Inkjet Printing Technique Research Articles

The ink-jet printed flexible interdigital capacitors: manufacturing and ageing tests

Correct operation of electronic circuits (including those made with the ink-jet printing technique) requires the electrical parameters of the structures to be constant or to be changeable, but in a predictable way. Due to that, the flexible, ink-jet printed interdigital capacitors (IDSs) were made and then tested in various conditions. We used the conductive silver-based Amepox AX JP-60n ink. As a substrate, we chose the transparent, flexible Melinex OD foil with a thickness of 125 µm. The IDCs were designed and their capacitances were simulated using Comsol Multiphysics Software. Then the test structures were fabricated by the ink-jet printing process using Dimatix DMP 2831 printer. The printed structures were subjected to environmental exposures in a climate chamber to check the influence of temperature and humidity on the tested samples. The IDCs were also subjected to cyclic bending and straightening tests to analyze the outflow of tensile forces on the printed structures, which are exposed to the common factors, that could diminish the quality of the printed and flexible devices. Due to the small capacitance values of the designed and made IDSs, the measurements showed the key importance of the measuring table on which flexible substrates with IDC capacitors were placed for their capacitance value. Performed tests also demonstrated that in most cases, the capacitors are characterized by an increase in capacitance by a few to a dozen or so % after the ageing tests. Obtained results could be a good groundwork for further research, that will include ways of preventing the creation of discontinuities—or minimizing their impact on the printed device performance.

Printed Devices for Wearable Biosensors: Laboratory to Emerging Markets

Advances in flexible electrochemical sensors have opened up opportunities for various applications, such as biomedical and fitness monitoring. This brief review explores the key advancements in printed wearable electrochemical sensing systems, including an analysis of literature trends, printing strategies (flexographic, screen, and inkjet printing techniques), recent applications of printed wearable biosensors (epidermal sensing films and patches, textile platforms, and biofuel cell energy devices), their relative merits, and perspectives on this emerging technology. This article also provides an overview of sensing systems and concludes with a synopsis of the market drivers for printed and flexible sensors.

Inkjet‐Printed and Nanopatterned Photonic Phosphor Motifs with Strongly Polarized and Directional Light‐Emission

AbstractHerein a versatile and scalable method to prepare periodically corrugated nanophosphor surface patterns displaying strongly polarized and directional visible light emission is demonstrated. A combination of inkjet printing and soft lithography techniques is employed to obtain arbitrarily shaped light emitting motifs. Such predesigned luminescent drawings, in which the polarization and angular properties of the emitted light are determined and finely tuned through the surface relief, can be used as anti‐counterfeiting labels, as these two specific optical features provide additional means to identify any unauthorized or forged copy of the protected item. The potential of this approach is exemplified by processing a self‐standing photoluminescent quick response code whose emission is both polarized and directionally beamed. Physical insight of the mechanism behind the directional out‐coupled photoluminescence observed is provided by finite‐difference time‐domain calculations.

A Nonenzymatic Sensor Platform Fabricated by a Consumable Inkjet Printer

Inkjet printing has been shown to be a cost-effective technique for sensor fabrications. In this work, a nonenzymatic sensor platform capable of tunable sensing applications was designed and fabricated by a consumable inkjet printing technique. To establish the platform’s capability, a well-known and studied analyte, glucose, was used to demonstrate the proof of concept. The limit of detection, linear range, sensitivity, reproducibility, and selectivity of the sensor in the presence of several interfering species was comparable to or better than existing ones. This sensor platform has the potential for modifications for the detection of other analytes.

Electrohydrodynamic Printed Ultra-Micro AgNPs Thin Film Temperature Sensors Array for High-Resolution Sensing.

Current methods for thin film sensors preparation include screen printing, inkjet printing, and MEMS (microelectromechanical systems) techniques. However, their limitations in achieving sub-10 μm line widths hinder high-density sensors array fabrication. Electrohydrodynamic (EHD) printing is a promising alternative due to its ability to print multiple materials and multilayer structures with patterned films less than 10 μm width. In this paper, we innovatively proposed a method using only EHD printing to prepare ultra-micro thin film temperature sensors array. The sensitive layer of the four sensors was compactly integrated within an area measuring 450 μm × 450 μm, featuring a line width of less than 10 μm, and a film thickness ranging from 150 nm to 230 nm. The conductive network of silver nanoparticles exhibited a porosity of 0.86%. After a 17 h temperature-resistance test, significant differences in the performance of the four sensors were observed. Sensor 3 showcased relatively superior performance, boasting a fitted linearity of 0.99994 and a TCR of 937.8 ppm/°C within the temperature range of 20 °C to 120 °C. Moreover, after the 17 h test, a resistance change rate of 0.17% was recorded at 20 °C.

Low loading inkjet printed bifunctional electrodes for proton exchange membrane unitized regenerative fuel cells

Inkjet printing is evaluated as a feasible technique for unitized regenerative fuel cells (URFCs) electrode fabrication and to study the optimal ionomer and catalyst loading. A physical mixture of Pt, IrOx, and Nafion ionomer was inkjet printed directly on a Nafion membrane to fabricate varying loading bifunctional oxygen electrodes for a URFC and characterized via scanning electrode microscopy and cyclic voltammetry. The results show that the two catalyst do not interfere with one another and that an optimal electrode requires low ionomer loading, i.e., 10 wt%, and significantly lower amount of the IrOx catalyst compared to platinum, i.e., 3:1 Pt-IrOx ratio. A catalyst loading study shows that the highest round-trip efficiency is obtained at around 0.67 mgPt+IrOx/cm2 and further increasing the amount of catalyst does not result in a significant cell performance improvement either in water electrolysis or fuel cell mode. Overall, inkjet printing technique was used to fabricate thin bifunctional electrodes reaching round-trip efficiencies of up to 50% at 500 mA/cm2 using a bifunctional oxygen electrode with only 0.67 mgPt+IrOx/cm2 PGM catalyst loading, resulting in the highest efficiency by amount of catalyst reported to date.

Flexible transparent electrode with embedded silver mesh by eco-friendly polymer solution-assisted metal transfer process

Flexible transparent electrodes (FTEs) with an embedded metal meshes play an indispensable role in many high-performance optoelectronic devices due to their excellent mechanical stability and low-surface roughness. However, great challenges remain for achieving simple, cost-effective, and environmentally friendly manufacturing of FTEs with embedded metal mesh. In this work, a vacuum-free, mask-free, and plating-free fabrication technique is proposed for FTEs with embedded silver (Ag) mesh by combining an ink-jet printing technique and a newly developed eco-friendly polymer (polyvinyl alcohol) solution-assisted metal transfer process that does not use organic solvents. The fabricated FTEs exhibit excellent optoelectronic performance with an electrical resistance of ~ 1.6 Ω and an optical transmittance at 550 nm of ~ 85.98%. The FTEs with embedded Ag mesh show strong adhesion to the substrate due to their morphology features. The proposed technique offers a promising fabrication strategy with a cost-effective and environmentally friendly process for high-performance printed flexible electronics.Graphical abstract

InkJet-Printed Supercapacitor Electrodes of Graphene-Carboxymethyl Cellulose Biocomposite Ink

This work presents the preparation of mechanically exfoliated graphene-CMC biocomposite ink which was utilized in the printing process of SC individual electrodes via InkJet printing (IJP) technique. Three individual electrodes were fabricated using such technique with high abilities to control the geometry and tuning both resulting sheet resistance and thickness. The printer showed a good command of printing computer-aided designs with high resolution and fabricated well-homogenised patterns. The electrochemical behaviour of the fabricated electrodes was investigated in 0.1M NaOH. Results illustrate that electrodes have shown good capacitive behaviour and EDLC was the main energy storage mechanism. There was a direct relationship between the number of the printed layers and the resulting electrical parameters. A maximum areal capacitance of 16.58 mF/cm2 was achieved with printing 80 layers. Such results indicate that the formulated ink would be potential for electrochemical energy storage applications.

Aerosol Jet Printing-Enabled Dual-Function Electrochemical and Colorimetric Biosensor for SARS-CoV-2 Detection.

An aerosol jet printing-enabled dual-function biosensor for the sensitive detection of pathogens using SARS-CoV-2 RNA as an example has been developed. A CRISPR-Cas13:guide-RNA complex is activated in the presence of a target RNA, leading to the collateral trans-cleavage of ssRNA probes that contain a horseradish peroxidase (HRP) tag. This, in turn, catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by HRP, resulting in a color change and electrochemical signal change. The colorimetric and electrochemical sensing protocol does not require complicated target amplification and probe immobilization and exhibits a detection sensitivity in the femtomolar range. Additionally, our biosensor demonstrates a wide dynamic range of 5 orders of magnitude. This low-cost aerosol inkjet printing technique allows for an amplification-free and integrated dual-function biosensor platform, which operates at physiological temperature and is designed for simple, rapid, and accurate point-of-care (POC) diagnostics in either low-resource settings or hospitals.

Low-cost ceramic membranes manufacture using INKJET technology for active layer deposition and validation on membrane bioreactors

The fabrication of eco-friendly ceramic membranes based on low-cost raw materials, using digital INKJET printing techniques for active layer deposition and its validation in a membrane bioreactor (MBR) has been studied. The raw materials used in the manufacture of the support layer were UA50/2 clay, chamotte, calcium carbonate and potato starch. A MBR laboratory plant was operated to treat municipal wastewater with three ceramic membranes with different grammages in the selective layer deposition. The membrane performance at laboratory scale was evaluated in terms of transmembrane pressure (TMP) evolution for a constant permeate flux, permeate quality and mixed liquor characteristics. From these experiments, it was selected the membrane which obtained the lowest TMP profile maintaining appropriate water quality parameters (chemical oxygen demand (COD) removal percentage around 90% and turbidity around 0.06 NTU). This membrane was also operated at pilot plant scale in order to validate it at higher scale. Results indicated that TMP values were in the range of 0.06 and 0.1 bar, COD removal percentage was around 98% and microbiology analysis demonstrated that the quality of the effluent, according to European regulation 2020/741, can be classified as Class A and it can be reused for non-potable purposes.

Selective Growth of Graphene-Confined Inkjet-Printed Sn Nanoparticles on Plastic Using Intense Pulsed Light Annealing.

Printing graphene-based nanomaterials on flexible substrates has become a burgeoning platform for next-generation technologies. Combining graphene and nanoparticles to create hybrid nanomaterials has been proven to boost device performance, thanks to their complementary physical and chemical properties. However, high growth temperatures and long processing times are often required to produce high-quality graphene-based nanocomposites. For the first time, we report a novel scalable approach for additive manufacturing of Sn patterns on polymer foil and their selective conversion into nanocomposite films under atmospheric conditions. A combination of inkjet printing and intense flashlight irradiation techniques is studied. Light pulses that are selectively absorbed by the printed Sn patterns cause a temperature of over 1000 °C to be reached locally in a split second without damaging the underlying polymer foil. The top surface of the polymer foil at the interface with printed Sn becomes locally graphitized and acts as a carbon source, transforming printed Sn into Sn@graphene (Sn@G) core-shell patterns. Our results revealed a decrease in electrical sheet resistance, with an optimal value (Rs = 72 ± 2 Ω/sq) reached when light pulses with an energy density of 12.8 J/cm2 were applied. These graphene-protected Sn nanoparticle patterns exhibit excellent resistance against air oxidation for months. Finally, we demonstrate the implementation of Sn@G patterns as electrodes for Li-ion microbatteries (LIBs) and triboelectric nanogenerators (TENGs), showing remarkable performance. This work offers new insight into the development of a versatile, eco-friendly, and cost-effective technique for producing well-defined patterns of graphene-based nanomaterials directly on a flexible substrate using different light-absorbing nanoparticles and carbon sources.

Interaction of biopolymers with graphene for bio-electronic applications

Molecular modelling concepts always prove to be an efficient technique for studying the interaction between various substances prior to experimental work. They were utilized for investigating the interaction of chitosan (Cs) and carboxymethyl cellulose (CMC) biopolymers with a modified graphene structure (G). Geometry optimization calculations were carried out using PM6 method. Results illustrate that the proposed interactions are all stable; however, the interaction site has no role in the resulting energy values. The calculated energies for the G-CMC interactions are quite lower than those for the G-Cs ones indicating quite higher stability for the former group. On contrary to energy, the proposed interaction active site has a significant part in determining total dipole moment (TDM) and hence reactivity of the structures. The calculated quantitative structure-activity relationship (QSAR) parameters show that the interaction of graphene with these biopolymers lowers its hydrophobicity. Modification of Cs and CMC with graphene has a significant positive impact on enhancing their electrical features. The resulting bandgap of the proposed structures is lower than half of their original values. Bandgap values of the G-CMC proposed structures are quite lower than those of the G-Cs ones. An experimental trial was carried out by printing a sixty-layer simple electrode of both biocomposite inks via InkJet printing technique. Then, Sheet resistance and charge mobility measurements were conducted. Results demonstrate that the sheet resistance of the G-Cs printed electrode is about five times higher than that of the G-CMC one. Such result was confirmed by the measured Hall Effect measurement which showed that the charge mobility in the G-CMC electrode is much greater than that in the G-Cs one. Both theoretical and experimental parts agree that the G-CMC biocomposite has much more electrical conductivity than the G-Cs, proposing it as a potential candidate for bio-electronic applications.

Plasmon-enhanced photodetectors fabricated using digital inkjet-printing on chemically nanopatterned silicon wafers

In this study, we have fabricated and characterized three different configurations of photodetectors with digital inkjet printing techniques on different types of silicon substrates, such as pristine n-type silicon and chemically nanostructured n-type silicon, with and without Ag nanoparticle-induced surface-plasmon enhancement. Among these three comparison batches, digitally printed devices on chemically nanostructured n-type silicon with Ag nanoparticle-induced enhancement yield the highest photocurrent enhancement factor of 920×, the lowest rise and decay times of τr = 176 ms and τd = 98 ms, respectively, and the highest responsivity of 24.8 mA W−1 at wavelengths ranging from 380 to 700 nm. Most importantly, we demonstrate that these devices are highly stable after fabrication, losing less than 3% of their efficiency over 60 days under ambient conditions. We firmly believe that this simple device architecture and effective digital fabrication process are most promising for the realization of efficient, stable, and low-cost photodetectors fabricated at large scales.

Catalytic Modification of Porous Two-Dimensional Ni-MOFs on Portable Electrochemical Paper-Based Sensors for Glucose and Hydrogen Peroxide Detection.

Rapid and accurate detection of changes in glucose (Glu) and hydrogen peroxide (H2O2) concentrations is essential for the predictive diagnosis of diseases. Electrochemical biosensors exhibiting high sensitivity, reliable selectivity, and rapid response provide an advantageous and promising solution. A porous two-dimensional conductive metal-organic framework (cMOF), Ni-HHTP (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene), was prepared by using a one-pot method. Subsequently, it was employed to construct enzyme-free paper-based electrochemical sensors by applying mass-producing screen-printing and inkjet-printing techniques. These sensors effectively determined Glu and H2O2 concentrations, achieving low limits of detection of 1.30 μM and 2.13 μM, and high sensitivities of 5573.21 μA μM-1 cm-2 and 179.85 μA μM-1 cm-2, respectively. More importantly, the Ni-HHTP-based electrochemical sensors showed an ability to analyze real biological samples by successfully distinguishing human serum from artificial sweat samples. This work provides a new perspective for the use of cMOFs in the field of enzyme-free electrochemical sensing, highlighting their potential for future applications in the design and development of new multifunctional and high-performance flexible electronic sensors.

Printed Graphene Electrode for ITO/MoS2/Graphene Photodiode Application

Lightweight and flexible electronics have recently emerged at the forefront of optoelectronic applications. In this regard, graphene electrodes enable opportunities for new photodiode devices. In this paper, we formulated and tested graphene ink using the standard inkjet printing technique. It was shown that the maximum conductivity of ink was achieved for 14 print passes of the graphene layer. Moreover, we deposited Molybdenum Disulfide (MoS2) ink in the same pattern and used it as an active layer. We put MoS2 ink on an Indium-Tin-Oxide (ITO) glass substrate and then deposited graphene ink as a top electrode to fabricate an ITO/MoS2/graphene device. The fabricated device showed good rectification behavior and high ON/OFF switching behavior with a max photocurrent of 15 µA at +2 V. The technique thus paves the way for low-cost, low-temperature processing of electronics and one-step fabrication.

Preparation and Orthogonal Analysis for Dual-Responsive Electrochromic Polymer Dispersed Liquid Crystal Devices.

In this work, we provide a fabrication method for dual-responsive electrochromic (EC) polymer dispersed liquid crystal (PDLC) devices. The EC PDLC device was developed by combing the PDLC technique and a colored complex formed via a redox reaction without a specific EC molecule in a simple preparation method. The mesogen played dual roles in the device for scattering in the form of microdroplets and participating in the redox reactions. Orthogonal experiments were performed with the acrylate monomer concentration, the ionic salt concentration, and the cell thickness as factors to investigate the electro-optical performance for the achievement of optimized fabrication conditions. The optimized device presented four switchable states modulated by external electric fields. The light transmittance of the device was changed by an alternative current (AC) electric field while the color change was realized by a direct current (DC) electric field. Variations of mesogen and ionic salt species can modulate the color and hue of devices, which solves the disadvantage of a single color for traditional EC devices. This work lays the foundation for realizing patterned multi-colored patterned displays and anti-counterfeiting via screen printing and inkjet printing techniques.

Inkjet-Printed Ferrite Substrate-Based Vialess Waveguide Phase Shifter

Magnetically controlled waveguide-based phase shifters are desirable for their high performance, but are bulky and heavy, thus cannot be easily integrated with printed circuit board (PCB) based circuits. To tackle this, substrate-integrated waveguide (SIW) technology has been utilized, which brings the waveguide to a standard PCB, but requires large numbers of vias as well as multiple cavities in the substrate for ferrite slab placement. This implementation technique involves complex fabrication and yields a relatively low figure of merit (FoM). To alleviate this, we present the first completely vialess ferrite substrate-based waveguide phase shifter realized through low-cost inkjet printing technique. All the four sides of a yttrium iron garnet (YIG) substrate have been metalized through inkjet printing, allowing the fabrication of a conventional rectangular waveguide on a standard magnetic substrate. The prototype has been tested in symmetric as well as antisymmetric modes of biasing and peak FoMs of 160°/dB at 7.22 GHz and 332°/dB at 7.46 GHz have been measured, which are higher than those of the previously reported designs. This all-around inkjet printing approach can open the door to low-cost, integrable magnetic phase shifters with excellent RF performances.

High-throughput piezoelectric droplet dispenser driven by ultra-low voltage

Efficient and facile generation of tiny droplets is critical to many cutting-edge applications, such as flexible electronic skin, customized circuits, and micro-electro-mechanical systems. However, conventional piezoelectric inkjet printing techniques show more prominent problems of high driving voltage and relatively low printing frequency. Here, a novel principle for high-throughput droplet dispensing was proposed based on the resonance of the liquid column within the glass capillary. The mechanisms of this high-throughput piezoelectric droplet dispensing technique were studied both experimentally and theoretically. It is demonstrated experimentally that the resonance frequencies of different orders of the liquid column in the capillary fit perfectly with the theoretical value. It is further demonstrated that when the working frequency is close to the resonant frequency of piezoelectric ceramic, droplets can be ejected out by a driving voltage as low as 1 V. This ultra-low driving voltage and power consumption make this dispenser compatible with various digital transistor–transistor logic or complementary metal–oxide–semiconductor drive circuits without any power amplifier.

Solution-Route Inkjet Fabrication of CeO2 Thin Films with Tunable Microstructure.

We report the fabrication and characterization of solution-route CeO2 thin films with a tunable porosity and microstructure. Films were deposited by means of inkjet printing technique using 0.2 M, 0.4 M and 0.6 M concentration inks prepared from Ce(NO3)3·6H2O precursor. Printing was performed at two different temperatures of 60 °C and 300 °C to study the variation in structure. Printing parameters were adjusted for the consecutive deposition of layers, resulting in ≈140 nm and ≈185 nm thick single layers for 60 °C and 300 °C printing temperatures, respectively. We compared the microstructure of printed films for different concentrations, printing temperatures, solvents and substrates. The formation of the cubic fluorite structure of the printed films was confirmed via XRD characterization. We suggest this technique as an advanced method for high-quality film fabrication with a controlled microstructure and with a minimal waste of materials. Through adjusting printing parameters, both dense and porous films can be produced for use in different applications.

Drop-on-Demand Electrohydrodynamic Jet Printing of Microlens Array on Flexible Substrates

The inkjet-printing technique is regarded as an efficient method to fabricate microlens arrays used in digital cameras, medical endoscopes, displays, optical communication, and light source devices. The diameter, height, and aspect ratio of the microlens are the major contributors to these optical properties. Hence, the optical characteristics of the microlens array can vary with the type of inkjet-printing method. In this study, by employing electrohydrodynamic (EHD) jet printing with the drop-on-demand strategy, we fabricated microlenses and microlens arrays using a UV-curable photopolymer liquid on flexible poly(3,4-ethylenedioxythiophene):polystyrenesulfonate-coated poly(ethylene terephthalate). By controlling the number of printing drops, which is regarded as an efficient approach to control the dimension of the microlens, lenses with diameters of 11.9 ± 0.2 and 24.4 ± 0.5 μm and aspect ratio ranging from 0.22 to 0.33 were constructed. It was found that the focal length (15.44–26.79 μm), numerical aperture (0.39–0.46), and f-number (1.3–1.1) varied with the number of printing drops. The results demonstrate that the EHD-printed microlenses have a much shorter focal length, higher numerical aperture, and smaller f-number than the previously reported printed lenses. Hence, the EHD-printed microlens can be utilized to produce wide-angle-of-view applications and capture accurate images with insufficient light intensity. In addition, the proposed EHD-printing method may provide a cost-effective and simple route for manufacturing microlens arrays.