Electrohydrodynamic Jet Printing Research Articles

Stepwise Aggregation Control of PEDOT:PSS Enabled High-Conductivity, High-Resolution Printing of Polymer Electrodes for Transparent Organic Phototransistors.

Electrohydrodynamic (EHD) jet printing is a widely employed technology to create high-resolution patterns and thus has enormous potential for circuit production. However, achieving both high conductivity and high resolution in printed polymer electrodes is a challenging task. Here, by modulating the aggregation state of the conducting polymer in the solution and solid phases, a stable and continuous jetting of PEDOT:PSS is realized, and high-conductivity electrode arrays are prepared. The line width reaches less than 5 μm with a record-high conductivity of 1250 S/cm. Organic field-effect transistors (OFETs) are further developed by combining printed source/drain electrodes with ultrathin organic semiconductor crystals. These OFETs show great light sensitivity, with a specific detectivity (D*) value of 2.86 × 1014 Jones. In addition, a proof-of-concept fully transparent phototransistor is demonstrated, which opens up new pathways to multidimensional optical imaging.

PZT thick film element balancing flexibility with piezoelectricity fabricated by electrohydrodynamics jet printing used for micro power generator

In this paper, a novel flexible piezoelectric thick-film generator is proposed to address the challenges caused by flexible deformation and high piezoelectricity. This improves the output charge of the generator, which breaks the limitation imposed by the rigid and brittle nature of traditional piezoelectric bulks on elastic strain and piezoelectric performance. Additionally, the low piezoelectric coefficient of piezoelectric polymer-based piezoelectric generators is also resolved. Given the high thickness precision of electrohydrodynamic jet printing technology, the facile production of 10-μm thick film components is achieved through a process of printing and layer-by-layer accumulation on a flexible substrate, which ensures the flexible deformation and piezoelectric characteristics of the functional film. To ensure that AC is converted into stable DC output, a bipolar charge collection circuit is developed. The printed thick film produces an excellent performance in surface uniformity and smoothness. Notably, the piezoelectric constant d33 is measured to be approximately 80 pC/N, which is five times higher than the d33 value of flexible PVDF films. Additionally, the strength of adhesion between the printed thick film and the flexible substrate is remarkably high, reaching up to 20 N, which is an order of magnitude higher than the magnetron sputtering method. In a single cycle, the forward charge output reaches an impressively high level of 260 nC, which is approximately thirteen times the charge transfer capability of PVDF flexible generator. Furthermore, a bipolar charge collection circuit is applied to convert AC into DC effectively. This increases the output voltage from 2 V to 4 V. The illumination of commercial electronic screens and 39 LED lights demonstrates the applicability of micron-scale jet-printed thick films in micro-energy harvesting.

Fabrication of SU-8 polymer micro/nanoscale nozzle by hot embossing method

Electrohydrodynamic-jet printing (E-jet printing) is a direct-writing technology for manufacturing micro-nano devices. To further reduce the inner diameter of the nozzle to improve the printing resolution, a large-scale manufacturing method of SU-8 polymer micro/nanoscale nozzle by means of a process combining UV exposure and hot embossing was proposed. To improve the adhesive strength between the UV mask and SU-8, the influence of the oxygen plasma treatment parameters on the water contact angles of the UV mask was analyzed. The effect of hot embossing time and temperature on the replication precision was studied. The influence of UV exposure parameters and thermal bonding parameters on the micro and nanochannel pattern was investigated. The SU-8 polymer nozzles with 188 ± 3 nm wide and 104 ± 2 nm deep nanochannels were successfully fabricated, and the replication precision can reach to 98.5%. The proposed manufacturing method of SU-8 polymer nozzles in this study will significantly advance the research on the transport properties of nanoscale channels in E-jet nozzles and facilitate further advancements in E-jet based applications.

Preparation of high-resolution micro/nano dot array by electrohydrodynamic jet printing with enhanced uniformity

The high-resolution array is the basic structure of most kinds of microelectronics. Electrohydrodynamic jet (E-Jet) printing technology is widely applied in manufacturing array structures with high resolution, high material compatibility and multi-modal printing. It is still challenging to acquire high uniformity of printed array with micro-nanometer resolution, which greatly influences the performance and lifetime of the microelectronics. In this paper, to improve the uniformity of the printed array, the influence of each parameter on the uniformity of the E-jet printed dot array is studied on the cobuilt NEJ-E/P200 experimental platform, finding the applied voltage plays the most important role in maintaining the uniformity of the printed array. By appropriately adjusting the printing parameters, the dot arrays with different resolutions from 500 pixels per inch (PPI) to 17,000 PPI are successfully printed. For arrays below and over 10,000 PPI, the deviations of the uniformity are within 5% and 10% respectively. In this work, the dot array over 15,000 PPI is first implemented using E-jet printing. The conclusions acquired by experimental analysis of dot array printing process are of great importance in high resolution array printing as it provides practical guidance for parameters adjustment.

In situ preparation of SnO2/Pd@TiO2 bilayer sensor for highly sensitive and fast detection of H2S based on electrohydrodynamic jet printing

A micron-scale bilayer H2S sensor fabricated by electrohydrodynamic (EHD) jet printing in situ was evaluated. The prepared sensor consisted of a Pd@TiO2 cover layer (porous catalytic sensing layer), a SnO2 bottom layer (electron transport layer) and a Sn-Ti transition layer between them. The addition of TiO2 nanoparticles to the cover layer led to a porous structure after one-step sintering. The increase in specific surface area and the formation of heterojunction effectively improved the sensor sensitivity. The PdO nanoparticles loaded on the surface of TiO2 nanoparticles further improved the performance due to its catalysis. Since the kinetic energy of droplets of the same size generated by EHD inkjet printing is about 48 times that of inkjet printing, the film density is much higher than that of inkjet printing. The relatively dense bottom layer, and the thick and stable transition layer improved the long-term stability of the sensor. The detection limit of the sensor is 6 ppb, with linear range of 0.02–10 ppm H2S. The response and recovery times are 7 s and 45 s (2 ppm H2S), respectively. After 9 months of intermittent measurement, the response of the sensor to 2 ppm H2S decreased by only 10.6%.

Flexible Patterned Electrohydrodynamic Jet Printing Using Orthogonal Deflection Electrodes.

Electrohydrodynamic jet (E-Jet) printing technology provides unmatched advantages in the fabrication of patterned micro/nanostructures. However, the rapid jets generated during printing can lead to localized droplet accumulation on complex structures due to the relatively slow motion control achieved with motorized translation stages, resulting in distorted patterns. To address this challenge, we introduce two jet-deflecting electrodes orthogonally placed on each other, which can rapidly change the electric field in the vicinity of the jet and thus flexibly adjust the flight trajectory of the fast jet to avoid the region where droplets have been deposited. In this way, the jet droplets are precisely controlled to generate high-fidelity microstructures with arbitrary predefined patterns on the stationary substrate. The maximum deflection distance of the jet droplets reaches several hundred microns. Furthermore, the positioning error of the printed structure is less than 3%. Moreover, we successfully obtained a diverse range of complex patterns by combining this technique with stage motion. This innovative printing technology not only enables the fabrication of complex patterned structures with high fidelity but also opens up exciting possibilities for new applications that require complete control of fast droplet positioning.

PH Tunable Patterning of Quantum Dots.

Patterning of quantum dots (QDs) is essential for many, especially high-tech, applications. Here, pH tunable assembly of QDs over functional patterns prepared by electrohydrodynamic jet printing of poly(2-vinylpyridine) is presented. The selective adsorption of QDs from water dispersions is mediated by the electrostatic interaction between the ligand composed of 3-mercaptopropionic acid and patterned poly(2-vinylpyridine). The pH of the dispersion provides tunability at two levels. First, the adsorption density of QDs and fluorescence from the patterns can be modulated for pH > ≈4. Second, patterned features show unique type of disintegration resulting in randomly positioned features within areas defined by the printing for pH ≤ ≈4. The first capability is useful for deterministic patterning of QDs, whereas the second one enables hierarchically structured encoding of information by generating stochastic features of QDs within areas defined by the printing. This second capability is exploited for generating addressable security labels based on unclonable features. Through image analysis and feature matching algorithms, it is demonstrated that such patterns are unclonable in nature and provide a suitable platform for anti-counterfeiting applications. Collectively, the presented approach not only enables effective patterning of QDs, but also establishes key guidelines for addressable assembly of colloidal nanomaterials.

Electrohydrodynamic jet printed bioinspired piezoelectric hair-like sensor for high-sensitivity air-flow detection

Inspired by the highly sensitive hairs of creatures in nature, this work proposes a high-aspect-ratio piezoelectric sensor that is processed using electrohydrodynamic jet (E-jet) printing technology. A thin layer of piezoelectric material is directly written on the surface of tungsten steel microwire by E-jet printing. The piezoelectric material was crystallized by high-temperature annealing and fully bonded to the microwire. The annealed piezoelectric thin film was then sputtered with copper electrodes which forms a piezoelectric hair-like sensor with a diameter of 120 μm and an aspect ratio of 300. It was observed that the piezoelectric hair-like sensor generates 18 mV with a displacement of 100 μm. The output signal increases linearly with the increase of lateral displacement and velocity. It was examined that the piezoelectric hair-like sensor can detect airflow velocity as low as 0.01 m s−1, which shows a lower detection threshold compared to piezoelectric hair-like airflow sensors processed in other ways. In addition, the piezoelectric hair-like sensor allows for the detection of an airflow velocity of 10 m s−1 and a response time of 70 ms. The experimental results show that the piezoelectric hair-like sensor has high sensitivity, a wide detection range and rapid detection response, which is expected to be a high-performance sensor for biosensing and airflow monitoring.

Improving the Electrical Properties of Zinc-Tin Oxide Thin-Film Transistors by Additive using Electrohydrodynamic Jet Technology

Oxide thin-film transistors (TFTs) are important semiconductor materials for display backplanes. To fabricate flexible displays, not only display modes but also TFTs are important. Flexible TFTs are especially needed for flexible displays, and related processes need to be developed. Printing is a good choice for the new fabrication of oxide TFTs. Electrohydrodynamic (EHD) jet printing is an excellent alternative for making flexible TFTs. To improve the electrical properties of oxide TFTs using EHD jet printing, propylene monomethyl ether acetate (PGMEA) was added to a zinc-tin oxide (ZTO) formulation. EHD jet printing was performed by Taylor cone jet mode with parameters of 2.4 kV and 0.064 µL/s to obtain uniform thin films at a substrate temperature of 50oC. Much improved TFT properties were obtained, including a mobility of 7.11 cm2/V s, on-to-off current ratio of 2.8 × 106 and subthreshold slope of 1.44 V/dec for ZTO TFT with 5 wt% of PGMEA, and a mobility of 1.43 cm2/V s, on-to-off current ratio of 2.7 × 105 and subthreshold slope of 1.32 V/dec for the ZTO TFT. Almost no hysteresis behavior was observed in the oxide TFTs with added PGMEA. We report a new way to improve the electrical properties of oxide TFTs, by the simple addition of PGMEA.

Polymer nano nozzle fabricated by nanoscale electrohydrodynamic jet printing for high-resolution printing of low-viscosity inks

Electrohydrodynamic jet (E-jet) printing has emerged as a promising manufacturing technique in many areas due to its high efficiency, low cost, high resolution, and wide adaptability of materials. However, achieving further advancements in print resolution to the submicron and even nanoscale, particularly for low-viscosity inks with significant spread, requires nozzles with diameters in the hundreds of nanometers. It is particularly challenging and complicated to manufacture nozzles with such small diameters. In this paper, a concise method based on high-resolution E-jet printing was developed to fabricate nano-nozzles, which in turn enable high-resolution printing of a range of low-viscosity inks. First, the hybrid polymer nozzle mold consisting of BN303 nanomesa and SU-8 micromesa was fabricated by E-jet printing and ultraviolet (UV) lithography. Subsequently, the polymer nozzle was produced through a casting process of polydimethylsiloxane (PDMS) and subsequent bonding. In addition, the preliminary E-jet printing was performed with poly (3-hexylthiophene) (P3HT) ink using the polymer nozzle, resulting in lines as small as 140 nm. These outcomes demonstrate the compatibility of E-jet printing with high resolution and showcase the potential of the developed polymer nano-nozzles to significantly expand the scope of E-jet printing applications.

Robust Higher-Order Spatial Iterative Learning Control for Additive Manufacturing Systems

In this article, a higher-order spatial iterative learning control (HO-SILC) scheme is proposed, targeting heightmap tracking for a class of 3-D structures fabricated by repetitive addition of material in a layer-by-layer fashion using additive manufacturing (AM) technology. AM processes are innately iteration-varying, resulting in large model uncertainties due to iteration-varying system parameters and surface variations. HO-SILC has been shown to be useful in repetitive systems with model uncertainties by improving system performance with respect to convergence speed and robustness. In this article, HO-SILC is used to iteratively construct a feedforward control signal to improve part quality in multilayered AM constructs. The system dynamics are approximated by discrete 2-D spatial convolution kernels that incorporate in-layer and layer-to-layer variations. The proposed HO-SILC framework incorporates data available from previously printed devices, as well as multiple previously printed layers, to enhance the overall performance. The condition for robust monotonic convergence (RMC) of the iteration-varying HO-SILC algorithm is based on the Lyapunov stability criteria. Simulation results of an AM process termed electrohydrodynamic jet (e-jet) printing demonstrate that a well-designed HO-SILC framework is effective and can improve the performance by 60 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\%$</tex-math> </inline-formula> . In addition, HO-SILC is robust to iteration-varying model uncertainties, especially at higher layers where iteration-varying surface variations are more pronounced.

Flexible conductive patterns using electrohydrodynamic jet printing method based on high-voltage electrostatic focusing lens

Flexible conductive patterns using electrohydrodynamic jet printing method based on high-voltage electrostatic focusing lens

Recent Progress in Electrohydrodynamic Jet Printing for Printed Electronics: From 0D to 3D Materials

Advanced micro/nano-flexible sensors, displays, electronic skins, and other related devices provide considerable benefits compared to traditional technologies, aiding in the compactness of devices, enhancing energy efficiency, and improving system reliability. The creation of cost-effective, scalable, and high-resolution fabrication techniques for micro/nanostructures built from optoelectronic materials is crucial for downsizing to enhance overall efficiency and boost integration density. The electrohydrodynamic jet (EHD) printing technology is a novel additive manufacturing process that harnesses the power of electricity to create fluid motion, offering unparalleled benefits and a diverse spectrum of potential uses for microelectronic printing in terms of materials, precision, accuracy, and cost-effectiveness. This article summarizes various applications of EHD printing by categorizing them as zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) printing materials. Zero-dimensional (quantum dot) materials are predominantly utilized in LED applications owing to their superb optoelectronic properties, high color fidelity, adjustable color output, and impressive fluorescence quantum yield. One- and two-dimensional materials are primarily employed in FET and sensor technologies due to their distinctive physical structure and exceptional optoelectronic properties. Three-dimensional materials encompass nanometals, nanopolymers, nanoglass, and nanoporous materials, with nanometals and nanopolymers finding widespread application in EHD printing technology. We hope our work will facilitate the development of small-feature-size, large-scale flexible electronic devices via EHD printing.

High-performance flexible organic field effect transistors with print-based nanowires

Polymer nanowire (NW) organic field-effect transistors (OFETs) integrated on highly aligned large-area flexible substrates are candidate structures for the development of high-performance flexible electronics. This work presents a universal technique, coaxial focused electrohydrodynamic jet (CFEJ) printing technology, to fabricate highly aligned 90-nm-diameter polymer arrays. This method allows for the preparation of uniformly shaped and precisely positioned nanowires directly on flexible substrates without transfer, thus ensuring their electrical properties. Using indacenodithiophene-co-benzothiadiazole (IDT-BT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8-BT) as example materials, 5 cm2 arrays were prepared with only minute size variations, which is extremely difficult to do using previously reported methods. According to 2D-GIXRD analysis, the molecules inside the nanowires mainly adopted face-on π-stacking crystallite arrangements. This is quite different from the mixed arrangement of thin films. Nanowire-based OFETs exhibited a high average hole mobility of 1.1 cm2 V−1 s−1 and good device uniformity, indicating the applicability of CFEJ printing as a potential batch manufacturing and integration process for high-performance, scalable polymer nanowire-based OFET circuits. This technique can be used to fabricate various polymer arrays, enabling the use of organic polymer semiconductors in large-area, high-performance electronic devices and providing a new path for the fabrication of flexible displays and wearable electronics in the future.

Physics-Informed Bayesian learning of electrohydrodynamic polymer jet printing dynamics

Calibration of highly dynamic multi-physics manufacturing processes such as electrohydrodynamics-based additive manufacturing (AM) technologies (E-jet printing) is still performed by labor-intensive trial-and-error practices. Such practices have hindered the broad adoption of these technologies, demanding a new paradigm of self-calibrating E-jet printing machines. Here we develop an end-to-end physics-informed Bayesian learning framework (GPJet) which can learn the jet process dynamics with minimum experimental cost. GPJet consists of three modules: the machine vision module, the physics-based modeling module, and the machine learning (ML) module. GPJet was tested on a virtual E-jet printing machine with in-process jet monitoring capabilities. Our results show that the Machine Vision module can extract high-fidelity jet features in real-time from video data using an automated parallelized computer vision workflow. The Machine Vision module, combined with the Physics-based modeling module, can also act as closed-loop sensory feedback to the Machine Learning module of high- and low-fidelity data. This work extends the application of intelligent AM machines to more complex working conditions while reducing cost and increasing computational efficiency.

Nib-Assisted Coaxial Electrohydrodynamic Jet Printing for Nanowires Deposition.

This paper presents the concrete design of nanowires under the precise size and morphology that play a crucial role in the practical operation of the micro/nano devices. A straightforward and operative method termed as nib-assistance coaxial electrohydrodynamic (CEHD) printing technology was proposed. It extracts the essence of a nib-assistance electric field intensity to enhance and lessen the internal fluid reflux of the CEHD jet. The experiments were performed to add microparticles into the inner liquid to indicate the liquid flow consistency within the coaxial jet. The reflux in the coaxial jet was observed for the first time in experiments. The nanowires with a minimum size of 70 nm were printed under optimum experimental conditions. The nanopatterns contained aligned nanowires structures with diameters much smaller than the inner diameter of nozzle, relying on the coaxial nib-assisted technique. The printed results revealed that the nib-assisted CEHD printing technique offers a certain level high quality for application of NEMS system.

PZT Composite Film Preparation and Characterization Using a Method of Sol-Gel and Electrohydrodynamic Jet Printing.

Lead zircon titanate (PZT) composite films were advantageously prepared by a novel hybrid method of sol-gel and electrohydrodynamic jet (E-jet) printing. PZT thin films with thicknesses of 362 nm, 725 nm and 1092 nm were prepared on Ti/Pt bottom electrode via Sol-gel method, and then the PZT thick films were printed on the base of the PZT thin films via E-jet printing to form PZT composite films. The physical structure and electrical properties of the PZT composite films were characterized. The experimental results showed that, compared with PZT thick films prepared via single E-jet printing method, PZT composite films had fewer micro-pore defects. Moreover, the better bonding with upper and lower electrodes and higher preferred orientation of crystals were examined. The piezoelectric properties, dielectric properties and leakage currents of the PZT composite films were obviously improved. The maximum piezoelectric constant of the PZT composite film with a thickness of 725 nm was 69.4 pC/N, the maximum relative dielectric constant was 827 and the leakage current was reduced to 1.5 × 10-6A at a test voltage of 200V. This hybrid method can be widely useful to print PZT composite films for the application of micro-nano devices.

Physics of moderately stretched electrified jets in electrohydrodynamic jet printing.

Electrohydrodynamic (EHD) jet printing involves the deposition of a liquid jet issuing from a needle stretched under the effect of a strong electric field between the needle and a collector plate. Unlike the geometrically independent classical cone-jet observed at low flow rates and high applied electric fields, at a relatively high flow rate and moderate electric field, EHD jets are moderately stretched. Jetting characteristics of such moderately stretched EHD jets differ from the typical cone-jet due to the nonlocalized cone-to-jet transition. Hence, we describe the physics of the moderately stretched EHD jet applicable to the EHD jet printing process through numerical solutions of a quasi-one-dimensional model of the EHD jet and experiments. Through comparison with experimental measurements, we show that our simulations correctly predict the jet shape for varying flow rates and applied potential difference. We present the physical mechanism of inertia-dominated slender EHD jets based on the dominant driving and resisting forces and relevant dimensionless numbers. We show that the slender EHD jet stretches and accelerates primarily due to the balance of driving tangential electric shear and resisting inertia forces in the developed jet region, whereas in the vicinity of the needle, driving charge repulsion and resisting surface tension forces govern the cone shape. The findings of this study can help in operational understanding and better control of the EHD jet printing process.

Computational Study of Drop-on-Demand Coaxial Electrohydrodynamic Jet and Printing Microdroplets

Currently, coaxial electrohydrodynamic jet (CE-Jet) printing is used as a promising technique for the alternative fabrication of drop-on-demand micro- and nanoscale structures without using a template. Therefore, this paper presents numerical simulation of the DoD CE-Jet process based on a phase field model. Titanium lead zirconate (PZT) and silicone oil were used to verify the numerical simulation and the experiments. The optimized working parameters (i.e., inner liquid flow velocity 150 m/s, pulse voltage 8.0 kV, external fluid velocity 250 m/s, print height 16 cm) were used to control the stability of the CE-Jet, avoiding the bulging effect during experimental study. Consequently, different sized microdroplets with a minimum diameter of ~5.5 µm were directly printed after the removal of the outer solution. The model is considered the easiest to implement and is powerful for the application of flexible printed electronics in advanced manufacturing technology.

Substrate‐Independent Electrohydrodynamic Jet Printing with Dual‐Ring Electrostatic Focusing Structure

AbstractElectrohydrodynamic jet (E‐Jet) printing is one of the most effective methods for fabricating micro/nanostructures due to its high‐resolution, broad material adaptability, and simple process. However, printing high‐resolution patterns on curved or insulated substrates still is of a great challenge because it is quite difficult to keep the electric field distribution stable between the nozzle and the substrate during the printing process. To address these issues, a dual‐ring electrostatic focused electrohydrodynamic jet (DEFEJ) printing method is proposed. In this technique, a microtip with a radius of curvature (ROC) of several micrometers is placed in a conductive dual‐ring structure to form the built‐in electrostatic focusing and drive the Taylor cone. The high‐speed jets then fall on the substrate due to their own motion inertia, eliminating the influence of the substrate curvature and its conductivity on the electric field distribution. Submicrometer droplets with an average diameter of about 0.83 µm are obtained using a 10‐µm‐ROC microtip. In addition, high‐resolution microstructure patterns are also printed on substrates with different conductivity and curvature. This DEFEJ printing method not only has the same printing accuracy as conventional E‐Jet printing, but also can significantly increase the adaptability of E‐Jet printing to different substrates.