Ink-jet Process Research Articles

Colloidal particle assembly using piezoelectric inkjet printing of polystyrene colloidal ink formulations.

We report the feasibility of piezoelectric inkjet printing of colloidal dispersion inks for geometrical patterning to arrange colloids in desired locations. Polystyrene colloid (dia. = 3 μm) inks dispersed with thermally curable binder in organic solvents are explored for fundamental study on colloidal patterning. The inkjet printability of colloidal inks is systematically investigated with different ink formulations and inkjet process variables. In addition, in order to maintain the structural stability of colloidal patterns fabricated on the substrate from externally applied forces such as mechanical, chemical and thermal stimuli, thermally curable binder was formulated into the colloidal ink formulations.

Solution Processed Oxide Thin Film Transistors

We have developed thin-film-transistors (TFTs) manufactured by a solution processing of the gate insulators and the active material. Oxide insulators, such as aluminum oxide, hafnium oxide, or zirconium doped aluminum oxide represent a method to achieve high performance and low power consuming TFTs. Along with amorphous indium gallium zinc oxide ( a-IGZO), other oxide semiconductors have been studied. Solution processing offers the opportunity to test various materials quickly with low capital investment. We studied poly-crystalline materials, such as indium oxide (In2O3), and tin oxide (SnO2), or amorphous oxides such as indium zinc tin oxide (IZTO).We have developed inket-printed TFTs at the maximum process temperature of 300oC. Inkjet-printed polycrystalline InOx TFTs have mobilities of 60cm2/Vs, and were used in unipolar inverters. SnOx TFTs, show a dependence on the solution concentration, and the mobility can reach ~70cm2/Vs. On the other hand, amorphous IZTO TFTs showed the highest mobility of ~100cm2/Vs by the careful control of the inkjet process. References C. Avis and J. Jang, J. Mater. Chem., 21, 10649-10652, 2011C. Avis and J. Jang, Jap. J. Appl. Phys., 2011, 50, 01BG03, 2011C. Avis and Jin Jang, Electrochem. Solid-State Lett., 4, J9-J11, , 2011Y. G. Kim, C. Avis and J. Jang, ECS Solid-State Lett., 1, Q23-Q25, 2012C. Avis, Y. G. Kim, and J. Jang, J. Mater. Chem., 22, 17415–17420, 2012Y. G. Kim, C. Avis, and J. Jang, J. Disp. Tech., accepted, 2014Figure 1: transfer characteristics of IZTO TFT.

Microdrop generation and deposition of ionic liquids

Abstract

Improved electrical properties of zinc-tin oxide TFTs by inkjet process optimization

Inkjet printing process was optimized to improve the electrical properties of inkjet-printed zinc-tin oxide thin-film transistors. Among the process conditions evaluated, inkjet voltage and substrate temperature were found to be the key factors for obtaining uniform thin-films and good thin-film transistors. The optimization process with a jetting voltage of 60 V and substrate temperature of 50°C gave good electrical properties, such as a field-effect mobility of 5.11 cm2/V s, a threshold voltage of 2.83 V, a subthreshold slope of 1.33 V/dec, and an on-to-off current ratio of 108. The electrical properties of the inkjet-optimized TFTs were superior to those of the unoptimized inkjet TFTs. A positive bias stability was also investigated.

Interfacial sol–gel processing for preparation of porous titania particles using a piezoelectric inkjet nozzle

The aim of the present work is to apply the liquid–liquid interfacial crystallization using a piezoelectric inkjet nozzle to the sol–gel processing. The instillation process was compared with the batch process to elucidate the effectiveness of the inkjet technique on the liquid–liquid interfacial sol–gel processing. The effect of frequency and water concentration in titanium tetraisopoxide (TTIP) solution on titania particle properties was investigated for sol–gel processing with a piezoelectric inkjet nozzle. Titania particles produced by each process were calcined at 500°C. The crystal structure, morphology, pore size distribution and specific surface area of titania particles were evaluated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen physisorption measurement. The photocatalytic activity of titania particles was evaluated by the photodegradation of methylene blue solution under UVC light irradiation.Monodispersed titania particles could be produced by instillation sol–gel processing of hexane using a piezoelectric inkjet nozzle. Titania particles prepared at 1500Hz were spherical while titania particles prepared at 1000Hz and 3000Hz were non-spherical. The number of particulate fracture increased with water concentration in TTIP solution. The inkjet nozzle-mediated instillation processing was found to be a promising way to create porous titania particles with a high photocatalytic activity.

Geometric confinement of directly deposited features on hydrophilic rough surfaces using a sacrificial layer

It is challenging to achieve high definition for inkjet-printed features on hydrophilic rough surfaces. In this study, a spreading diameter of ~5 mm was observed for a 10 pL inkjet droplet when it impacted onto a hydrophilic rough surface. A new geometric confinement method was employed to facilitate a much higher inkjet printing definition in the range of ~50 μm. A layer of water-soluble polyacrylic acid (PAA) was spin-coated onto a hydrophilic rough surface and then inkjet patterned. Subsequently, the PAA was made water-insoluble by subjecting the sample to a heat treatment with temperatures above 170 °C. The change in solubility of PAA during the heat treatment is found to be a crucial factor, which enables the physical confinement of the subsequently inkjet printed aqueous-based droplets. The thickness of the spin-coated sample also plays a critical role in the effectiveness of the physical confinement. The effectiveness of the proposed approach was demonstrated with an inkjet patterning process, in which a dielectric layer of 200 nm SiN x on a textured silicon wafer was selectively etched using 10 pL inkjet-printed droplets resulting in a line width of ~75 μm. When using a 1 pL printhead, the etched line width was as fine as ~30 μm.

Low-temperature processing of inkjet-printed IZO thin-film transistors

Inkjet-printed indium-zinc oxide (IZO) thin-film transistors (TFTs) were prepared at a processing temperature of 200 °C for the first time. The formulation of the inkjet solution and the process optimization resulted in a mobility of 0.45 cm2/Vs, a threshold voltage of 7 V, an on-to-off current ratio of 105 and a subthreshold slope of 0.5 V/dec at the low annealing temperature of 200 °C, the best properties in the inkjet process thus far. The metal-oxide formation at 200 °C was confirmed by using X-ray photoelectron Spectroscopy. The bias stability of an inkjet-printed IZO TFT at 200 °C was also characterized.

A Simple, Scalable Process for the Production of Porous Polymer Microspheres by Ink‐Jetting Combined with Thermally Induced Phase Separation

Porous microspheres capable of delivering high payloads of biomolecules with suitable biodegradability and biocompatibility would be valuable in delivery systems to aid tissue regeneration. This study describes a facile, scalable technique to produce biodegradable porous microspheres by combining continuous ink‐jetting through a piezoelectric nozzle with thermally induced phase separation (TIPS). A selection of biomaterials is investigated to suit delivery in tissue engineering, the synthetic polyesters poly(lactic‐co‐glycolic acid) (PLGA), and poly caprolactone (PCL) and a natural polymer, gelatin. The parameters governing the microsphere production are determined experimentally and compared to theoretical predictions derived from the fluid mechanics and heat transfer during the ink‐jetting process. The microspheres produced have open interconnected pores with mean particle diameters of 80–200 μm and no significant skin region. The physical properties, such as the mean particle diameter, pore size, and surface area could be controlled by varying production parameters including the ink‐jetting pressure, nozzle height, and the size and oscillation frequency of the nozzle. The technique is demonstrated to successfully encapsulate a model hydrophobic molecule during microsphere production with uniform distribution. Porous PLGA microspheres are also used to achieve much higher adsorption capacities of a short peptide than non‐porous microspheres of the same material.

D-2-3 光干渉断層計測法を用いた紙へのインク浸透過程の可視化

It is important to understand behavior of ink penetration into paper for designing inkjet process which enable both high speed and high quality of print. However, there was no method to visualize the phenomena directly. In this study, to visual ize ink penet ration, the de vice based on optical coherence to mography has bee n developed. Optical coherence tomography is the technology acquiring cross-sectional images of objects in non-destructive observation. Ink penetration process has been observed as the time-va rying cross-sectional images of paper through the use of this device. In addition, quantitative evaluation of penetration around ink and paper has become available as displacement of boundary surface of penetration in cross-sectional images.

An Inkjet-Printed Microfluidic RFID-Enabled Platform for Wireless Lab-on-Chip Applications

This paper introduces the first-of-its-kind wireless passive sensing platform combining radio frequency identification (RFID), microfluidics, and inkjet printing technology that enables remote fluid analysis and requires as little as 3 μL of fluid. The demonstrated variable microfluidic capacitors, resonators, and RFID tags are fabricated using a novel rapid, low-cost, and low-temperature additive inkjet process, making them disposable. However, even with their disposable nature, the RF microfluidic devices exhibit repeatability and long-term reusability for accurately detecting water, various alcohols, and % content of water/alcohol mixtures down to 1% water in ethanol. While the main discussion is on fluid sensing, the demonstrated components can also be used in fluid-tunable RF applications.

Inkjet-Printed In2O3 Thin-Film Transistor below 200 °C

High-performance In2O3 thin-film transistors could be prepared by an inkjet-printing method below 200 °C with a single precursor and solvent formulation. The self-combustion reaction took place with the electrical properties of In2O3 at a low temperature of 147 °C, which was confirmed by X-ray photoelectron spectroacopy and thermal analysis. The electrical properties after postannealing at 200 °C were as follows: a mobility of 3.98 cm(2)/V·s, a threshold voltage of 1.83 V, a subthreshold slope of 0.4 V/dec, and an on-to-off current ratio of 10(8), which are the best properties by an inkjet process thus far. The positive bias stability was much improved by postannealing, and good negative bias stability was obtained.

In/Ga-Free, Inkjet-Printed Charge Transfer Doping for Solution-Processed ZnO

An In/Ga-free doping method of zinc oxide (ZnO) is demonstrated utilizing a printable charge transfer doping layer (CTDL) based on (3-aminopropyl)triethoxysilane (APS) molecules. The self-assembled APS molecules placed on top of ZnO thin films lead to n-type doping of ZnO and filling shallow electron traps, due to the strong electron-donating characteristics of the amine group in APS molecules. The CTDL doping can tune the threshold voltage and the mobility of the ZnO thin-film transistors (TFTs) as one varies the grafting density of the APS molecules and the thickness of the underneath ZnO thin films. From an optimized condition, high-performance ZnO TFTs can be achieved that exhibit an electron mobility of 4.2 cm(2)/(V s), a threshold voltage of 10.5 V, and an on/off current ratio larger than 10(7). More importantly, the method is applicable to simple inkjet processes, which lead to produce high-performance depletion load ZnO inverters through selective deposition of CTDL on ZnO thin films.

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.

Comparison of Organic Pulse-Generator Circuits for Ferroelectric Memories Fabricated by All-Additive Printing

Printed organic thin-film transistor (OTFT) technology has the potential to enable ubiquitous, inexpensive, flexible electronic systems. Realization of this vision requires circuit design techniques sensitive to the constraints of the technology, as well as integration with components such as memory, sensors, and displays. The OTFT fabrication process is much less mature than silicon technologies, and direct implementation of conventional complementary designs is challenging due to the relatively low yield, high variability, and drift instability of printed OTFTs. Here we demonstrate an OTFT-specific approach to design with a pulse generator circuit for writing non-volatile thin-film ferroelectric (FE) memory. The approach takes into account the constraints of existing OTFT processes and can be extended to other circuits. The new circuit, and a more conventional complementary pulse-generator, are designed, fabricated, and tested in an additive ink-jet OTFT process.

Completely Etch-Free Fabrication of Multifilamentary Coated Conductor Using Inkjet Printing and Electrodeposition

Filamentization has been proven to be an effective way to reduce the ac loss of coated conductor superconducting tapes. However, all filamentization techniques to date involve material removal at some stage of processing. Utilizing inkjet printing and electrodeposition, a novel, completely etch-free method of fabricating multifilamentary RE-Ba-Cu-O (REBCO, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{RE} = \hbox{rare-earth}$</tex> </formula> ) superconducting tapes has been developed. Multiple insulating lines were fabricated on biaxially-textured MgO-buffered substrates by inkjet printing. Multifilamentary REBCO was obtained by preferential deposition of the superconductor between the insulating lines. Selective deposition of silver by electrodeposition on REBCO filaments was also achieved to create a multifilamentary conductor with a complete etch-free process. Due to the highly resistive barrier lines, reduced ac loss with minimized coupling was achieved in the multifilamentary REBCO tapes. Optimization of the inkjet and REBCO deposition process is underway to achieve a combination of high critical current and low ac losses by this completely etch-free technique.

Statistical Manufacturing Model of Printing Technology

There has been an evident increase in the demand for accurate and complex patterns for particles used in microsized electronic devices. Direct printing technology has been promoted as a solution for these needs, as the development of this technology provides both economical and environmental benefits, as well as being a time and energy saving process. Research in the field of printing technologies is still in the initial stages, involving the study of physical and chemical properties of printing materials. There are several methods currently using direct printing methods: microdispensing deposition write (MDDW), maskless mesoscale materials deposition (M3D), and inkjet printing. This study explores the direct printing methods of sequential and randomized printing associated with MDDW, M3D, and inkjet printing using computer simulations compared with actual experimentations. Sequential printing involves depositing particles onto the substrate in a specific order based on particle size. This method is associated with MDDW, where a relatively high viscous ink is dispensed onto the substrate so that particle sizes maintain an order in relation to one another, effectively producing a higher packing factor. Randomized printing involves the dispensing of various sizes of particles onto the substrate in a random order, as in inkjet printing. With this process, the probability of obtaining an efficient packing factor is unlikely and decreases even more with particle size. Therefore, the monolayer method, involving the deposition of individual particles, was developed to increase the packing factor when using the inkjet process. The results presented in this study proved that monolayering methods coincide with the projections predicted by the computer simulation. Sequential packing (MDDW) provides a shorter and higher range of packing factors than that of random packing sequences (ink jet); thus showing sequential packing to be the more efficient method. Sequential packing is closely related to the printing of high viscosity ink because of the higher packing factor that this method provides. An ink with increased viscosity allows for better conductivity which is essential in the development of improved nanoprinting technologies. This study provides evidence for the most efficient means of increasing the packing factor of particles; these methods offer the opportunity for technological advancement and commercialization of nanoprinting materials.

Study on Key Technology of Flatbed Inkjet Process and Equipment

Based on the flatbed inkjet printing technology development status at home and abroad, provided an overview of the flatbed inkjet device and technology principle, and introduced the required ink and plate. To focus on the flatbed inkjet device which the plate is fixed and the print head moves, put forward the mechanical design requirements. Besides, from the structure and layout of the device, elaborated the types of the flatbed inkjet device innovative ideas of design. Finally, summarized the advantages and disadvantages of the flatbed inkjet technology, and forecast its development prospects. To have some help in better understanding and application of flatbed inkjet technology.

Comparison of Static and Dynamic Printed Organic Shift Registers

Dynamic and static shift-register circuits are fabricated with an inkjet process for printing complementary organic semiconductors. The static design is based on edge-triggered master-slave flip-flops, and the dynamic design is based on a true-single-phase-clock architecture. The merits and drawbacks of the two approaches are considered and compared.

Study on Micron-Sized Colloidal Ink Formulations and Colloidal Patterns by Inkjet Printing

The feasibility of inkjet printing of colloidal dispersion inks to arrange colloids in desired locations was investigated with different ink formulations and inkjet process variables. In order to maintain the structural stability of colloidal patterns fabricated on the substrate from externally applied forces such as mechanical, chemical and thermal stimuli, thermally curable binder was formulated into the colloidal ink formulations. Circularly aggregated colloidal pattern uniformly covered with the binder coating was created using a piezoelectric inkjet on a polymer substrate, indicating that colloidal micro-patterning by inkjet printing could be an effective method to control geometry of colloidal patterning on substrates.

Multilayer Inkjet Printing of Millimeter-Wave Proximity-Fed Patch Arrays on Flexible Substrates

Flexible inkjet-printed proximity-fed patch antennas, designed for the 24-GHz Industrial, Scientific, and Medical (ISM) band, are demonstrated in this letter for the first time featuring a multilayer inkjet deposition process. Inkjet printing of antennas allows for the low-cost, noncontact, and additive fabrication of RF components onto nearly any host substrate or package. The inkjet-printing process exhibited in this leter is the first inkjet process to demonstrate multilayer printed antennas, enabled by a new printable dielectric ink that allows for the deposition of thick dielectric layers. Printed coupled patch antennas with realized gains of over 4 dBi and four-element coupled patch arrays with gains of over 7 dBi are demonstrated on a flexible liquid crystal polymer (LCP) substrate. The antenna gain, return loss, and pattern are presented and demonstrate the repeatability and design flexibility of the novel inkjet-deposition process.