Drop-on-demand Inkjet Printing Research Articles

Understanding Key Factors during Dod Inkjet Printing Towards Precise Fabrication of Micro Energy Systems

There is an ever-increasing need for micro energy systems that can power miniature, unmanned, or remotely-located devices. Drop-on-Demand (DOD) inkjet fabrication is uniquely positioned for this demand due to its low-cost processing with microscale resolution, high throughput, reproducibility, and ease in shape design. This study seeks to capitalize on the advantages of DOD inkjet printing for application to manufacturing micro energy conversion/storage systems, by defining the fundamental jet kinematics and key factors underpinning the inkjet printing process.The ink used in this study was a dilute colloidal ink suspension composed of a common solid oxide fuel cell (SOFC) cathode material [La0.6Sr0.4Fe0.8Co0.2O3 (LSFC)] and organic solvent α-terpineol. The results were evaluated systematically in terms os final deposition quality, resolution, and microstructure. Favorable fluid kinematics were identified that attained uniform, well-shaped, circular 0-D dots about 0.1 µm thick and 60 µm in diameter. To increases the microfeature thickness and x/y plane dimensions , multiple and/or sequential ink passes were employed. For printing 1-D lines, the spacing between droplets was imperative to fabricating quality micro features. Using appropriate conditions, 1-D lines with x/y dimensions < 100 µm and controllable z axis dimensions at 0.1 µm per printing pass with dense, open or networked microstructures were demonstrated. 2-D planes at the dimensions as small as 100 µm by 100 µm were also achieved with smooth surface and continuous intra-planar ceramic coverage. In the course of post-processing the inkjetted cathodes, it was observed that the submicron cathode films printed at optimal conditions, after being sintered at controlled conditions, were uniform, smooth and free of cracks or delamination.This research demonstrated through fundamental understanding and control of the inkjet fabrication process, cathode features can be printed with controlled dimension and quality towards producing a functioning micro SOFC operable at low temperatures. The knowledge gained from this research will be appliable to other micro energy conversion and storage systems.

Drop-on-demand (DOD) inkjet dynamics of printing viscoelastic conductive ink

Emerging applications of drop-on-demand (DOD) inkjet printing, such as printed electronics and bioprinting, are leading to an ever-increasing development of diverse functional inks with complex chemical and rheological properties, especially viscoelastic polymers. Forming droplets with desirable velocity and volume as well as excellent reliability is of great importance for successful printing. In this study, the dynamics and performance of droplet formation during DOD inkjet printing of viscoelastic ink were investigated by employing the piezoelectric inkjet technology to print a conductive polymer ink under various excitation waveform parameters. Four distinct droplet formation regimes were identified, namely, no droplet formation, a single droplet, one satellite droplet, and multiple satellite droplets. A process dynamics-related dimensionless number (Wj) was proposed to construct an operating phase diagram on droplet formation and quantify the transition of droplet formation regimes. The effects of bipolar waveform parameters on droplet formation were systematically examined in terms of Wj, droplet velocity, and droplet diameter. Moreover, the printing of conductive microlines and micropatterns was precisely controlled under well-formed droplets. This study could support fully understanding the droplet formation dynamics during DOD inkjet printing of viscoelastic inks to guide generating desirable droplets of functional ink and improve the performance and function of inkjet-printed devices.

Inkjet Nozzle Failure by Heterogeneous Nucleation: Bubble Entrainment, Cavitation, and Diffusive Growth

Piezoacoustic drop-on-demand (DOD) inkjet printing is widely applied in high-end digital printing due to its unprecedented precision and reproducibility. Micron-sized droplets of a wide range of chemical compositions can be deposited; however, the stability of piezoacoustic DOD inkjet printing can sometimes be compromised through the stochastic entrainment of bubbles within the ink channel. Here, bubble nucleation, translation, and growth are studied in an experimental silicon-based printhead with a glass nozzle plate using high-speed imaging that is triggered by changes in the ink-channel acoustics. It is found that impurities in the ink can trigger bubble nucleation upon their interaction with the oscillating meniscus. Cavitation inception on a dirt particle during the rarefaction pressure wave is identified as a second mechanism for bubble formation. The acoustic driving pressure within the ink channel, and its change upon bubble nucleation, are obtained from a fit of a Rayleigh-Plesset-type bubble-dynamics equation to the measured time-resolved radial dynamics of the bubble. The measured decrease in channel resonance frequency after bubble entrainment results in a 24% increased ink-jet length. The nucleated bubbles translate toward the ink-channel walls due to acoustic radiation forces and ink streaming. The convective ink flow is characterized using high-speed particle-tracking velocimetry. The vortical flow near the oscillating meniscus is shown to trap the impurities, thereby increasing the particle-to-meniscus interaction probability and, correspondingly, the bubble-entrainment probability.

Characteristics of drop-on-demand droplet jetting with effect of altered geometry of printhead nozzle

As a precision micro-electromechanical actuator, the geometry of drop-on-demand (DoD) printhead nozzle could be altered resulting from the accumulated manufacturing tolerances (AMT) and partial nozzle clogging (PNC) which largely influences the droplet jetting dynamics. To explore the effect of altered nozzle geometry on the DoD droplet formation characteristics, a three-dimensional (3D) multi-relaxation-time (MRT) lattice Boltzmann (LB) model coupled with nonideal nozzle plate wettability is presented to handle the complex droplet jetting process. For typical Z=11.57, with the hydrophobic nozzle plate, the velocities of final droplet are increased with the nozzle volume decreasing θN=49° and PNC. The non-ideal hydrophilic nozzle plate could eliminate the effect of altered nozzle geometry which exhibits the identical trajectories of droplet jetting. As Z number increasing to Z=19.8, the overall velocities of liquid filaments and resulting droplets are increased considerably. However, the effect of AMT decreases the velocity of filament tail and the recombination of satellite and main droplets could not occur for θN=49° which is undesirable for DoD inkjet printing. For case of PNC, the leftward deviation of recombined droplet is increased for the non-ideal hydrophilic nozzle plate and large Z number which greatly deteriorates the droplet jetting directionality.

Influence of Z number and Pulse Voltage on Drop-on-Demand (DOD) Inkjet Printability

Inkjet printing has been applied in manufacturing structural and functional materials for decades. There are two kind of methods known as continuous inkjet (CIJ) printing and drop-on-demand (DOD) inkjet printing.[1] In DOD inkjet printing, drops are generated only when a drop needed by producing a pressure pulse in a chamber filled with inks. And before drop generation, the inkjet printing head will be moved to the desired location to locate the drop in a precise position. DOD inkjet printing is a method that directly places materials on demand, which saves the required raw materials and reduces the printing steps. As a consequence, DOD inkjet printing saves more time with lower waste consumption during production than CIJ printing and the equipment has a smaller footprint.DOD inkjet printing can be divided into two methods by which the pressure pulse is generated followed by drop ejection: thermal DOD inkjet printing and piezoelectric DOD inkjet printing. In piezoelectric DOD inkjet printing, the pressure pulse is produced by the mechanical actuation of the chamber walls.[2] When a voltage is applied, the piezoelectric material changes shape, which generates a pressure pulse in the fluid forcing a droplet of ink from the nozzle. It is important to know the inkjet printable range to generate accurate and repeatable drops. Fromm had defined ink printability in drop on demand (DOD) printing using a dimensionless Z number which related to the physical properties of the inks.[3] However, it is still not agreed whether there is a precise Z number range for inkjet printability and not known whether the range varies using different actuating pulses.The goal of our study is to find out the detail relationship between the ink properties and Drop-on-Demand inkjet printing printability and explore whether the printable Z number range change with actuating pulses and different kind of printheads.Here we investigate the influence of Z number and pulse voltage on printability using two inkjet printheads (10 pl Dimatix and 80 &#x3BC;m MicroFab). We have used 10 model inks made from solvent mixtures of ethylene glycol, diethylene glycol and distilled water. A range of actuating pulse voltages has also been studied. We found that the printable Z number range changes with the pulse voltages applied on inkjet printing. When increasing pulse voltage to print the same ink, it becomes printable under low pulse voltage and flying slow in the air and then printing well until at a certain voltage satellites forms and more satellites form when further increasing the pulse voltage. We also found that the printable voltage range is slightly different among inks with Z &lt; 8. Under higher pulse voltages, it is possible to get single droplets with Z &lt; 4, but inks with Z &lt; 4 are printed out with some satellites. However, accurate and stable drops without satellites could be formed using inks of Z &lt; 4 under lower voltages and it is not printable for inks of Z &lt; 4 when printed under lower pulse voltages. These results could give an explanation of the different Z number range shown in different researches published when they using different printheads and pulse voltages.

Controlling micro ceramic patterns via multiple/sequential drop-on-demand inkjet printing of dilute colloidal suspensions

Drop-on-demand (DOD) inkjet printing has great potential for fabricating miniature ceramic devices that are currently constructed by more complicated, time consuming, and costly procedures. In this study, micro La0.6Sr0.4Fe0.8Co0.2O3 (LSFC) patterns are crafted via DOD inkjet printing. A dilute solid-solvent colloidal ink suspension composed of LSFC, a common solid oxide fuel cell (SOFC) cathode material, suspended in α-terpineol solvent, was printed with multiple, sequential inkjet passes. Critical process parameters were identified and tuned to achieve acceptable layer to layer deposition accuracy. Micro 0-D dots and micro 1-D lines with x/y dimensions <100μm and z-axis dimensions <1μm were demonstrated. Addition of ethyl cellulose to the ink resulted in unique ‘volcano’ features which may benefit miniature SOFCs with a density shift between the feature’s center and ridge.

Particle Fabrication Using Inkjet Printing onto Hydrophobic Surfaces for Optimization and Calibration of Trace Contraband Detection Sensors.

A method has been developed to fabricate patterned arrays of micrometer-sized monodisperse solid particles of ammonium nitrate on hydrophobic silicon surfaces using inkjet printing. The method relies on dispensing one or more microdrops of a concentrated aqueous ammonium nitrate solution from a drop-on-demand (DOD) inkjet printer at specific locations on a silicon substrate rendered hydrophobic by a perfluorodecytrichlorosilane monolayer coating. The deposited liquid droplets form into the shape of a spherical shaped cap; during the evaporation process, a deposited liquid droplet maintains this geometry until it forms a solid micrometer sized particle. Arrays of solid particles are obtained by sequential translation of the printer stage. The use of DOD inkjet printing for fabrication of discrete particle arrays allows for precise control of particle characteristics (mass, diameter and height), as well as the particle number and spatial distribution on the substrate. The final mass of an individual particle is precisely determined by using gravimetric measurement of the average mass of solution ejected per microdrop. The primary application of this method is fabrication of test materials for the evaluation of spatially-resolved optical and mass spectrometry based sensors used for detecting particle residues of contraband materials, such as explosives or narcotics.

Electric field-assisted droplet formation using piezoactuation-based drop-on-demand inkjet printing

Droplets with diameters from a few to hundreds of micrometers have found increasing applications in various fields. For inkjet printing, there is always a great need to control and reduce the droplet size for a given nozzle diameter and print viscous fluids by avoiding clogging. This study investigates the electric field-assisted droplet formation process under piezoactuation-based drop-on-demand (DOD) inkjet printing. For better control of droplet monodispersity, the Taylor cone is intentionally suppressed to avoid undesirable satellite droplets. The droplet formation process of deionized water is investigated, and some main conclusions are drawn as follows: (1) with an increase of applied voltage, the droplet velocity increases and the droplet size decreases, (2) the pinch-off location may be different depending on the applied voltage; and (3) the combination effect of the electric field and meniscus oscillation can be utilized to significantly reduce the droplet diameter to less than one-fifth of the orifice diameter. The electric field also demonstrates its capability in facilitating the DOD inkjet printing of high-concentration cell-alginate suspensions.

Design and Implement of a Low Cost Drop-on-Demand Inkjet Printing System

Nowadays, drop-ondemand inkjet printing technology has shown its potential in many fields. This paper presents designing and implementing of a low cost drop-ondemand inkjet printing system. Inkjet printing system can be divided into four parts, and back pressure control system and droplet observation system are two key components, both of which are described in details. In order to have a further control of accuracy and stability of the system, this paper discusses the parameters designed in the system. In pressure control system, the designed system has higher accuracy compared with the Microfabs product. Images can be taken through CCD camera instead of ultra-high-speed camera by using droplet observation system. Some experiments also have been done to verify the feasibility of the device. Accuracy of pressure control, stability of the system and reproducibility of inkjet process can be verified from the experiment.

Toward better printing quality for a drop-on-demand ink-jet printer: improving performance by minimizing variations in drop properties

Drop-on-demand (DoD) ink-jet printing is an efficient technology for depositing picoliter drops on various printing surfaces. DoD technology is compatible with various liquids and does not require contacting the printing media. DoD inkjet printing combines several advantages including high speed, quiet operation, and compatibility with a variety of printing surfaces. Moreover, DoD printing can make patterns without any additional lithographic process. Ink-jet printing can reduce the number of processing steps compared to conventional patterning processes, which results in a lower production cost. Therefore, DoD ink-jet technology is applied in many engineering and scientific applications (see Figure 1), such as the formation of the conductive tracks for printed circuit boards, color filters in flat panel displays and plasma displays, polymer light-emitting diode displays, organic transistors, and the construction of DNA microarrays [1]-[5].

Polymer inkjet printing: Construction of three-dimensional structures at micro-scale by repeated lamination

Solution-based, direct-write patterning by an automated, computer-controlled, inkjet technique is of particular interest in a wide variety of industrial fields. We report the construction of three-dimensional (3D), micropatterned structures by polymer inkjet printing. A piezoelectric, drop-on-demand (DOD) inkjet printing system and a common polymer, PVA (poly(vinyl alcohol)), were explored for 3D construction. After a systematic preliminary study with different solvent systems, a mixture of water and DMSO was chosen as an appropriate solvent for PVA inks. The use of water as a single solvent resulted in frequent PVA clogging when the nozzles were undisturbed. Among the tested polymer ink compositions, the PVA inks in a water/DMSO mixture (4/1 v/v) with concentrations of 3 to 5 g/dL proved to be appropriate for piezoelectric DOD inkjet printing because they were well within the proper viscosity and surface tension range. When a dot was printed, the so-called ‘coffee-ring effect’ was significant, but its appearance was not prominent in line printing. The optimal polymer inkjet printing process was repeated slice after slice up to 200 times, which produced a well-defined, 3D micro-patterned surface. The overall results implied that piezoelectric DOD polymer inkjet printing could be a powerful, solid-freeform, fabrication technology to create a controlled 3D architecture.

Immobilization of Biomolecules on Poly(vinyldimethylazlactone)-Containing Surface Scaffolds

We describe the successful development of a procedure for the step-by-step formation of a reactive, multilayer polymer scaffold incorporating polymers based on 2-vinyl-4,4-dimethylazlactone (VDMA) on a silicon wafer and the characterization of these materials. Also discussed is the development of a procedure for the nonsite specific attachment of a biomolecule to a modified silicon wafer, including scaffolds modified via drop-on-demand (DOD) inkjet printing. VDMA-based polymers were used because of their hydrolytic stability and ability of the pendant azlactone rings to form stable covalent bonds with primary amines without byproducts via nucleophilic addition. This reaction proceeds without a catalyst and at room temperature, yielding a stable amide linkage, which adds to the ease of construction expected when using VDMA-based polymers. DOD inkjet printing was explored as an interesting method for creating surfaces with one or more patterns of biomolecules because of the flexibility and ease of pattern design.