Temperature-Sensing Inks Using Electrohydrodynamic Inkjet Printing Technology

Paper-based microchannels are important components in paper-based microfluidic devices. Paper-based microchannels are usually manufactured by creating lines with hydrophobic patterns enclosing an area of hydrophilic paper inside. Among the many techniques for making hydrophobic lines, the printing method in general and inkjet printing in particular have become more common because of their advantages in terms of material saving, high precision, low-cost, etc. In this paper, the electrohydrodynamic (EHD) inkjet printing method, which has been studied and developed in recent years, has been used to drop glycol ether solvent-based ink onto a nitrocellulose paper. The results of the field emission scanning electron microscope (FE-SEM) show that the solvent based ink could dissolve through membrane and form a transparent hydrophobic layer on the created space. The width of the barrier lines can be controlled from about 200 μm to 260 μm, which is quite small when compared to other manufacturing methods. Based on this fabrication process, paper-based microfluidic analytical devices have been designed and fabricated for use in analytical biochemistry assays. Human chorionic gonadotropin (hCG) was selected as the biological target for this assay. Initial results have shown that the target for hCG can be quantitatively determined by these devices with a coefficient of determination (R2) of approximately 0.99. Therefore, EHD inkjet printing technology can be used for the manufacture of paper-based microfluidic analytical devices (μPADs) that may be applied in the future for analytical biochemistry assays.

Electrohydrodynamic (EHD) inkjet printing has gained widespread attention in electronics, biomedicine, and materials science for its exceptional resolution and printing versatility. However, the droplet formation process is governed by complex interactions between driving waveform parameters and fluid properties, making traditional trial-and-error optimization inefficient. To address this, a hybrid approach combining numerical simulation, machine learning regression, and genetic algorithm optimization is proposed to achieve precise control of droplet diameter. A multiphysics numerical model is established in COMSOL Multiphysics to simulate the complete cycle of Taylor cone formation, jetting, and droplet deposition under pulsed electric fields. Parametric studies are conducted to investigate the influence of waveform characteristics and fluid properties on droplet size and jetting stability. Based on these simulations, a dataset of 912 samples is constructed for machine learning analysis. Among seven regression models evaluated, the artificial neural network (ANN) shows the best predictive performance and is further integrated with a genetic algorithm to optimize the driving parameters for different target droplet diameters. Experimental validation is performed using a Super Inkjet (SIJ) printing system. The results confirm the effectiveness of the proposed method: the average droplet diameter error ranges from 1.00 μm to 1.89 μm, and 84.21% of the droplets fall within ±5% of the target diameter. This study demonstrates a practical and data-driven framework for enhancing precision and process control in EHD printing.

Electrohydrodynamic (EHD) inkjet printing has emerged as a powerful micro-/nanofabrication technique for high-resolution perovskite quantum dot (PeQD) color-conversion layers, offering precise control over pixel morphology, dimensions, and composition. This review systematically examines the mechanisms of cone-jet and electrostatic-attraction modes in EHD printing, highlighting recent advances in PeQD ink design, solvent and ligand engineering, and printing parameter optimization. Perovskite precursor and colloidal inks are discussed in detail, emphasizing strategies to enhance droplet ejection stability, suppress coffee-ring effects, and achieve uniform, high-luminescence pixels. Ligand exchange, dual-ligand passivation, and core−shell or polymer encapsulation are shown to effectively mitigate ion migration, surface defects, and environmental degradation, thereby improving photoluminescence efficiency and stability. Multi-channel and multi-nozzle EHD printing systems enable dynamic halide composition control and parallel RGB pixel deposition, facilitating ultrahigh-resolution patterning down to submicron feature sizes. Finally, the review highlights future directions, including synergistic PeQD material synthesis, advanced ink formulation, scalable high-throughput printing, and integration of PeQD color-conversion pixels into full-color micro-LED displays with minimal crosstalk and robust operational stability. These developments collectively demonstrate the immense potential of EHD inkjet printing for next-generation high-performance display technologies.

In this work we study the influence of dielectric surface and process parameters on the geometry and electrical properties of silver electrodes obtained by electrohydrodynamic inkjet printing. The cross-section and thickness of printed silver tracks are optimized to achieve a high conductivity. Silver overprints with cross-section larger than 4 μm2 and thickness larger than 90 nm exhibit the lowest resistivity. To fabricate electrodes in the desired geometry, a sufficient volume of ink is distributed on the surface by applying appropriate voltage amplitude. Single and multilayer overprints are incorporated as bottom contacts in bottom gate organic field-effect transistors (OFETs) with a semiconducting polymer as active layer. The multilayer electrodes result in significantly higher electrical parameters than single layer contacts, confirming the importance of a careful design of the printed tracks for reliable device performance. The results provide important design guidelines for precise fabrication of electrodes in electronic devices by electrohydrodynamic inkjet printing.

Design, Development and Experimental Investigation of E-jet Based Additive Manufacturing Process

Electrodes, as signal transmission channels for microelectronic components, need to develop towards high precision. Among the existing printed electronic technologies, electrohydrodynamic (EHD) jet printing utilizes electric field force to control ink, enabling higher precision electrode processing. In this paper, the relationship between the printing parameters of EHD-printer and the morphology of the electrodes was investigated. With the decreasing of driving voltage and bias voltage, the line width of the silver electrode became more and more narrow. Silver electrodes with line width of 3.85 µm were fabricated through process optimization. In addition, with the annealing temperature rising, the resistivity of the electrode gradually decreased. The possible reason was that higher temperatures could not only increase the binding degree of silver nanoparticles, but also promote the removal of organic matter. Silver electrodes with resistivity of 13.63 µΩ cm were fabricated through process optimization, which showed an important application potential of the silver electrode printed by electrohydrodynamic inkjet printing.

As demands for high pixel densities and wearable forms of displays increase, high-resolution printing technologies to achieve high performance transistors beyond current amorphous silicon levels and to allow low-temperature solution processability for plastic substrates have been explored as key processes in emerging flexible electronics. This study describes electrohydrodynamic inkjet (e-jet) technology for direct printing of oxide semiconductor thin film transistors (TFTs) with high resolution (minimum line width: 2 μm) and superb performance, including high mobility (∼230 cm2 V-1 s-1). Logic operations of the amplifier circuits composed of these e-jet-printed metal oxide semiconductor (MOS) TFTs demonstrate their high performance. Printed In2O TFTs with e-jet printing-assisted high-resolution S/D electrodes were prepared, and the direct printing of passivation layers on these channels enhanced their gate-bias stabilities significantly. Moreover, low process temperatures (<250 °C) enable the use of thin plastic substrates; highly flexible and stretchable TFT arrays have been demonstrated, suggesting promise for next-generation printed electronics.

Electrohydrodynamic (EHD) printing is an additive manufacturing technique capable of microscale and nanoscale structures for biomedical, aerospace, and electronic applications. To realize stable printing at its full resolution, the monitoring of jetting behavior while printing and optimization of the printing process are necessary. Various machine vision control schemes have been developed for EHD printing. However, in-line machine vision systems are currently limited because only limited information can be captured in situ toward quality assurance and process optimization. In this article, we presented a machine learning-embedded machine vision control scheme that is able to characterize jetting and recognize the printing quality by using only low-resolution observations of the Taylor Cone. An innovative approach was introduced to identify and measure cone-jet behavior using low-fidelity image data at various applied voltage levels, stand-off distances, and printing speeds. The scaling law between voltages and the line widths enables quality prediction of final printed patterns. A voting ensemble composed of k-nearest neighbor (KNN), classification and regression tree (CART), random forest, logistic regression, gradient boost classifier, and bagging models was employed with optimized hyperparameters to classify the jets to their corresponding applied voltages, achieving an 88.43% accuracy on new experimental data. These findings demonstrate that it is possible to analyze jetting status and predict high-resolution pattern dimensions by using low-fidelity data. The voltage analysis based on the in situ data will provide additional insights for system stability, and it can be used to establish the error functions for future advanced control schemes.

Parametric Optimization of E-Jet Based Micro Manufacturing System through Hybrid Taguchi Methodology

Microlens arrays (MLAs) are essential for light collection, extraction, and high-resolution imaging. However, most reported MLAs have a limited filling factor. Here, we demonstrate MLAs using three different UV-curing optical adhesives based on the electrohydrodynamic inkjet (E-jet) printing technique. The highest filling factor of 89.91% is achieved. By controlling the curvature of the microlens via the surface treatment of the substrate, a series of MLAs with different numerical apertures can be obtained. With the high-consistency printing technique, the demonstrated high filling factor MLAs could be potentially useful to improve the performance of optical imaging and sensing systems.

High-resolution electrohydrodynamic (EHD) printing of radio frequency identification (RFID) antenna are highly desirable. Also, some traditional post-processing treatment methods have many limitations. Herein, high-resolution EHD printing and joining of AgNWs were combined to fabricate RFID antennas with a high resolution of 50 μm by introducing silver ions in the AgNW ink. During the process of silver ions-assisted nanosoldering EHD printing, the Ag ions are reduced when the droplet produced by EHD printing reaches the substrate and then selectively deposit near the junctions of AgNWs, thus improving the sheet resistance from 20.8 Ω•sq <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> to 15.6 Ω•sq <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . Based on this new method and its high resolution, flexible RFID antennas were fabricated. The RF performance, bending reliability, folding reliability, and low-temperature reliability of silver-assisted antenna is more superior than pure AgNW antenna.

Electrohydrodynamic (EHD) printing is a promising micro-nano manufacturing technology. However, the EHD printing process is susceptible to interferences like charge repulsion, electric field, airflow, and platform motion, leading to unstable jetting and nonuniform deposition morphology. In this paper, a double close-loop fuzzy control method based on jet image recognition and micro-current measurement was designed to monitor and control the EHD printing process. A closed-loop control based on the fuzzy control algorithm has been designed to monitor the EHD printing system by taking the feedback information from micro-current and jet image. The experimental results show that the closed-loop control significantly improved the uniformity and stability of the fiber deposition. The volatility percentage of the current decreased from 34% to 12%, the fluctuation range of the fiber diameter was reduced from 35μm to 15μm, and the volatility percentage of the fiber spacing decreased from 29% to 9.5%. Additionally, the closed-loop control accelerated the response speed of jet mode conversion. Ineffective deposition of printing jet on the collection plate was shortened from 5s to 2.2s. This feedback control optimises the printing quality of micro-nano structures, promoting the advancement of high-resolution additive manufacturing applications.

Study effects of particle size in metal nanoink for electrohydrodynamic inkjet printing through analysis of droplet impact behaviors

Electrohydrodynamic (EHD) printing is a micro–nano printing technology based on the principles of electric field and fluid dynamics. It is characterized by high resolution, high precision, and high speed, applied to various materials, including metals, ceramics, and organic materials. Compared with traditional printing technologies, EHD printing offers advantages such as low manufacturing cost, simple process, and direct fabrication, making it highly promising in the field of micro–nano manufacturing. Polyethylene oxide (PEO) is a highly water‐soluble polymer that has been widely used in various fields due to its low toxicity and ease of processing. In this study, a finite element simulation model was developed using simulation software to simulate and analyze the mechanisms of focused jetting and deposition of PEO solution under an electric field. Based on the principles of electrohydrodynamics, a self‐built EHD printing system was used to investigate the influence of different solution mass fractions and printing parameters on fiber formation, and the optimal process window of EHD printing PEO solution was obtained. Ultimately, ordered deposition of fiber lines ranging from 1.761 to 6.093 μm was achieved. The simulation results were consistent with the experimental results, validating the effectiveness of the established model in guiding jetting outcomes.Highlights Independently building a low‐cost electrohydrodynamic (EHD) printing system. Finite element simulation of EHD printing process. Mechanism analysis of PEO solution jetting and deposition. Optimal process window for PEO solution EHD printing. Influence of key process parameters on fiber forming width.

Electrohydrodynamic (EHD) printing, which adopts electrical force to pull the jet from nozzle, is a hotspot of printing techniques, due to its unique advantages of high-resolution (50 nm) and compatibility with wide range of inks (1–10,000 cps). EHD printing is rooted in the traditional electrospinning, which is an effective method for micro/nano fibers generation, but has difficulties in orientation and controllability. Recently, considerable improvements have been made to realize electrohydrodynamic direct writing for micro/nano manufacturing, e.g. MES and HE-Printing techniques to enhance the controllability on the positioning and morphology of fibers, various functional inks adopted to widespread its applications, design and fabrication of nozzles to improve printing efficiency and accuracy, and control methods of EHD printing to achieve online modulating. High precision EHD printing equipment that integrates the latest technology is the core to realize practical micro/nano manufacturing, however, most of the apparatuses are in the laboratory level with limited functionality and accuracy. This chapter first summarizes the necessary features of EHD equipment with a multifunction of three printing modes (drop on demand, electrospinning and electrospray) for various viscosity inks in Sect. 7.1. Basic comprising modules of the EHD printer are also introduced in this section, as well as its extension modules including printing environment control, roll to roll, and nozzle array. Then some specific applications of stretchable generator, gas sensor and flexible small-channel thin-film transistors that generated based on high resolution EHD printing equipment are demonstrated in Sects. 7.2, 7.3 and 7.4 respectively.