Ag Ink Research Articles

Practical SERS Substrates by Spray Coating of Silver Solutions for Deep Learning-Assisted Sensitive Antigen Identification

Surface-enhanced Raman spectroscopy (SERS) has long been recognized for its rapid and sensitive detection capabilities; however, challenges persist in practical fabrication of the substrates and interpreting complex data. Herein, we propose a deep learning (DL) assisted SERS approach to enable rapid and sensitive detection of analytes on a practical yet highly effective substrates prepared by direct spray-coating of a nanoparticle-free true solution of a reactive Ag ink and on-site thermal annealing mediated generation of nanostructures. This design ensured homogeneous distribution of Ag nanostructures throughout the entire substrate, significantly increasing the number of hotspots and enhancing the Raman signals, thereby achieving an impressive analytical enhancement factor of ~1010 in a reproducible and consistent manner. The diagnostic utility of this platform was demonstrated by detecting the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein in both buffer and saliva, with detection limits of 74.3pg/mL and 7.43ng/mL, respectively. The DL-assisted SERS not only accurately identified the presence or absence of viral antigen, but also automatically quantified the viral load. This automatic identification achieved an outstanding accuracy of ~99.9%, highlighting the exceptional performance of the proposed platform. This simple, cost-effective, scalable, and ultra-sensitive DL-assisted SERS platform offers significant opportunities for early and precise detection in a range of analytical scenarios.

Compliant Interconnects Based on Single Micrometer-sized Metal-Coated Polymer Spheres.

The rapid evolution of multifunctional electronics necessitates interconnection technologies appropriate for large dies with high-density and/or ultrafine pitch input/output pins. Existing technologies face numerous challenges, including demands for bonding equipment that can deliver extremely high force as well as thermo-mechanical stresses induced in the assembled packages due to mismatched thermal expansion of materials involved. This study proposes an approach to compliant interconnects comprising single micrometer-sized metal-coated polymer spheres, being joined to mating electrodes by sintering of Ag nano ink at low temperature (140 °C) and low pressure (∼15 mN/particle). Such an interconnection technology is expected to enhance the thermo-mechanical robustness of the assembled packages as well as be capable of high-density, ultrafine pitch interconnects. Our approach demonstrates control over conductive particles during assembly, achieving a 98% success rate in individual interconnects with a single captured particle. The use of sintered Ag not only secures free-standing particles on electrical pads (with an adhesion force above 2 μN) but also results in a 15% reduction in interconnect resistance, with measured resistance as low as 0.5 Ω, compared to interconnects without Ag ink. This method presents an alternative to metallurgical joints, particularly suited for high-density, ultrafine pitch applications, offering low bonding pressure and temperature, along with improved interconnect compliance to enhance the thermo-mechanical robustness of the packages.

Simple Isopropanol-Assisted Direct Soft Imprint Lithography for Residue-Free Microstructure Patterning.

A direct soft imprint lithography was proposed to realize the direct fabrication of residue-free, well-shaped functional patterns through a single step. This imprint method requires only a simply prepared isopropanol-treated polydimethylsiloxane (PDMS) stamp without any additional resists. Residue-free Ag patterns were successfully fabricated on different substrates by directly imprinting the Ag ink with the isopropanol-treated PDMS stamp. Furthermore, the coffee-ring effect of the imprinting Ag patterns can be eliminated by optimizing the imprinting time, isopropanol-treating time, and imprinting temperatures. Studies show that the residual Ag ink in the contact region can be absorbed by the isopropanol-treated PDMS stamp due to the "like dissolves like" principle. Finally, this method was employed to fabricate the Ag electrodes for the thin-film transistors, attaining a mobility of ∼8 cm2 V-1 s-1, which is comparable to those with vacuum-processed electrodes. This process provides a simple, low-cost, residue-free, coffee-ring-free, and fast patterning method in the field of microelectronics.

A vibrating membrane ejector for direct ink writing of printed electronics

Direct ink writing (DIW) represents a technical branch of additive manufacturing technology, particularly suitable for prototyping or small-batch printing production of printed electronic components. However, the existing print heads required for near or sub-100 μm line width are quite sophisticated, limiting the accessibility and application of the DIW method. This paper reports the use of the vibrating membrane ejector (VME) as a new option for the print head of DIW. The structure of the VME-based print head was specially designed for this purpose. Finite element modeling and analysis of the VME’s vibration characteristics were performed to provide insights into the ejection conditions and behaviors. The factors influencing the size of printed structures were identified and analyzed through the printing of a metal–organic complex silver (Ag) ink. After optimizing several operational parameters to limit the spreading effects and suppress the satellite droplets, the DIW printed line width has reached about 100 μm. The effectiveness of the VME-based print head was further demonstrated through the DIW fabrication of interdigitated electrodes and microstrip transmission lines. This highlights the versatility of the VME-based print head as a practical tool for device prototyping and ink development in the field of printed electronics.

Piezo inkjet formation of Ag nanoparticles from microdots arrays for surface plasmonic resonance

The study aims to explore a novel approach for fabricating plasmonic nanostructures to enhance the optical properties and performance of various optoelectronic devices. The research begins by employing a piezo-inkjet printing technique to deposit drops containing Ag nanoparticles (NPs) onto a glass substrate at a predefined equidistance, with the goal of obtaining arrays of Ag microdots (Ag-µdots) on the glass substrate. This process is followed by a thermal annealing treatment. The printing parameters are first optimized to achieve uniform deposition of different sizes of Ag-µdots arrays by controlling the number of Ag ink drops. Subsequently, the printed arrays undergo thermal annealing at various temperatures in air for 60 min, enabling precise and uniform control over nanoparticle formation. The printed Ag nanoparticles are characterized using field emission scanning electron microscopy and atomic force microscopy to analyze their morphological features, ensuring their suitability for plasmonic applications. UV–Vis spectrophotometry is employed to investigate the enhanced surface-plasmonic-resonance properties of the printed AgNPs. Measurements confirm that the equidistant arrays of AgNPs obtained from annealing Ag microdots exhibit enhanced light-matter interaction, leading to a surface plasmon resonance response dependent on the Ag NPs’ specific surface area. These enhanced surface plasmonic resonances open avenues for developing cutting-edge optoelectronic devices that leverage the benefits of plasmonic nanostructures, thereby enabling new opportunities for future technological developments across various fields.

Wearable patterned single electrode-based triboelectric nanogenerator for peak-encoded interface

Advancement in human-machine interface (HMI) is indispensable for development of virtual/augmented reality, robotics control, and artificial intelligence (AI). However, there lack a simple facile electronics to achieve accurate finger motion recognition and remote robot control through simple signal processing. Herein, a wearable patterned single electrode-based triboelectric nanogenerator (PS-TENG) based on regenerated silk film (rSF) is developed for peak-encoded interface, which can accurately identify the handwritten numbers or letters. The patterned single electrode, composed of nine units with five different patterns, is successfully constructed by ink-jet printing Ag inks on the rSF. When handwriting on the PS-TENG, the generated output voltage with different peak amplitude can be transformed into a peak spectrum with spatial information. Handwriting numbers or letters can be accurately identified through simple digitization data processing of the peak-encoded spectrum without complex algorithms. Furthermore, the PS-TENG as peak-encoded interface enables precise game play, accurate pattern lock, and wireless robot control. Importantly, based on relative amplitude of output signals, the peak-encoded code is regardless of factors including absolute amplitude of output signals, sliding speed and environmental humidity. Consequently, the PS-TENG, characterized by self-powered feature, simple structure and straightforward signal processing, demonstrates remarkable identification accuracy of handwritten numbers and letters through decoding unique and stable peak spectrum, which would have great potential in the field of virtual control panels, HMI and AI.

Metal-Complex Inks for Lower Cost and Improved Passivation for Silicon Photovoltaic Metallization

This contribution introduces the silicon PV community to screen-printable metal-complex inks that potentially will reduce Ag usage in Si PV metallization to one-quarter and costs to one-third that of traditional particle-based pastes while also improving passivation. Metal-complex inks are formulated using a Tollen’s reaction to produce inks with a high percentage of diamminesilver (I) cations (22 wt %) in a solution of acetate and formate anions. When printed and dried, labile ammonia ligands evaporate, leaving behind silver cations which, when reduced by formate anions and acetic acid, plate out silver and silver acetate. When annealed to just 300 °C a dense metallic silver film forms with excellent conductivity, and adhesion to silicon. When compared to traditional particle-based screen-printing pastes, the metal-complex inks are much denser, have higher conductivity, use less Ag, and are a fraction of the cost. Importantly, the inks anneal from 90 – 450 °C allowing for improved passivation schemes compared with fired SiNx. This contribution highlights first experiments on the improved passivation of metallized poly-Si/SiO2 passivated contacts using metal-complex Ag inks.

Intense pulsed light annealing of solution-based indium–gallium–zinc–oxide semiconductors with printed Ag source and drain electrodes for bottom gate thin film transistors

In this study, an intense pulsed light (IPL) annealing process for a printed multi-layered indium–gallium–zinc–oxide (IGZO) and silver (Ag) electrode structure was developed for a high performance all-printed inorganic thin film transistor (TFT). Through a solution process using IGZO precursor and Ag ink, the bottom gate structure TFT was fabricated. The spin coating method was used to form the IGZO semiconductor layer on a heavily-doped silicon wafer covered with thermally grown silicon dioxide. The annealing process of the IGZO layer utilized an optimized IPL irradiation process. The Ag inks were printed on the IGZO layer by screen printing to form the source and drain (S/D) pattern. This S/D pattern was dried by near infrared radiation (NIR) and the dried S/D pattern was sintered with intense pulsed light by varying the irradiation energy. The performances of the all-printed TFT such as the field effect mobility and on–off ratio electrical transfer properties were measured by a parameter analyzer. The interfacial analysis including the contact resistance and cross-sectional microstructure analysis is essential because diffusion phenomenon can occur during the annealing and sintering process. Consequently, this TFT device showed noteworthy performance (field effect mobility: 7.96 cm2/V s, on/off ratio: 107). This is similar performance compared to a conventional TFT, which is expected to open a new path in the printed metal oxide-based TFT field.

Ultralight Ag-grid current collector enabled by screen printing Ag ink on Cu foil as efficient deposition-inducing layer for dendrite-free lithium metal batteries

An ultralight deposition-inducing layer consisting of a grid-like Ag pattern on Cu foil was designed and fabricated by using a scalable screen-printing technique to guide a uniform lithium-plating behavior.

A fully printed sensor with optical readout for real-time flow monitoring

In recent years, there has been a growing interest in the development of flexible thermal flow sensing devices due to their wide-ranging applications. In this study, we present the fabrication of a screen-printed flow sensor with optical readout on a 125 μm polyethylene terephthalate substrate in a three-layer configuration. The device comprises electrodes made from a commercial silver (Ag) ink, a heating area using a commercial carbon ink, and a thermochromic (TC) layer employing a commercial ink with a standard activation temperature of 31 °C. We designed a specialized experimental setup to evaluate the performance of the optical flow sensor under static and dynamic conditions. To analyze the device’s thermal response and performance across various flow conditions, we utilized a combination of electrical measurements and infrared (IR)-optical imaging techniques. The all-printed device operates on the basis of a thermodynamic cycle frequency, which activates the TC ink, causing it to blink at a frequency related to the flow passing over the sensor. The results of our preliminary testing are highly promising, as the sensor successfully demonstrated a clear relationship between flow and optical duty cycle. This innovative device offers a contactless, low-cost, easy-to-use flow detection method and holds significant potential for various practical applications.

Demonstration of a roll-to-roll-configurable, all-solution-based progressive assembly of flexible transducer devices consisting of functional nanowires on micropatterned electrodes

We demonstrate continuous fabrication of flexible transducer devices consisting of interdigitated (IDT) Ag microelectrodes interconnected by ZnO nanowires (ZNWs), created via serially connected solution-processable micro- and nanofabrication processes. On an Ag layer obtainable from the mild thermal reduction of an ionic Ag ink coating, the roll-to-roll-driven photolithography process [termed photo roll lithography (PRL)] followed by wet-etching can be applied to continuously define the IDT microelectrode structure. Conformal ZNWs can then be grown selectively on the Ag electrodes to interconnect them via an Ag-mediated hydrothermal ZNW growth that does not require high-temperature seed sintering. Given that all of these constitutive processes are vacuum-free and solution-processable at a low temperature, and are compatible with continuous processing onto flexible substrates, they can be eventually configured into the roll-to-roll-processable progressive assembly. Through parametric optimizations of processes consisting of the roll-to-roll-configurable, solution-based progressive assembly of nanostructures (ROLSPAN), a flexible transducer consisting of ZNW-interconnected, PRL-ed IDT Ag electrodes can be developed. This flexible architecture faithfully performs UV sensing as well as optoelectronic transduction. The ROLSPAN concept along with its specific applicability to flexible devices may inspire many diverse functional systems requiring high-throughput low-temperature fabrication over large-area flexible substrates.

Synthesized silver nanoparticles decorated reduced graphene oxide/silver ink for aerosol jet printed conformal temperature sensor with a wide sensing range and excellent stability

Three-dimensional (3D) conformal printing of temperature sensors with a wide sensing range and high stability requires the potential printable material with excellent functionality and printability. Herein, a high-performance silver nanoparticles (Ag NPs) decorated reduced graphene oxide (RGO)/Ag (ADR/Ag) ink with low viscosity was synthesized for aerosol jet printing (AJP). Ag ions are electrostatically adsorbed on the graphene oxide (GO) surface, and Ag NPs (∼10 nm) were attached onto the RGO surface by in-situ liquid-phase reduction. The ADR nanoflakes were mixed with commercial Ag NPs ink, high resolution patterns with ink stream widths down to 10 μm are printed, and ADR/Ag-0.8% ink shows excellent low-temperature sintering capability and flexibility, and the resistivity of the printed traces is 9.79 × 10−5 Ω m after 1 h sintering at a relatively low temperature (75 °C). The resistance negligibly increases by only 5% after 1000 bending cycles, which is about 7 times lower compared to the pure Ag traces. Furthermore, we achieve the 3D printing of a conformal temperature sensor with a sensitivity range of (1.162–1.519) × 10−3/°C in the broad sensing range of 0–200 °C. These findings shed light on the additive manufacturing of high-performance conformal electronics using the emerging AJP technology.

Electrical Conductivity and Photodetection in 3D‐Printed Nanoporous Structures via Solution‐Processed Functional Materials

Abstract3D‐printed conductive structures are highly attractive due to their great potential for customizable electronic devices. While the traditional 3D printing of metal requires high temperatures to sinter metal powders or polymer/metal composites, low or room temperature processes will be advantageous to enable multi‐material deposition and integration of optoelectronic applications. Herein, digital light processing technology and inkjet printing are combined as an effective strategy to fabricate customized 3D conductive structures. In this approach, a 3D‐printed nanoporous (NPo) polymeric material is used as a substrate onto which a nanoparticle‐based Ag ink is printed. SEM and X‐ray nano computed tomography (nanoCT) measurements show that the porous morphology of the pristine NPo is retained after deposition and annealing of the Ag ink. By optimizing the deposition conditions, conductive structures with sheet resistance <2 Ω sq−1 are achieved when annealing at temperatures as low as 100 °C. Finally, the integration of an inkjet‐printed photodetector is investigated based on an organic semiconductor active layer onto the NPo substrate. Thus, the potential of this approach is demonstrated for the additive manufacturing of functional 3D‐printed optoelectronic devices.

Graphene-black phosphorus printed photodetectors

Layered materials (LMs) produced by liquid phase exfoliation (LPE) can be used as building blocks for optoelectronic applications. However, when compared with mechanically exfoliated flakes, or films prepared by chemical vapor deposition (CVD), LPE-based printed optoelectronic devices are limited by mobility, defects and trap states. Here, we present a scalable fabrication technique combining CVD with LPE LMs to overcome such limitations. We use black phosphorus inks, inkjet-printed on graphene on Si/SiO2, patterned by inkjet printing based lithography, and source and drain electrodes printed with an Ag ink, to prepare photodetectors (PDs). These have an external responsivity (R ext)∼337 A W−1 at 488 nm, and operate from visible (∼488 nm) to short-wave infrared (∼2.7 µm, R 48 mA W−1). We also use this approach to fabricate flexible PDs on polyester fabric, one of the most common used in textiles, achieving R 6 mA W−1 at 488 nm for an operating voltage of 1 V. Thus, our combination of scalable CVD and LPE techniques via inkjet printing is promising for wearable and flexible applications.

Electrohydrodynamic Printing of Ultrafine and Highly Conductive Ag Electrodes for Various Flexible Electronics

AbstractSilver nanoparticle (AgNP) based inks are widely used in printed electronics to form conductive patterns. However, high resolution and high electrical conductivity are still hard to achieve at the same time for the patterning of AgNP‐based electrodes. Herein, Ag patterns with a high resolution of sub‐10 µm and a high conductivity are realized by the electrohydrodynamic (EHD) printing. The parameters including the composition of Ag ink, printing speed, voltage, and working height are carefully controlled to increase the resolution, and the process window of the cone jet mode is established. With the help of the finite element simulation, the generation mechanism of the Taylor cone is clarified. Ag electrodes with various patterns and shapes are easily produced, which exhibited excellent patterning qualities, such as superior uniformity and flatness, narrow spacing, and clear edge definition. Finally, flexible light‐emitting diode (LED) circuits, transparent heaters, and supercapacitors are fabricated by EHD printed Ag grid electrodes. These results indicate that this work provides a simple and scalable strategy for fabricating ordered metal conductive patterns in the emerging printed electronics.

Hydrothermal synthesis of zinc oxide/PEDOT:PSS composite for flexible temperature sensor application

A flexible and printable temperature sensor was proposed for a fast detection of temperature measurements. A hybrid composite of zinc oxide (ZnO) and a conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonicacid) (PEDOT:PSS) was utilized as the temperature-sensing layer. An interdigitated electrodes structure based on silver (Ag) ink was used to electrically connect the composite through a facile drop-casting technique. A standout aspect of this work is the presentation of ZnO/PEDOT:PSS as a temperature-sensing layer. The PEDOT:PSS flakes were connected by hydrothermally prepared ZnO nanorods, which increased the composite sheets’ electrical conductivity. The linearity, sensitivity, stability and dynamic response of the flexible sensor were examined from a temperature of 29 °C–60 °C. The sensor has high sensitivity of 1.06% °C−1 with response and recovery times of 5 s and 12.7 s, respectively. This work clearly demonstrates the potential of ZnO/PEDOT:PSS composite for flexible temperature sensor and adds to the rapidly expanding field of personalized mobile healthcare.

Non-enzymatic glucose detection using nanocomposite decorated Cellulose-Based field effect transistor - a green electronics approach

Cellulose portrays suitable substrate material for biodegradable, cheaper, and sustainable electronic devices making it an alternative to traditional silicon/plastic materials. Additionally, field-effect transistors (FET) engross huge demand in biosensing applications owing to high amplification factors and work like transducers. Herein, fabrication, and the applicability of an eco-friendly, flexible, nanocomposite-decorated cellulose-based paper FET (PFET) chip, are demonstrated. Having cellulose as a dielectric as well as an active channel layer for depositing nanocomposite materials, and electrodes made of silver (Ag) ink, the as-fabricated PFET brings the concept of green electronics. The device exhibited good electrical and electronic behaviour having high electron and hole mobility (µe and µh) 3641 cm2V-1S-1 and 2436 cm2V-1S-1 in the absence and 8823 cm2V-1S-1 and 9116 cm2V-1S-1 respectively in the presence of glucose. Moreover, when tested for non-enzymatic glucose sensing under physiological pH conditions, a linear range from 0.1 mM to 5 mM with a low limit of detection (LOD) of 3 µM was observed. Finally, with satisfactory results, we proved the practical applicability of low-voltage PFET biosensors by measuring the glucose content in commercially available energy drinks and artificial urine samples. Hence, we developed a high-performance PFET chip utilising the circular economy concept with an optimised device structure and sensing techniques. We envisage that the device could enable real-time monitoring of glucose levels in commercially available drinks and diabetic urine samples.

Environmentally friendlier wireless energy power systems: The coil on a paper approach

Paper is ubiquitous in everyday life and a low-cost environmentally friendly material. Thus, the printing of advanced conductive/magnetic nanomaterials on paper will allow the scalable production of flexible smart electronics, including energy-storage devices, sensors, inductors or antennas, among others, contributing towards more sustainable electronics. Particularly, wireless charging technologies are becoming essential for internet-of-things (IoT)-related electronic devices due to the ever-decreasing dimensions of portable/mobile devices that limit the quantity of energy that can be stored. Here, screen-printed paper-based coils and inductors operating on the 1–20 MHz range are presented based on Poly(vynil alcohol)/Fe3O4 and Ag inks. The ability of the printed cores and inductors to be incorporated on flexible wireless power transfer modules (WPTM) is technologically demonstrated by wireless powering light-emitting diodes (LEDs). The achieved induction efficiency of 94% is the highest reported on printed and flexible WPTM. The printed coils are also characterized by mechanical, hydrophobic and electrical properties that are suitable for IoT and industry 4.0 applications.

Ultrashort laser sintering of printed silver nanoparticles on thin, flexible, and porous substrates

The fabrication of low-cost and mechanically robust flexible electronic patterns has increasingly gained attention due to their growing applications in flexible displays, touch screen panels, medical devices, and solar cells. Such applications require cost-effective deposition of metals in a well-controlled manner potentially using nanoparticles (NPs). The presence of solvent and precursors in NP based inks impacts the electrical conductivity of the printed pattern and a post-processing heating step is typically performed to restore the electrical properties and structure of the material. We report printing with picolitre droplet volumes of silver (Ag) NPs on flexible substrates using an acoustic microdroplet dispenser. The low-cost, controlled deposition of Ag ink is performed at room temperature on photopaper, polyimide and clear polyimide substrates. A localized, ultrashort pulsed laser with minimal heat affected zone is employed to sinter printed Ag patterns. For comparison, oven sintering is performed, and the results are analysed with scanning electron microscopy, four-point probe and Hall measurements. The femtosecond laser sintering revealed highly organized, connected nanostructure that is not achievable with oven heating. A significant decrease in sheet resistance, up to 93% in Ag NPs on clear polyimide confirms the laser sintering improves the connectivity of the printed film and as a result, the electrical properties are enhanced. The surface morphology attained by the laser sintering process is interpreted to be due to a joining of NPs as a result of a solid-state diffusion process in the near surface region of NPs.

Lamination of inkjet-printed Ag electrodes for highly patternable and customizable polymer light-emitting diodes

Inkjet printing that ensures superior patternability and customizability can be fully exploited as top electrodes in thin-film-based light-emitting devices. However, direct inkjet printing onto multi-layered thin films severely damages the underlying functional layers due to intermixing with the ink solvents, resulting in poor device efficiencies. Here, we report a lamination of inkjet-printed Ag electrodes as a top cathode for polymer light-emitting diodes (PLEDs). The organometallic Ag ink was printed on surface-modified elastomers with stable wettability, and drop spacing was further optimized for low surface roughness. The lamination of Ag cathodes establishes intimate contact between the electrodes and the functional layers, allowing light emission of PLEDs along the printed patterns. Furthermore, additional heat treatment improves the electron injection, resulting in a reduction of turn-on voltage and higher current/power efficiencies. To illustrate the practicability of our laminated PLEDs, we demonstrate passive-matrix driven PLEDs with all-inkjet-printed electrodes by laminating the top cathode arrays crossing the bottom inkjet-printed anodes.