Inkjet Printhead Research Articles

Investigation of CMOS Multiplexer Jet Matrix Addressing and Micro-Droplets within a Printhead Chip.

In this study, we demonstrate and investigate a new droplet injection design. We create a thermal inkjet (TIJ) printhead using an application-specific integrated circuit system and bulk micromachining technology (microelectromechanical systems). We design inkjet printhead chips with a new structure and investigate their properties. For the new structure, the integration of complementary metal-oxide-semiconductors (MOSs) and enhancement-mode devices, as well as power switches and a TIJ heater transducer, enables logic functions to be executed on-chip. This capability is used in the proposed design to address individual jets with even fewer input lines than in matrix addressing. A high number of jets (at least 896) can be addressed with only 11 input lines. E1 (Enable 1) and E2 (Enable 2) are set up dependently, and they have the ability to reverse their signals in relation to each other (i.e., if E1 is disabled, E2 is enabled and vice versa). The E1 and E2 signals each service 448 jets. If one of the MOSs is turned on, then it corresponds to a power line with a similar function. If an addressing gate terminal of the other MOS has a discharge action, then we can control a different heater to generate heating bubbles in the jet inks. The operating frequency for addressing these measurements is 18 kHz in normal mode, 26 kHz in draft mode, and 16 kHz in best mode.

Where next for industrial digital printing?

At present, there are two dominant technologies for the digital deposition of liquids: inkjet and valvejet. Both have very different ejection mechanisms and each has very different technical specifications. As a result, they are exploited in very different applications. Inkjet is used where high image resolution and small droplets are required, leading to its adoption in surface decoration, digital document presses and the like. [1] The construction of inkjet printheads, and the fundamental physics of droplet formation, prevent its use with viscous or sedimenting inks In comparison, valvejet is a far cruder technology as the droplets are much larger, the firing rate is lower and the nozzle density is low. Array versions of valve-jet were initially developed for carpet decoration and it is best suited to applications where the print resolution doesn't need to be high. Unlike inkjet, valvejet printheads are capable of processing viscous fluids. There is thus a large capability-gap between inkjet and valvejet. As a result, in a wide range of applications where there is a demand for accurate digital deposition of viscous materials, no solution is readily available. In this paper, we show that TTP's Vista Inkjet technology is ideally suited to many of these applications, and provide an initial estimate of the market demand for such a solution.

A Thermal Ink-Jet Printer Head Prototype With Full Carbon Based Microbubble Generator

This paper presents the development of a novel thermal ink-jet printer head prototype using full carbon-based microbubble generators with carbon nanotubes as heating elements and graphene as electrodes. Meanwhile, each microbubble generator is equipped with a carbon nanotube sensor to real-timely probe the temperature of its surrounding micro-environment. With an array of microbubble generators and sensors fabricated on quartz glass, as well as a microfluidic structure constructed by the micromachined silicon, the printer head prototype is formed by an anodic silicon-glass bonding process with several scattered graphene film flakes as medium. Droplet ejection with volume as tiny as ~0.03 pl corresponding to a very high spatial resolution of >2000 dpi driven by two microbubble valves is demonstrated by the printing unit in the prototype. Increasing the input power cannot only speed up the bubble nucleation and growth, but also improve the utilizing efficiency of electric heating energy. The experimental detected temperature variation in the printing unit reveals its nonlinear heat convection property by comparison with the theoretical calculation by finite-element analysis. [2017-0048]

Operational Design of Magnetostrictive Inkjet PrintHead

This paper presents the redesign of the first magnetostrictive inkjet printhead (MagJet). The redesign includes the structural redesign and operational redesign. After completing the process successfully, the redesigned MagJet is subjected to testing. The effect of backpressure from a commercial syringe pump is evident. The operating frequency with backpressure reaches up to 1.5 kHz, although that without backpressure is 650 Hz. The droplet size at a frequency of 800 Hz is about 53 μm, less than half of the nozzle size. It can be concluded that various droplets can be made by combining frequency with a proper flow rate. Backpressure prevents the MagJet from air inclusion in the nozzle, so continuous ejection of the droplets are possible.

Fabricating method of SU-8 photoresist conical nozzle for inkjet printhead

ABSTRACTA novel conical nozzle fabrication method for piezoelectric inkjet printhead is proposed based on the microelectromechanical system technology. By optimizing the exposure gap, exposure dose, postexposure bake (PEB), and development time, the SU-8 conical nozzle was fabricated. After thermal bonding with an open chamber, the piezoelectric inkjet printhead chamber was formed. The results show that the optimum SU-8 conical nozzle can be fabricated by applying exposure dose of 105 mJ/cm2, exposure gap of 50 µm, PEB temperature of 65°C, PEB time of 10 min, and development time of 210 s. The final size of optimum conical nozzle is the large aperture of 30.46 ± 1.17 µm, small aperture of 20.34 ± 1.42 µm, and nozzle height of 45.38 ± 1.02 µm.

Punctuated Equilibrium and Knowledge Flow: Toward a New Understanding of Technological Change

This paper aims to enrich our understanding of punctuated equilibrium in technological change, which argues that technology evolves through a relatively long period of stability and continuity that is interrupted and punctuated by a relatively short burst of discontinuous, radical change. Most past literature has paid little attention to the embedded knowledge flow in technological change. To address this gap, a conceptual framework is exhibited to summarize our idea. The key-route main path analysis approach is used to construct the knowledge flow in punctuated equilibrium. Empirically, the thermal inkjet printhead is chosen as the research target, and patent data from USPTO were collected and used. We found that thermal inkjet printheads experienced three distinct phases of technological continuities, each of which is a cyclic divergent-convergent knowledge flow initiated by a breakthrough centering around a significant, prioritized technical problem. One knowledge cycle is to shape a distinct knowledge...

Process for fabricating microactuator membranes of piezoelectric inkjet print head using multi‐step deep reactive ion etching process

As part of an effort to develop piezoelectric inkjet print head (PIPH), a process for fabricating its Si-cups and actuator membranes of multi-layered structures was investigated. The manufacture of this device was enabled by the use of deep reactive ion etching (DRIE). Based on that, multi-step DRIE process was proposed to etch the multi-layered actuator membranes on silicon on insulator wafers. Due to the appropriate parameters of the etching process, undesirable effects, such as Si grasses, notching effect of Si-cups and the bowing formation on the sidewalls, were also avoided. The way to eliminate the over-etching of SiO2 membranes by controlling the appropriate platen power and process duration simultaneously was also presented. High quality PIPH actuator membranes were finally obtained, making great contributes to the successful inkjet test.

Silver-based reactive ink for inkjet-printing of conductive lines on textiles

Silver is the material of choice for printed electronics. However, dispersed silver particles can block the fine nozzles of an inkjet print head and after printing the patterns have to be sintered at elevated temperatures to provide high conductivity. In this work we investigated and optimized the printing of a reactive silver ink which contains silver in complexed form, therefore avoiding disadvantages of particle dispersions. After printing the complexed silver is transferred into metallic by evaporating the complexing ligands at 50°C. The ink contains around 11% silver and has a surface tension of 26mNm−1. It is stable for at least 1month at room temperature and for at least 3months at 2–8°C. The ink was tested on several substrates and an application on textile is shown. The inkjet printed electronic circuit paths on the fabric withstand washing tests, moisture, and heat as well as crumpling.

A waveform design method for high DPI piezoelectric inkjet print-head based on numerical simulation

In order to increase the Dots Per Inch (DPI) of the piezoelectric inkjet print-head, the width and length of the pressure chamber have become much smaller. This makes some previous waveform design methods no longer suitable for the design of high DPI piezoelectric inkjet print-head. In this paper, a new waveform design method based on numerical simulation for high DPI print-head is proposed. Different parameters of the unipolar trapezoidal waveform were optimized using the multi-physics simulation software COMSOL to acquire the optimal waveform for good quality jetting. And meniscus motion at the nozzle exit was measured to predict the jetting behavior of print-head and verify the simulation results. When the high DPI print-head was actuated by the optimized waveform with the rising time tr = 3 µs, dwelling time td = 16 µs, and falling time tf = 3 µs, the high DPI piezoelectric inkjet print-head was continuous injection.

Soluble Metal Oxo Alkoxide Inks with Advanced Rheological Properties for Inkjet-Printed Thin-Film Transistors.

Semiconductor inks containing an indium-based oxo alkoxide precursor material were optimized regarding rheology requirements for a commercial 10 pL inkjet printhead. The rheological stability is evaluated by measuring the dynamic viscosity of the formulations for 12 h with a constant shear rate stress under ambient conditions. It is believed that the observed superior stability of the inks is the result of effectively suppressing the hydrolysis and condensation reaction between the metal oxo alkoxide precursor complex and atmospheric water. This can be attributed to a strong precursor coordination and the resulting reduction in ligand exchange dynamics of the solvent tetrahydrofurfuryl alcohol which is used as the main solvent in the formulations. It is also shown that with a proper selection of cosolvents, having high polar Hansen solubility parameter values, the inks drop formation properties and wettability can be fine-tuned by maintaining the inks rheological stability. Good drop jetting performance without satellite formation and high drop velocities of 8.25 m/s were found with the support of dimensionless numbers and printability windows. By printing single 10 pL ink dots onto short channel indium-tin-oxide electrodes, In2O3 calcination at 350 °C and a solution-processed back-channel protection, high average saturation mobility of approximately 10 cm2/(V s) are demonstrated in a bottom-contact coplanar thin-film transistor device structure.

Study of the viability of manufacturing ceramic moulds by additive manufacturing for rapid casting

Additive manufacturing (AM) has been considered one of the best processes to manufacture components with complex geometries, many times impossible to achieve with traditional processes, such as moulds with conformal cooling. Binder Jetting (BJ) technology uses an ink-jet printing head that deposits an adhesive liquid, layer by layer, to bind a powder material that can be ceramic, metallic, or other, which allows manufacturing parts to be used in research and industry.The aim of this work is to study the possibility of using BJ to produce plaster moulds for directly cast metallic parts at a lower cost than with metallic AM processes, using different types of infiltrates and post-processing parameters to improve the mechanical and thermal strength of moulds in order to be able to cast an aluminium alloy. The mechanical and thermal resistance of moulds with a thickness range of 2.5-4mm were analysed, as well as the surface roughness of metal samples, and compared with those obtained by traditional processes. Although all the moulds had good heat resistance during the casting, some did not have enough mechanical strength to withstand the metalostatic pressure, especially those with walls of 2.5 to 3.5mm.

Dynamics of wetting explored with inkjet printing

An inkjet printer head, which is capable of depositing liquid droplets with a resolution of 22 picoliters and high repeatability, is employed to investigate the wetting dynamics of drops printed on a horizontal plane as well as on a granular monolayer. For a sessile drop on a horizontal plane, we characterize the contact angle hysteresis, drop volume and contact line dynamics from side view images. We show that the evaporation rate scales with the dimension of the contact line instead of the surface area of the drop. We demonstrate that the system evolves into a closed cycle upon repeating the depositing-evaporating process, owing to the high repeatability of the printing facility. Finally, we extend the investigation to a granular monolayer in order to explore the interplay between liquid deposition and granular particles.

Construction of 3D cardiac tissue with patterned vascular structure by inkjet printer head

Construction of 3D cardiac tissue with patterned vascular structure by inkjet printer head

Fluid Micro-Reservoirs Array Design with Auto-Pressure Regulation for High-Speed 3D Printers.

Three dimensional (3D) printing technology is rapidly evolving such that printing speed is now a crucial factor in technological developments and future applications. For printing heads based on the inkjet concept, the number of nozzles on the print head is a limiting factor of printing speed. This paper offers a method to practically increase the number of nozzles unlimitedly, and thus to dramatically ramp up printing speed. Fluid reservoirs are used in inkjet print heads to supply fluid through a manifold to the jetting chambers. The pressure in the reservoir’s outlet is important and influences device performance. Many efforts have been made to regulate pressure inside the fluid reservoirs so as to obtain a constant pressure in the chambers. When the number of nozzles is increased too much, the regulation of uniform pressure among all the nozzles becomes too complicated. In this paper, a different approach is taken. The reservoir is divided into an array of many micro-reservoirs. Each micro-reservoir supports one or a few chambers, and has a unique structure with auto-pressure regulation, where the outlet pressure is independent of the fluid level. The regulation is based on auto-compensation of the gravity force and a capillary force having the same dependence on the fluid level; this feature is obtained by adding a wedge in the reservoir with a unique shape. When the fluid level drops, the gravitational force and the capillary force decrease with it, but at similar rates. Terms for the force balance are derived and, consequently, a constant pressure in the fluid micro-reservoir segment is obtained automatically, with each segment being autonomous. This micro reservoir array is suggested for the enlargement of an inkjet print head and the achievement of high-speed 3D printing.

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 μm 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 < 8. Under higher pulse voltages, it is possible to get single droplets with Z < 4, but inks with Z < 4 are printed out with some satellites. However, accurate and stable drops without satellites could be formed using inks of Z < 4 under lower voltages and it is not printable for inks of Z < 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.

Estimation of High Speed Sintered Nylon-12 Tensile Strength Using Visible Reflectance Spectroscopy

Additive Manufacturing (AM) refers to a class of manufacturing processes which produces three dimensional objects directly from 3D model data. A range of AM processes, such as fused deposition modelling and laser sintering are deemed slow compared to injection moulding, as they depend on point-to-point consolidation. In order to progress into high speed manufacturing, a novel process called the High Speed Sintering (HSS) process is currently being developed at the University of Sheffield.HSS is a powder bed fusion process which employs an inkjet print head to print a cross sectional image of an <fig position="float" id="s37_f.1"> <label>Figure 1</label> <caption>Key components in the High Speed Sintering (HSS) process</caption> <graphic mime-subtype="tif" xlink:href="Images\s37_f01.tif" xmlns:xlink="http://www.w3.org/1999/xlink"/> </fig> object in radiation absorbing material (RAM) onto a powder build bed.[1] The build bed is subsequently exposed to infrared radiation to promote selective sintering of RAM coated powder, leaving the surrounding powder to act as a support. Consolidation is obtained by adding a new layer of powder in between printing successive images to form a 3D object. The HSS process uses Nylon-12 as its standard material, and is suitable to use with a range of polymer powder, especially thermoplastics. An overview of the HSS process with its key components is illustrated in Figure 1 below.Previous research on HSS has focused on assessing the effect of infrared lamp level,[2] the addition of flow agent[3] and the greyscale value on the mechanical properties of parts. Few studies have been performed on non-destructive characterisation of polymer parts, either by using Differential Scanning Calorimetry (DSC)[5] or NIR spectroscopy for laser sintered parts[6] and rubber parts[7]. This project aims to propose a non-destructive method to estimate the tensile properties of HSS Nylon-12 parts. Previous research based on the “greyscale level” suggested a correlation between the input ink dithering level during sintering process and the resultant parts tensile properties, however this method is not widely applicable across all inkjet print heads due to the difference in specifications. Spectroscopy method has never been used to assess parts made by the high speed sintering process and is advantageous as it quantifies an output grey level.In this contribution, an overview of the HSS processing of Nylon-12 powder will be provided. Reflectance spectroscopy will be performed on manufactured parts and the results compared with actual tensile tests. The correlation between HSS Nylon-12 parts reflectance values and their corresponding ultimate tensile strength values will be presented.

Meniscus Motion Inside A DoD Inkjet Print-Head Nozzle

A new study of the jetting performance for drop-on-demand (DoD) inkjet print heads investigated meniscus motions inside the transparent nozzles of MicroFab inkjet print heads. A composite image representation of the observed meniscus motions, imaged at high resolution using a spark flash light source, was developed for our subsequent analyses of the influences of drive voltage and pulse dwell time and also the ink properties. At higher drive voltages a slow damped refill (following de-pinning of the meniscus from the very edge of the nozzle exit) was also clearly observed. This and many other interesting phenomena were observed with the composite images: internal bubbles that progressed through the nozzle region over relatively long timescales, internal break-off of the jet from the meniscus surface, satellite formation and merging, and the contact line de-pinning not previously observed before..

Measurement of Inkjet Printhead Reliability by Detecting Every Single Droplet in Flight

Inkjet printing is adapted for many digital imaging systems including graphical, industrial and advanced manufacturing applications. Reliability was identified to be one of the key challenges for inkjet printheads due to their susceptibility to variations in temperature, ink consistency, debris or external vibration. Hence, lengthy tests with printouts on kilometers of papers are necessary to establish a measure of reliability, which is time-consuming and extends the development cycle for a given application. In this contribution a line-scan camera is used to observe all droplets from a printhead row in flight at full jetting frequency. This allows for the identification of missing droplets as a function of the printed image, external disturbances as well as the drive waveforms used and other print parameters. This provides a quantitative measurement not only of reliability but also of deviations in droplet velocity and trajectory in a laboratory environment. The paper discusses the necessary hard- and software approaches and details the necessity for various image transformations due to the challenges imposed by the illumination. Furthermore, we will present experimental data as well as speed benchmarks.

Refilling characteristics of high frequency piezo driven ink jet print heads

A piezo driven ink jet print head is in principle an open microfluidic system, there are no valves that control the direction of the flow. In order to avoid flooding of the nozzle plate at nozzle level a small under-pressure is maintained. In equilibrium the meniscus of the ink is retracted and pinned to the rim of the nozzle. This equilibrium is controlled by the surface tension of the ink and the setting of under-pressure controller. Operated at low frequencies, after droplet formation, there is ample time for the ink to return to the equilibrium state and to be ready for the next firing of a droplet. Driven at higher frequencies, in between droplets, there is no time to return to the equilibrium state and other mechanisms for refilling come into view. When the meniscus has retracted in the nozzle, the next pressure pulse needs to accelerate a relatively small amount of ink. Moreover the viscous drag in a partly filled nozzle is less compared to a completely filled nozzle. With a constant surface tension pressure, the Washburn equation learns that the refilling speed of a partly filled nozzle increases with decreasing filling of the nozzle. Both effects are supposed to cause that a print head driven at high frequency delivers enough fluid to nozzle to maintain droplet emission. In this paper this theoretical framework is extended by taken into account: <list list-type="bullet"> <list-item>• Droplet formation on the dynamics of the fluid motion,</list-item> <list-item>• Change of droplet volume at high frequencies,</list-item> <list-item>• Inertia effects due to the variable mass in the nozzle. A complete non-linear analysis will be outlined including:</list-item> <list-item>• Limitation of the capillary pressure; only close to the nozzle the capillary pressure becomes a linear function of the meniscus displacement, otherwise it is a constant,</list-item> <list-item>• The dependence of the viscous drag on the filling of the nozzle,</list-item> <list-item>• The effects of droplet formation,</list-item> <list-item>• Inertia effects due to the variable mass in the nozzle.</list-item> <list-item>• Calculations will be performed for a sample pump of which the dimensions are representative for a standard print head. Two inks will be investigated one with a viscosity of 0.01 Pa.s and another with a low viscosity equal to 0.002 Pa.s.</list-item> </list>The non-linear analysis will reveal many details of the fluid dynamics of the ink in a print head, including effects of surface tension, viscosity, droplet formation, pulse shape and repeat rate.

Refilling characteristics of high frequency piezo driven ink jet print heads

Refilling characteristics of high frequency piezo driven ink jet print heads