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

Modeling of bias-induced changes of organic field-effect transistor characteristics

Three-dimensional (3D) bioprinting techniques, developed over the past two decades, have the potential to fabricate living, patient-specific tissues and organs for use in regenerative medicine (Kesti et al. 2016). Inkjet-based bioprinting is one of the oldest yet promising technologies, which combines the solid freeform fabrication process and precise cell placement in 2D and 3D. Typically, inkjet printing takes digital data of an image or character from a computer and reproduces it on to a material or substrate using ink drops in a noncontact mode (Mohebi and Evans 2002). In addition to its wide application in automation office tool, it has also been widely used in microengineering for printing electronic materials (Sirringhaus et al. 2000). Inkjet printer deposits controlled volume of ink in a layer-by-layer fashion to predefined locations on successive layers to form a 3D construct (Xu et al. 2008). Drop-on-demand (DOD) printers, a commonly used inkjet printers, are used for biological and nonbiological applications. The idea of printing of biological substances was introduced by Klebe after using HP thermal DOD inkjet printer to deposit collagen and fibronectin in 1988 (Klebe 1988). Later, Thomas Boland customized the thermal inkjet printer for printing living cells in a viable state (Wilson and Boland 2003). After this, scientists have made great progress in patterning molecules such as DNA, depositing proteins (Eric et al. 2009, Ilkhanizadeh et al. 2007, Miller et al. 2006), and printing tissues and organs by inkjet printing (Okamoto et al. 2000). The current focus of inkjet bioprinting is fabrication of 3D structures with clinically significant heights to extend its effectiveness in the direction of clinical applications. In this chapter, we discuss about the principle of inkjet bioprinting technology, types of inkjet printers in use, materials used for printing, and the critical parameters involved in this technique. Then, challenges associated with techniques and the future perspectives are also discussed.

In the search for efficient methodologies focused on up scaling production of low cost functional ceramic oxides, the implementation of Chemical Solution Deposition (CSD) in combination with drop on demand (DoD) inkjet printing technology is a challenge in materials science. When simple additive processing is implemented in continuous reel to reel systems with novel low-cost materials, the potential to further decrease the production costs of the whole manufacturing process is immense.Sets of parallel YBa2Cu3O7−x (YBCO) stripes, 250 nm thick and 150 μm wide, with critical current densities (Jc) of about 1.1 MA/cm2 at 77K and self field are obtained.On the other hand, different designs of magnetoresistive La0.7Sr0.3MnO3 (LSMO) devices with electrical resistances in the range of 10 KΩ including the contact pads, are drawn onto LaAlO3 (LAO) and SrTiO3 (STO) single crystals. We particularly investigate different strategies to increase pattern resolution and accuracy. Preliminary morphological and electrical characterizations of the device on cheaper amorphous, polycrystalline and textured substrates are presented.Therefore, this paper gives a summary of functional ceramic oxides patterning by combining CSD and inkjet printing methodologies onto different single crystal, polycrystalline and textured substrates. The present work demonstrates a powerful method of fabricating multifilamentary YBCO patterned coatings for low losses coated conductors (CC's) and LSMO magnetoresistive analog encoders for position sensing.

This chapter introduces the fundamental concepts necessary to understand polymers in inkjet formulation: molecular weight, their solution properties and their behaviour under flow. The formulation challenges of printing high molecular weight polymers arising from these flow behaviours are introduced along with the degradation reactions occurring in both drop on demand (DOD) and continuous inkjet (CIJ) systems for synthetic polymers and naturally occurring polymers showing tertiary structure.

A process combining conventional photolithography and a novel inkjet printing method for the manufacture of high sensitivity three-dimensional-shape (3DS) sensing patches was proposed and demonstrated. The supporting curvature ranges from 1.41 to 6.24 × 10−2 mm−1 and the sensing patch has a thickness of less than 130 μm and 20 × 20 mm2 dimensions. A complete finite element method (FEM) model with simulation results was calculated and performed based on the buckling of columns and the deflection equation. The results show high compatibility of the drop-on-demand (DOD) inkjet printing with photolithography and the interferometer design also supports bi-directional detection of deformation. The 3DS sensing patch can be operated remotely without any power consumption. It provides a novel and alternative option compared with other optical curvature sensors.

Performance Improvement of Professional Printing Systems: from theory to practice Markets demand continuously for higher quality, higher speed, and more energy-efficient professional printers. In this thesis, control strategies have been developed to improve the performance of both professional inkjet and laser printers. Drop-on-Demand (DoD) inkjet printing is considered as one of the most promising printing technologies. It offers several advantages including high speed, quiet operation, and compatibility with a variety of printing media. Nowadays, it has been used as low-cost and efficient manufacturing technology in a wide variety of markets. Although the performance requirements, which are imposed by the current applications, are tight, the future performance requirements are expected to be even more challenging. Several requirements are related to the jetted drop properties, namely, drop velocity, drop volume, drop velocity consistency, productivity, and reliability. Meeting the performance requirements is restricted by several operational issues that are associated with the design and operation of inkjet printheads. Major issues that are usually encountered are residual vibrations in and crosstalk among ink channels. This results in a poor printing quality for high-speed printing. Given any arbitrary bitmap, the main objective is to design actuation pulses such that variations in the velocity and volume of the jetted drops are minimized. Several model-based feedfoward control techniques using an existing model are implemented to generate appropriate input pulses for the printhead. Although the implementation of the model-based techniques shows a considerable improvement of the printhead performance compared with the current performance, further improvements are still necessary. We observe that besides the pulse shape the state of the ink surface at the nozzle plate (speed, position) at the start of the pulse influences the drop velocity considerably. This state at firing depends also on previous pixels in the bitmap of the image. Consequently, any pulse design has to guarantee almost the same initial state when firing a drop. Based on these facts, a model-free optimization scheme is developed to minimize the drop velocity variations taking into account the bitmap information. Experimental results show the effectiveness of the optimized pulses. Laser printing systems are highly depending on the appropriate combination of several design factors so as to become functional in a desired working range. The physical printing process involves multiple temperature set points at different places, precise electro-magnetic conditions, transfer of toner through certain pressures and layouts, and many other technical considerations. In the laser printing system there are several challenging issues and unknown disturbances. They originate from different sources, such as the printer itself (unknown phenomena appear, disturbances that are not foreseen, wear, contamination, failures, bugs), the environment of the system (power supply variations, temperature, humidity, vibrations), and the printing media (weight, coating, thermal properties, humidity characteristics, and initial temperature). These issues have a negative effect on the stability and performance of the laser printing system. The objective is to design a control scheme to achieve printing quality requirements and a high productivity. Good printing quality means that the fusing temperature should track a certain reference signal at different operating conditions. Based on the printing system behavior, we propose two different control schemes to cope with the large parameter variations and disturbances, namely, a Model Reference Adaptive Controller (MRAC) and a nonlinear (scheduled) observer-based output feedback control scheme. Both control techniques yield considerable performance improvements compared with the present industrial controller.

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.

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.

Ecole Polytechnique Federale de Lausanne, 1015 Lausanne – Switzerland ABSTRACT: The technology transfer of highly efficient solar cell concepts (i.e. passivated emitter and rear cell PERC) to industry can help reduce their production cost. This work appraises three different industrial approaches for the technology transfer and a conventional processing with a fair comparison. A significant improvement compared to conventional processing was obtained. All advanced approaches lead to an increase in open circuit voltage and short circuit current. This testifies to the benefits of improved passivation of the rear surface and a bettered light trapping. The optimal processing window for the advanced approaches has lower fill factor than the conventional processing. However, the reduction does not result in lower conversion potential. Finally, the PERC type devices deliver a significant increase of more than 0.4 % absolute in conversion efficiency. The structure which proved best was based on laser fired contacts (LFC). A maximum efficiency of 17.0 % has been achieved on 1.8 Ωcm multi-crystalline silicon. Keywords: PERC, inkjet, laser ablation, multi-crystalline silicon. 1. INTRODUCTION In recent published studies [1], a roadmap towards lower production cost was delineated. It features higher production volumes, higher efficiency silicon solar cells with respect to conventional present technology and lower silicon wafer thickness. This work addresses the two latter challenges by proposing optimized process sequences. Furthermore, these sequences are applied to multi-crystalline silicon (mc-Si), which has a lower intrinsic production cost. The increased ratio of surface to volume draws the attention to surface passivation. The work will detail different options to locally contact the base through the passivation on the back surface. The adaption of conventional screen printing techniques highlights the value of the here investigated technology transfers for the industry. Different local contacting techniques were already presented in [2-4]. However, differences, especially in back surface passivation and starting material, hindered their direct comparison. This work aims to test each advantageous for the light trapping [7] and for an enhanced passivation potential [8].

Printed Electronics is moving from R&amp;D to Manufacturing in a wide range of Commercial Markets. It is certainly not living up to the original hype but like many successful new technologies it is finding more and more novel applications. Many of these applications utilize more than one printing technologies and one of these is ink jet printing. Color OLED display panels, antennae, solar cells, fuel cells, organic transistors, conductors &amp; passive components, sensors, board games, smart surfaces and microelectronic packaging are some of the emerging applications that indicate that ink jet technology is a key enabler for printable electronic manufacturing. Most of these applications require the printing of polymers or polymer solutions: both conductive and semiconductive polymers; conductor inks; dielectrics; light emitting polymers; color filters and specialty bio-materials. Many of these applications are enabled by developments of nanoparticle and micro-size particle inks.&#x2022; In this paper we will:&#x2022; Present a brief status of Printed Electronics&#x2022; Briefly introduce ink jet technology for printed electronics;&#x2022; Review specific technical applications carried out at MicroFab for the past 20 years;&#x2022; Discuss the key technology developments required for an ink jet printing production platforms; and&#x2022; Review the key infrastructure issues and gaps in the technology that have to be resolved.

Investigation of ink-jet printing of poly-3-octylthiophene for organic field-effect transistors from different solutions

One of the challenges in inkjet technology is the reduction of residual vibration and crosstalk that can result in the appearance of satellites and ligaments in the produced droplets, which affects the overall printing quality. This study evaluated the print quality produced by comparing basic waveform with several actuating waveforms, particularly in the application of the grayscale method or the multi-pulse-ejection method. Print quality was compared using a microscope to evaluate the appearance of ejected droplet on a printing surface. This study measured aspect ratio to illustrate the circularity of the droplets. Based on the findings in this study, the waveform design with adjustments made to the rear wave from the preliminary vibration is proved effective in improving print quality. The average of aspect ratio obtained approached 1, means almost perfect circular, which was 0.997, with the lowest standard deviation of 0.0151.

Piezo-acoustic drop-on-demand (DOD) inkjet printing is widely applied in high-end digital printing due to its unprecedented precision and reproducibility. However, the stability of piezo-DOD inkjet printing can sometimes be compromised through the stochastic entrainment of bubbles within the ink channel. The acoustically driven air bubble modifies the ink channel acoustics, and conversely, the modified ink channel acoustics influences the bubble dynamics. Here, we measure the acoustic eigenfrequency of a MEMS based silicon ink channel as a function of the bubble size. The eigenfrequency was measured using a pulse-echo system and the bubble size using a short-wave infrared imaging setup. We show that the measured eigenfrequency increases when an air bubble is entrained. Surprisingly, the ink channel resonance frequency plateaus at total bubble volumes larger than 10 pl. Moreover, it was found that at a constant total bubble volume, the resonance frequency increases with the number of entrained bubbles. We show that both experimental observations can be quantitatively explained from a simple lumped element model (LEM) comprising the ink channel Helmholtz resonator coupled to the bubble mass-spring system. The results of the LEM model were validated using a full numerical model of the coupled ink channel—bubble system.

The drop-on-demand (DOD) inkjet printing technology has been widely used in many fields and several types of droplet generators are developed. This paper presents the design, fabrication and tests of a piezoelectric bend mode drop-on-demand inkjet printhead with interchangeable nozzle. A disk-type PZT is actuated to push the liquid out of inkjet printhead by a function generator, and a droplet is formed because of surface tension. The interchangeable nozzle design enables the same printhead to be fitted with nozzles of different orifice size, thus a clogged nozzle can be easily removed for cleaning or replacement. An experimental platform for micro-droplet jetting is built in this paper. The droplet formation is recorded by a CCD camera as pictures, which can be used to measure the droplet dimension. The experiments are carried out by using the self-developed bend mode piezoelectric inkjet printing system. The influence of the drive parameters on the droplet quality is also studied by dispensing water.

Submicron sized silver powder was prepared from AgNO3 using a chemical-reduction method. A spherical silver power exhibiting an average particle size distribution of 0.2–0.4 μm and an excellent dispersibility was achieved and applied to the inkjet printing process. A drop-on-demand (DOD) inkjetting system was used to print the silver particles suspended in a terpineol solvent. Through sintering at 300 °C, the size of the particles adjacent to the borderline of droplets were gradually increased and necking was observed between the droplets. Alternatively, the substrate for the particles could be heated to a lower temperature, and the sintering process of the conducting line was completed by the application of a laser beam. Increase in the laser power reduces the resistivity of the line. Through microstructure analysis, the necks between droplets were sintered at a specific energy density (ψ = 0.0398 J mm−3). The conducting lines were soldered and of a larger aggregation, between which a discontinuous micro-crack was observed. This was attributed to the surface tension effect and shrinkage during solidification. Influence of the densification parameters on resistivity was significant.