and printed structures attracts special interest because it addresses one of the main problems in printed electronics, which is the interfacing of the printed structure with other electronic or read-out components. Thus, the printed Ag-Graphene/Cu direct interconnection case was further investigated. Two-point [2p] and four-point [4p] measurements were performed in order to study the effect of the various probe locations of engagement to the extracted resistance. The results acquired for this interconnection method revealed the importance of the measurement probe location. To support these experimental results, FEA simulations were performed and the outcomes were consistent with the experimental findings. • Two approaches in the calculation process of sheet resistance, implementing Van-der-Pauw test structures showed the significance of the evaluation method to the results. • Application-level approaches for electrical interfacing, which utilize copper interconnections are presented and evaluated. • Both Ag ink and graphene ink can be inkjet-printed onto Kapton substrate and used as a reliableinterconnection method. • Direct interconnections revealed how the probe location, the contact resistance and the localization of electric field affect the measurement process.

Liquid Metal Fiber Mat as a Highly Stable Solid-State Junction for Inkjet-Printed Flexible Reference Electrodes.

An all-solid liquid-metal-fiber-mat-based membrane flexible reference electrode (LMFM-FRE) was developed by combining liquid metal eutectic gallium indium (EGaIn) and poly(styrene-block-butadiene-block-styrene) (SBS) as a liquid junction layer. Ag ink was printed and chlorinated by electroplating to form the AgCl layer. Then, agarose containing KCl was coated as the electrolyte layer, and LMFM was added as the liquid junction layer. The liquid junction layer can increase the hydrophobicity of the electrode surface, limit the loss of internal Cl-, and significantly improve the stability of the electrode. The potential fluctuation of LMFM-FRE does not exceed 1 mV within 1 h, and it is still the same after 1 month. In addition, its potential changes in ion species and concentration, pH value, and ambient light are small, and its cyclic voltammetry characteristics are consistent with the standard reference electrode. Even in the case of temperature change and mechanical deformation, the potential change of LMFM-FRE is minimal. In general, the materials used and fabrication by inkjet printing make it possible to manufacture the reference electrode on a large scale, which is particularly important in many electrochemical sensing fields.

The effect of PVAc in silver ink for adhesion and conductivity of conductive pattern

The adhesion with substrate and conductivity of silver (Ag) conductive pattern are critical for practical applications of flexible electronic devices. Polymer vinyl acetate (PVAc) as an important solvent in Ag ink might largely improve the conductive pattern's adhesion property. However, the addition of PVAc in Ag ink also result in decreasing the patterns conductivity to about 210 ± 2 μΩ cm after infrared sintering at air atmosphere. Here, we found a facial method to eliminate the effect of the addition of PVAc for Ag conductive pattern. In this method, the thickness of PVAc layer coated on Ag particles surface was decreased via a washing treatment by ethanol mixed with acetone. After post-sintering treatment of ethanol brushing, a stable and conductive pattern was achieved. Owing to these treatments, compared with the blank sample, the adhesion of patterns was improved by the scratch test with higher damage force from 1 to 3.8 N. Meanwhile, the resistivity of the formed Ag pattern gradually decreased to 22 ± 0.5 μΩ cm after post-sintering treatment for 50 times, and this value did not change after bending 6000 times. The mechanism was given and confirmed by energy dispersive spectroscopy (EDS) analysis, indicating that the residual organic coatings on patterns had been taken away by the evaporation of alcohol molecular. LEDs pasted in the electronic circuit of our university badge were illuminated, indicating their wide application in the field of flexible electronic devices.

Ionic solution-processable Ag nanostructures with tunable optical and electrical properties and strong adhesion to general substrates

We present a solution-processable Ag nanostructure (SPAN) fabrication protocol for thin metallic nanoarchitectures exhibiting tunable optical and electrical properties as well as strong adhesion to general materials, including transparent, flexible, and fabric substrates and graphene-coated surfaces. The SPAN film can be fabricated in a scalable, vacuum-free fashion simply by the coating of an ionic Ag ink with a subsequent thermal annealing process. Here, we systematically analyze and confirm that the Ag nanoclusters are reduced from Ag ions and evolve into the nanostructured film, where its morphology and porosity as well as its optical and electrical properties can be readily controlled by adjusting the initial Ag ink concentration and coating speed as well as the annealing temperature. Compared to the conventional vacuum-deposited Ag layer, the SPAN film shows generally improved adhesion regardless of the substrate material with the aid of additional organic binding. The SPAN architecture can thus be applied to further scalable and pragmatic frameworks such as the transparent and flexible conducting electrodes consisting of micromesh-patterned SPAN structures on transparent, flexible, and/or graphene-coated substrates and SPAN-interwoven electronic textiles. Many diverse material systems and functional architectures can benefit from SPAN, including but not limited to smart sensors, plasmonic structures, and printable and wearable devices.

Facile fabrication of stretchable photonic Ag nanostructures by soft-contact patterning of ionic Ag solution coatings

Abstract We describe a rapid and simple method to create Ag nanostructures by using direct mechanical patterning of ionic Ag ink coating under gentle pressure, then thermal annealing to reduce the ionic Ag ink to a metallic Ag layer. The ionic liquid-phase Ag coating is easily obtained by spin-coating ionic Ag ink that has appropriate Ag concentration and can be either printed or imprinted on the desired substrate by using a soft elastomer patterning mold, then reduced to the Ag nanostructure by subsequent thermal annealing. More specifically, we present two methods: transfer printing and soft nanoimprinting. In transfer printing, the ionic Ag ink is first inked onto the elastomer mold which then contacts the target substrate to transfer the Ag nanopattern. In soft nanoimprinting, the elastomer mold conducts soft imprinting to engineer the ionic Ag ink coating to the Ag nanostructure. We systematically investigate the optimal patterning conditions by controlling the initial Ag ink concentration and the coating, printing, imprinting, and annealing conditions, to derive Ag architecture that has tunable photonic functionality. As an example, we demonstrate polarization-sensitive reflective color filters that exploit shape-tunable Ag nanostructures fabricated by soft nanoimprinting using a controllably-stretched elastomer mold.

Development of a Novel Reverse Offset Printer Equipped with Double-Layer Blanket (DLB) for Micropattern Printing on 3D Curved Surfaces

The double-layer blanket (DLB) reverse offset is a newly designed printing process for patterning electronic circuits on a 3D curved surface. Unlike the existing reverse offset process, the DLB reverse offset utilizes an offset roll composed of two layers comprising polydimethylsiloxane (PDMS) and a thick, soft cushioned rubber to print microelectrode patterns and transparent electrodes on a curved surface. The optimal printing process was determined by adjusting the printing pressure and printing speed for horizontal and vertical micropatterns, based on which transparent electrodes with metal mesh and honeycomb structures with a line width of 30 μm and pitch of 600 μm with micropatterns ranging from 30 μm to 60 μm were printed on a curved surface. Ag ink was used, and the 3D curved surface indicated a print quality similar to that of the flat surface for both the vertical and horizontal patterns and transparent electrodes. The DLB reverse offset technique demonstrated the possibility of printing on a 3D curved surface and is expected to broaden the range of printed electronics to applications such as smart glasses and 3D shape sensors.

A silver-based ink for assessing low activity photocatalytic films

A new type of photocatalytic activity indicator ink, paii, is described based on the photocatalysed reduction of Ag ions to the metal, rather than that of a dye, such as resazurin, Rz. UVA irradiation of an Ag ink film coating on a photocatalytic surface produces a brown colouration due to Ag nanoparticle formation. The Ag ink is easy to make and provides a simple method for the rapid assessment of photocatalytic films, with the added advantage of being particularly sensitive to low activity photocatalytic materials, such as commercial self-cleaning tiles for which no International Standards Organisation, ISO, test exists, including a Rz paii ISO. A felt-tipped pen applied Ag ink film is used to identify the presence of activity in a wide range of different materials, including examples of commercial self-cleaning glass, tile, paint and plastic awning materials. Unlike its well-established Rz paii counterpart, the Ag ink is effective on very hydrophobic and delicate, i.e. easily removed, photocatalytic films. A protocol is employed for the Ag ink to provide a quantitative measure of photocatalytic activity on both a low activity photocatalytic material, i.e. a Hytect™ tile, and a moderately active, reference photocatalytic material, Activ™ glass. The potential of the Ag ink to aid research and development into, and quality assurance of, low activity photocatalytic films, and also help in identifying activity in films previously considered inert, is discussed briefly.

Fabrication of a Simple and Cheap Screen‐printed Silver/Silver Chloride (Ag/AgCl) Quasi‐reference Electrode

AbstractIn this work, a silver/silver chloride ink is fabricated using two steps. First the silver ink is prepare using silver, nail polish and acetone. Then the silver ink is painted in a paper substrate and a silver chloride layer is deposited using a bleach solution. The result is the silver/silver chloride conductive ink. The silver ink is cheap ($2.49/g), well‐dispersive and very easy to fabricate. The materials were characterized by SEM and XRD. The Ag ink showed the formation of a continuous network throughout the silver ink film with fewer agglomeration. The effective chlorination process was also observed in the Ag/AgCl characterization. Since the Ag/AgCl substrate will be used as a quasi‐reference electrode, it is important to investigate the electrical properties. The Ag ink showed an average ohmic resistance of 2.27 Ω. The addition of the AgCl layer decreases the conductivity, as expected. In summary, the Ag/Ag/Cl ink developed is simple, well‐dispersed, cheap and with good conductivity. Therefore, it can be used as a conductive ink in the fabrication of quasi‐reference electrodes.

Inkjet printing high performance flexible electrodes via a graphene decorated Ag ink

The preparation of printed flexible conductive electrodes is a very important step to realize low-cost preparation of ultra-low power consumption wearable electronic devices. Although silver ink has shown excellent conductivity and stability in the printed electronic devices, many critical issues including particle-to-particle disconnection under mechanical stress must be addressed before it is applied in the flexible field. Here, we have proposed a one-step in-situ synthesis of low-cost Ag ink doped with graphene. It is demonstrated the effectiveness of the printed Ag network embedded by graphene as flexible electrodes, and investigated their conductive, mechanical and microstructural properties. As a metal-based reinforcing material, graphene could improve the flexibility of the metal-based matrix through effects such as stress transfer, dislocation strengthening, and grain refinement, while maintaining their low resistance. In this work, the electrodes obtained from the functional material with graphene mass fraction of 6.7% exhibit a low resistivity of 4.81 × 10−7 Ω•m. Even after 100,000 cycles of bending cycles, the printed electrodes could almost still maintain the initial conductivity. The facile synthesis and good properties make the material have great application potential in wearable electronic devices.

Direct ink write printing of resistive-type humidity sensors

To practice the development of printed electronics, researchers need to have the access to dedicated printer of electronic materials. However, commercial printing machines require large capital investment. Direct ink write (DIW) printing on the other hand operates with single printing head and less complex system therefore is promising for tight budget projects. Herein, a DIW printing system was home-built by making modifications to a 3D printer with ready to use components. Direct pattering and minimal printing line width of 230 ± 10 µm are demonstrated using an all solution-based Ag ink. Resistive-type humidity sensors were fabricated with DIW printed Ag electrodes and poly (diallyl dimethyl ammonium chloride) (PDDA) sensing layer. Humidity sensing performance of the sensors were examined and by taking advantage the flexibility of printing deposition, DIW printing was used to make quick modification toward a partially covered sensor structure for improved performance. Sensing response of more than 99% was obtained from 10% RH to 90% RH. Smaller hysteresis of ±4.4% RH and faster response of 7 s for adsorption and 213 s for desorption were obtained with the partially covered sensor. DIW printing is found to be a useful tool for device prototyping and ink development of printed electronics.

Electrodeposition and Electroless Deposition for High Conductivity, High Resolution Aerosol Jet Printed Components

Aerosol jet printing (AJP) additive manufacturing is a technique capable of depositing a variety of materials with linewidths on the order of 10-50 mm. [1] These materials include polymers, metal nanoparticle inks, and ceramics. [2] Nanoparticle Ag inks have been widely used for printing of conductive structures because of their low cost and ease of printing. However, the maximum conductivity of these inks reported in the literature does not exceed around 25% of bulk.[3] Reducing the resistance of a printed part by increasing the number of layers decreases the resolution due to ink spreading. Alternatively, nanoparticle-free reactive inks can reach 60-70% of bulk Ag conductivity but require thermal treatments at 300oC that are incompatible with some substrate materials. [4] Here, we combine AJP with electrochemical deposition processes enabling the fabrication of electronic components with the high resolution of AJP and the higher conductivity parts typical of the electrodeposition. This hybrid process offers access to new materials for which no ink formulations exist but where electrochemical deposition processes including both electroless deposition and electroplating are readily available. Recently we have demonstrated the resistance of printed inductors can be reduced by a factor of 35-45x by Cu electrodeposition from an acid Cu plating bath. [1]Herein, we report on a hybrid approach where aerosol jet printing of nanoparticle Ag ink (UTDots, Ag40X) is used to template a seed layer followed by the electroless and/or electrodeposition of a high conductivity metal. This technique is particularly attractive in the modification of long length printed inductor spirals. Here an Ohmic drop between the interior and exterior of the spirals creates a non-uniform current distribution across the length of the component. Electroless deposition prior to electrodeposition can reinforce the conductance of the part by decreasing this Ohmic loss. An electroless deposition process using a Circuposit Cu solution reduces a spiral inductor’s DC resistance from > 2 kΩ to 105 Ω (Figure 1). The optimization of the hybrid electroless and electrodeposition process parameters for maximizing conductivity, inductance, tolerance of temperature cycling, and uniformity of deposition will also be presented. Acknowledgments SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2021-4056 A

Printed and Laser-Scribed Stretchable Conductors on Thin Elastomers for Soft and Wearable Electronics

As printed electronics is evolving toward applications in biosensing and wearables, the need for novel routes to fabricate flat, lightweight, stretchable conductors is increasing in importance but still represents a challenge, limiting the actual adoption of ultrathin wearable devices in real scenarios. A suitable strategy for creating soft yet robust and stretchable interconnections in the aforementioned technological applications is to use print-related techniques to pattern conductors on top of elastomer substrates. In this study, some thin elastomeric sheets—two forms of medical grade thermoplastic polyurethanes and a medical grade silicone—are considered as suitable substrates. Their mechanical, surface, and moisture barrier properties—relevant for their application in soft and wearable electronics—are first investigated. Various approaches are tested to pattern conductors, based on screen printing of 1) conducting polymer [poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)] or 2) stretchable Ag ink and 3) laser scribing of laser-induced graphene (LIG). The electromechanical properties of these materials are investigated by means of tensile testing and concurrent electrical measurements up to a maximum strain of 100%. Performance of the different stretchable conductors is compared and rationalized, evidencing the differences in onset and propagation of failure. LIG conductors embedded into MPU have shown the best compromise in terms of electromechanical performance for the envisioned application. LIG/MPU showed full recovery of initial resistance after multiple stretching up to 30% strain and recovery of functionality even after 100% stretch. These have been then used in a proof-of-concept application as connectors for a wearable tattoo biosensor, providing a stable and lightweight connection for external wiring.

3-D printed electrode integrated sensing chip and a PoC device for enzyme free electrochemical detection of blood urea

Herein we report a novel electrochemical sensing chip and a point-of-care device (PoC) for enzyme-free electrochemical detection of urea in human blood. The electrochemical sensing chip was developed by 3-D printing of conductive Ag ink and subsequent electrodeposition of AuNP-rGO nanocomposite. Material characterization of the sensing chip was conducted to find a plausible mechanism for the electrochemical reaction with urea. Subsequently, the response with varying concentrations of urea in solution and human blood samples was tested. High peak response current (~5 times than that of the highest reported value), low impedance, rapid sensor fabrication procedure, high selectivity towards urea, excellent linear response (R2 = 0.99), high sensitivity of 183 μA mM−1 cm−2, the fast response indicated by high diffusion coefficient, the limit of detection of 0.1 µM, tested shelf life of more than 6 months and recovery rate of >99% ensured the application of the developed sensor chip towards PoC urea detection test kit. A PoC device housing an electronic circuitry following the principles of linear sweep voltammetry and compatible with a sensing chip was developed. A maximum percentage error of 4.86% and maximum RSD of 3.63% confirmed the use of the PoC device for rapid urea measurements in human blood.

An Innovative Immunoanalysis Strategy towards Sensitive Recognition of PSA Biomarker in Human Plasma Samples Using Flexible and Portable Paper Based Biosensor: A New Platform towards POC Detection of Cancer Biomarkers Using Integration of Pen-on Paper Technology with Immunoassays Methods

Background: The prostate-specific antigen (PSA) is one of the best markers for detecting prostate cancer. Rapid and real time recognition of PSA biomarker could be helpful in the early diagnosis and efficient treatment of prostate cancer. One of the usual methods to identify this biomarker is ELISA, which has a picomolar detection range but requires specialized personnel and also this technique is time-consuming and expensive. Methods: Cost-effective POC devices are great solutions because they are very cost-effective, sensitive and simple, do not require expert operators and have a high response time in a short time. With that in mind, in this work, a novel and simple label-free paper-based electrochemical immunosensor were designed by using conductive Ag-ink and designed directly by pen on paper technique on the surface of photographic paper, which is a suitable substrate for antibody immobilization, for rapid detection of PSA. Results: Based on the obtained results, under the optimum conditions, the synthesized Ag ink has a great substrate for antibody (Ab) and antigen (Ag) immobilization. The linear range was from 0.001 to 30 μg/L and the obtained low limite of quantification (LLOQ) was 0.001μg/L. This immunosensor also tested in human plasma samples, which had good analytical power. Conclusion: The proposed paper-based immunoassay could be a hopefully new and cheap tool for the diagnosis of other biomarkers.

An innovative flexible and portable DNA based biodevice towards sensitive identification of Haemophilus influenzae bacterial genome: A new platform for the rapid and low cost recognition of pathogenic bacteria using point of care (POC) analysis

Nowadays, different respiratory infections of Haemophilus Influenzae (H. influenzae) such as bronchitis, pneumonia, acute otitis media and sinusitis reveals the high demand for developing efficient, rapid and low-cost sensing platforms. In this concept, pDNA and cDNA were exploited in electrochemical biosensors for monitoring H. influenzae. Accordingly, the Ag ink and Au@Ag core–shell/GQDs nano-ink were synthesized and drawn on the surface of photographic paper for designing a three-electrode paper-based biodevice. The selectivity of the designed platform was evaluated by three mismatched. Under the optimal experimental conditions, due to the high affinity of cDNA toward pDNA, the fabricated electrochemical bioassay provided good selectivity and sensitivity for the monitoring of H. influenzae. The developed flexible sensor could detect cDNA with linear range and LLOQ (lower limit of quantitation) 100 ZM to 0.1 pM and 100 ZM, respectively. The main advantages of this paper-based DNA bio-electrochemical sensor include acceptable sensitivity, selectivity, easy and fast operation to clinical analysis and biomedicine.

Polymer-Embedded Silver Microgrids by Particle-Free Reactive Inks for Flexible High-Performance Transparent Conducting Electrodes

We report on the fabrication and characterization of polymer-embedded silver (Ag) microgrid structures using a particle-free reactive Ag ink for flexible high-performance transparent conductive ele...

Feature Size Control by Layer-by-Layer Printing and Non-wettable Patterns for Inkjet Printing of Micro Metal Electrode

The feature size and resolution of inkjet printing is limited by nozzle size, jetting volume and ink spreading. This study proposes a unique inkjet printing method for controlling feature sizes such as line width and thickness for the fabrication of mciro metal electrodes. To form the micro metal electrodes, we printed silver (Ag) ink inside a hydrophilic track formed by a printed non-wettable patterns. The minimum line width of the printed Ag could be reduced up to 18 μm by using the jetted ink droplet of 35 ± 4.2 μm diameter, which is twice the line width. To increase the thickness of the microelectrode, Ag ink was repeatedly printed layer-by-layer, and the thickness could be increased to 1 μm for an 18 μm width. After optimizing the printing conditions for a straight line, the fabrication of a micro-grid electrode was demonstrated, by first printing a horizontal electrode pattern, then a vertical electrode pattern was printed by repeating the proposed printing method. Also, we investigated the sheet resistance of the Ag grid-printed ITO-coated glass substrate by changing the grid space distance.

Tunable Reverse Offset Printing with a Stretchable Blanket for Fabricating Flexible Printed Electronics

Reverse offset printing (ROP) is receiving increasing attention as an emerging technology for printed electronics due to its rapid, environment‐friendly fabrication processes. A tunable ROP process is proposed by exploiting the controlled elastic deformation of a stretchable blanket. First, the flat elastomeric blanket is elastically stretched before coating with the printing ink. Next, Ag ink is coated on the surface of a supporting substrate and sequentially transferred to a prestrained elastomeric blanket. Second, the patterned cliché is rolled over the prestrained blanket surface by applying an optimized pressure for patterning. Finally, releasing the strain in the patterned elastomeric blanket leads to a pattern deformation on pitch and sizes. A decrease in the line width and pitch is demonstrated using a tunable ROP process with a stretchable blanket. This unique tunable printing process offers the capability of low‐cost fabrication of various microstructures from a single cliché using simple mechanical stretching and releasing.

Toward the Use of Temporary Tattoo Electrodes for Impedancemetric Respiration Monitoring and Other Electrophysiological Recordings on Skin.

The development of dry, ultra-conformable and unperceivable temporary tattoo electrodes (TTEs), based on the ink-jet printing of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) on top of commercially available temporary tattoo paper, has gained increasing attention as a new and promising technology for electrophysiological recordings on skin. In this work, we present a TTEs epidermal sensor for real time monitoring of respiration through transthoracic impedance measurements, exploiting a new design, based on the application of soft screen printed Ag ink and magnetic interlink, that guarantees a repositionable, long-term stable and robust interconnection of TTEs with external “docking” devices. The efficiency of the TTE and the proposed interconnection strategy under stretching (up to 10%) and over time (up to 96 h) has been verified on a dedicated experimental setup and on humans, fulfilling the proposed specific application of transthoracic impedance measurements. The proposed approach makes this technology suitable for large-scale production and suitable not only for the specific use case presented, but also for real time monitoring of different bio-electric signals, as demonstrated through specific proof of concept demonstrators.