Ink Patterns Research Articles

A highly reliable copper nanowire/nanoparticle ink pattern with high conductivity on flexible substrate prepared via a flash light-sintering technique.

In this work, copper nanowires (NWs) and Cu nanoparticles (NPs) were employed to increase the reliability of a printed electrode pattern under mechanical bending fatigue. The fabricated Cu NW/NP inks with different weight fractions of Cu NWs were printed on a polyimide substrate and flash light-sintered within a few milliseconds at room temperature under ambient conditions. Then, 1000 cycles of outer and inner bending fatigue tests were performed using a lab-made fatigue tester. The flash light-sintered Cu NW/NP ink film with 5 wt % Cu NWs prepared under the flash light-sintering conditions (12.5 J·cm–2 irradiation energy, 10 ms pulse duration, and one pulse) showed a lower resistivity (22.77 μΩ·cm) than those of the only Cu NPs and Cu NWs ink (94.01 μΩ·cm and 104.15 μΩ·cm, respectively). In addition, the resistance change (ΔR·R0(–1)) of the 5 wt % Cu NWs Cu NW/NP film was greatly enhanced to 4.19 compared to the 92.75 of the Cu NPs film obtained under mechanical fatigue conditions over 1000 cycles and an outer bending radius of 7 mm. These results were obtained by the densification and enhanced mechanical flexibility of flash light-sintered Cu NW/NP network, which resulted in prevention of crack initiation and propagation. To characterize the Cu NW/NP ink film, X-ray diffraction and scanning electron microscopy were used.

A Low-Cost Hyperspectral Scanner for Security Printing

We demonstrate a hand-held scanner that acquires two-dimensional images with up to 40 distinct wavelength channels. Light is collected through a combined slit and illumination assembly, dispersed by a diffraction grating film and analyzed using a webcam. Custom software is used to track the scanner motion and build the hyperspectral image data in real time. We tested the performance on printed fluorescent ink patterns that are of interest for security printing applications, and obtained results that are consistent with spectra acquired using a laboratory-grade spectrofluorometer.

Screen-pad printing for electrode patterning on curvy surfaces

Pad printing is a simple but effective method for fabricating electrodes onto complex curved surfaces. In this method, ink is picked up from the gravure plate by the soft pad, after which the ink pattern is transcriptionally formed from the pad to the final substrate. However, this printing method has some problems; primarily, it is difficult to form thick and large patterns. To address these limitations, we developed a new printing technique called "screen-pad printing." In this technique, ink is first screen-printed onto a blanket made of silicone resin, after which the ink pattern is picked up by the soft pad, and the pattern on the pad is transferred to the substrate. In this paper, we describe the features of the developed screen-pad printing technique when forming patterns on objects that have complex surfaces. Further, the impact of our new method is analyzed by comparing the experimental results of screen-pad printing with results obtained from conventional pad printing.

Microcontact printing large-area pattern of catalytic Pd ink with a polyelectrolyte modified stamp for selective electroless deposition of nickel on glass substrate

In this paper, a simple and effective method to fabricate a large-area conductive metal pattern on glass substrate is described. This method involves microcontact printing (μCP)of a thermo-sensitive St-co-NIPAAm/Pd nanoparticle-based ink on a glass substrate to create the catalytic site, onto which nickel is subsequently deposited by an electroless plating method, to obtain the desired metal pattern. The Pd nanoparticles reduced and stabilized by styrene-N-isopropylacrylamide co-oligomer showed their well dispersion in the water without surfactant and reductant in the mixture and these nanoparticles adhered well to glass surface. Through a carefully examine the effect of surface modification of rubber stamp using either cationic or anionic polyelectrolyte on the surface properties of rubber and resolution of CP, our results indicates that a complete and uniform Ni pattern can be produced simply by modifying the pristine stamp surface with a positively charged polyelectrolyte (poly(diallyldimethylammonium chloride), PDDA). It enhances the affinity between Pd ink and the PDDA-modified stamp and produces a uniform ink layer on the substrate. The excellent adhesion of the deposited NiP coating to the substrate was ascertained by the scotch tape test method.

Screen-offset printing for fine conductive patterns

Screen printing is a useful method for fabricating electrodes or signal wires of electronic devices. However, finer patterns, e.g., 50-μm-wide, are difficult to form. Herein, we introduce a newly developed printing technique called “screen-offset printing,” as a candidate method for solving this problem. In this process, first, ink patterns are screen-printed on a silicone-resin blanket; they are then transferred from the blanket to an object. In the present study, we analyze the features of screen-offset printing by observing printed conductive patterns, and elucidate the impact of this method by comparing the experimental results of screen-offset printing and conventional screen printing. In addition, we demonstrate the fabrication of fine patterns with a line and space (L/S) of 50/50 and 30/30μm.

Fabrication of copper wiring by micro-contact printing method and electroless plating and electroplating

A micro-contact printing (µCP) method has been applied to the fabrication of microstructures and electronics. We have successfully fabricated a copper wiring structure on flexible substrates using a combination of µCP, electroless plating, and electroplating. A nucleating agent ink pattern was printed by µCP onto polyethylene terephthalate, and polyethylene naphthalate. Nickel and copper thin films were electrolessly plated onto the pattern, and used as a conductive layer for subsequent copper electroplating. Copper wiring structures with a half-pitch of a 100 µm and a 250 µm line-and-space pattern, were successfully produced on flexible films at temperatures below 100 °C.

Optimization of Reverse Offset Roll to Plate (RO-R2P) Through Contact Angle

The application of 5 μm nano-metal ink pattern has taken center stage for the field of cellular phones, organic solar cell, and so on due to its invisible property and high electrical conductivity. While the non-contact printing, such as ink jet and silk screen printing method, cannot print less than 40 um width pattern, reverse offset printing can control the accuracy of pattern width up to maximum 5 μm. However, due to its direct printing, fracture of final substrate is the biggest problem at the high pressure in the process. Therefore, the following rapid prototyping focuses on optimization of reverse offset printing based on low pressure and optimizing the contact angle as the primary parameters in achieving a high-resolution, 5 μm pattern. This paper proposes the sequence of contact angle (θ) based on the reverse offset printing process as: θ (Stage 1) > θ (Roll) > θ (Stage 2), θ (Stage 3). Through the experiment, a contact angle differential should be 5.4°≤ ∆θ ≤6.4° between roll and Stage 1, ∆θ≤10.1°, between roll and Stage 2, and ∆θ ≤ 13.4° between roll and Stage 3. Whereas the final pattern is not printed or non-continuous when the differential of contact is out of the proposed range, continuous high resolution of 5 μm pattern could be printed when the contact angle range and sequence are optimized as proposed method. Finally, the continuous and high resolution of 5 μm pattern is printed on the Kapton PV9101 when M1 is used for material of roll. Therefore, the continuous high resolution of 5 μm pattern could be produced by optimizing the range of contact angle in the reverse offset system. KeywordsContact Angle; Reverse Offset; Roll to Plate

Direct selective growth of ZnO nanowire arrays from inkjet-printed zinc acetate precursor on a heated substrate

Inkjet printing of functional materials has drawn tremendous interest as an alternative to the conventional photolithography-based microelectronics fabrication process development. We introduce direct selective nanowire array growth by inkjet printing of Zn acetate precursor ink patterning and subsequent hydrothermal ZnO local growth without nozzle clogging problem which frequently happens in nanoparticle inkjet printing. The proposed process can directly grow ZnO nanowires in any arbitrary patterned shape, and it is basically very fast, low cost, environmentally benign, and low temperature. Therefore, Zn acetate precursor inkjet printing-based direct nanowire local growth is expected to give extremely high flexibility in nanomaterial patterning for high-performance electronics fabrication especially at the development stage. As a proof of concept of the proposed method, ZnO nanowire network-based field effect transistors and ultraviolet photo-detectors were demonstrated by direct patterned grown ZnO nanowires as active layer.

은 잉크를 이용한 그라비아 오프셋의 전극인쇄에서 닥터링 공정의 영향

In this paper, we analyzed the effects of doctoring process on the patterns of Ag ink in gravure off-set printing. The parameters of doctoring process were the angle and the pressure, which was represented by the depth of blade movement to the gravure roll, of doctor blade to the surface of gravure roll, and the angle of patterns engraved on the gravure roll to the doctor blade moving direction. The proper parameters were extracted for the fine patterns and they were 15 mm for the pressure, <TEX>$60^{\circ}$</TEX> for the blade angle. And the angle of patterns with respect to the blade movement should be less than <TEX>$40^{\circ}$</TEX> for the best results. The gravure off-set printing with the above parameters was carried out to print gate electrodes and scan bus lines of OTFT-backplane for e-paper. The line width of <TEX>$50{\mu}m$</TEX> was successfully obtained. The thickness of electrodes was <TEX>$2.5{\mu}m$</TEX> and the surface roughness was <TEX>$0.65{\mu}m$</TEX> and the sheet resistance was <TEX>$15.8{\Omega}/{\Box}$</TEX>.

A numerical study of the ink transfer process for roll-to-roll printing applications

An ink transfer process from the printing roll to the moving web was investigated using a computational fluid dynamics technique for the roll-to-roll application in the area of printed electronics. Emphasis was made on the shape of the transferred ink pattern in a realistic configuration. The shear-thinning effect of the conductive ink was treated using a generalized non-Newtonian fluid model. That is, the coefficients of the Carreau model were determined using the fluid dynamic property information of the commercially available conductive ink used in the roll-to-roll process. Also, the web handling speed was matched with that of the typical roll-to-roll process applied in printed electronics. Computational results show that the spatial variation of the shear rate is quite significant in the present configuration; therefore, the Carreau model better predicts the shape of the measurement data than Newtonian fluid in the range of the line thickness of 100–500 µm. It is also noted that the non-uniformity of the transferred ink that is experimentally observed is better predicted by the non-Newtonian model. It is conjectured that the distortion of the shape and the non-uniform distribution of the transferred ink are the prime sources for deterioration in printing quality. However, the fact that web handling speeds of up to 30 mpm (=0.5 m/s) do not significantly aggravate the degree of distortion still supports the main advantage of a cost-effective, continuously running roll-to-roll process in this speed range.

Influence of surface chemistry on inkjet printed carbon nanotube films

Carbon nanotube ink chemistry and the proper formulation are crucial for direct-write printing of nanotubes. Moreover, the correct surface chemistry of the self-assembled monolayers that assist the direct deposition of carbon nanotubes onto the substrate is equally important to preserve orientation of the printed carbon nanotubes. We report that the successful formulation of two single walled carbon nanotube (SWNT) inks yields a consistent, homogenous printing pattern possessing the requisite viscosities needed for flow through the microcapillary nozzles of the inkjet printer with fairly modest drying times. The addition of an aqueous sodium silicate allows for a reliable method for forming a uniform carbon nanotube network deposited directly onto unfunctionalized surfaces such as glass or quartz via inkjet deposition. Furthermore, this sodium silicate ingredient helps preserve applied orientation to the printed SWNT solution. Sheet resistivity of this carbon nanotube ink formula printed on quartz decreases as a function of passes and is independent of the substrate. SWNTs were successfully patterned on Au. This amine-based surface chemistry dramatically helps improve the isolation stabilization of the printed SWNTs as seen in the atomic force microscopy (AFM) image. Lastly, using our optimized SWNT ink formula and waveform parameters in the Fuji materials printer, we are able to directly write/print SWNTs into 2D patterns. Dried ink pattern expose and help orient roped carbon nanotubes that are suspended in ordered arrays across the cracks.

Pulsed-laser printing of silver nanoparticles ink: control of morphological properties

Fine electrically-conductive patterns of silver nanoparticles ink have been laser printed using the laser-induced forward transfer (LIFT) technique. LIFT is a technique that offers the possibility of printing patterns with high spatial resolution from a wide range of materials in solid or liquid state. Influence of drying the ink film, previous to its transfer, on the printed droplet morphology is discussed. The laser pulse energy and donor-receiver substrate separation were systematically varied and their effects on the transferred droplets were analyzed. The use of an intermediate titanium dynamic release layer was also investigated and demonstrated the possibility of a better control of both the size and shape of the printed patterns. Conditions have been determined for printing flat-top droplets with sharp edges. 21 µm width silver lines with 80 nm thickness have been printed with a smooth convex profile. Electrical resistivities of the transferred patterns are only 5 times higher than the bulk silver.

Excimer lasers drive large-area microprocessing

Excimer lasers emitting in the UV to far UV region are by nature the laser sources enabling the highest optical resolution and strongest material–photon interaction. At the same time, excimer lasers deliver unmatched UV pulse energies and output powers up to the kilowatt range. Thus, they are the key to fast and effective large area processing of smallest structures with micron precision. As a consequence, excimer lasers are the UV technology of choice when it comes to high-performance microstructuring with unsurpassed quality and process repeatability in applications such as drilling advanced ink jet nozzles or patterning biomedical sensor structures.

P‐90: A Tunable Whitepoint Hardware Solution for Monochrome Medical Displays

AbstractIn medical imaging, monochrome displays are offered with a bluebase or clearbase whitepoint. In this paper, a hardware solution using a foil with an ink pattern is presented that allows altering the whitepoint of a CCFL backlit LCD display between clearbase and bluebase, without the need to alter the lamps.

나노물질의 선택적 레이저소결을 이용한 유연전기소자 구현 연구현황

대부분의 유연전기소자는 플라스틱, 옷감, 종이와 같이 고온에 민감한 물질이기 때문에 열에 민감한 기판 위에 금속을 증착하고 패터닝할 수 있는 저온 공정의 개발이 필요하다. 최근 기존의 광식각과 진공증착 방법을 이용하지 않고 액상으로 금속 나노입자의 박막을 형성하고 선택적 레이저 소결을 이용하여 플라스틱에 열적손상을 최소화하고 고해상도의 금속 패터닝을 방법이 많은 연구가 활발히 진행되고 있다. 본 논문에서는 본 연구실에서 활발히 수행중인 나노물질의 선택적 레이저소결법을 이용하여 유연 디스플레이와 유연태양전지와 같은 유연전기소자의 개발 동향에 대해 알아보고 앞으로의 발전방향에 대해 논의한다.

Environmental protection of inkjet-printed Ag conductors

Electrically conductive silver nanoparticle ink patterns were fabricated using the inkjet printing method. Two different polymer films were used as the substrate materials. The patterns were exposed to humidity and salt fog and the electrical performance (sheet resistance and RF performance) as well as mechanical endurance (adhesion) were measured before and after the environmental tests. The electrical properties of the printed structures remained good in all the measurable samples. The adhesion between the ink and a substrate material appeared to be a greater challenge in harsh environments. Protection capabilities of one dip coated and one hot laminated barrier materials were evaluated during the environmental tests. The results showed that there is a need for environmental protection in printed electronics. Especially the laminated barrier films can offer a potential solution for shielding printed electronics in harsh environments as they can provide good mechanical protection, and can easily be integrated in roll-to-roll process.

Sintering condition effect on the characteristics of ink-jet printed silver pattern on flexible cellulose paper

This paper reports sintering condition effect on an ink-jet printed conductive pattern of silver ink made on a cellulose paper. To fabricate the conductive pattern on the cellulose paper, silver ink is ink-jet printed and the influence of sintering temperature and time is investigated in terms of electrical resistivity and morphology by using scanning electron microscope and atomic force microscope. Two-level baking process composed of soft baking and hard baking is found to be effective for silver nanoparticle network. The sintering temperature and time are strongly associated with the conductivity of the ink-jet printed pattern.

Directional Mobility and Adhesion of Water Drops on Patterned Superhydrophobic Surfaces

Directional mobility and controlled adhesion of water drops were obtained on superhydrophobic paper surfaces by generating high surface energy ink patterns using commercial desktop printing. By changing the curvature/shapes of the ink patterns, geometrical constraints were imposed on the movement of the three-phase liquid/solid/vapor contact line. With proper design of pattern shapes, the critical sliding angle of water drops was manipulated with respect to different directions. Adhesion tunability of water drops on superhydrophobic paper was established by design of chemical heterogeneity. Printing of 'checker' ink patterns with appropriate area fraction and feature dimensions allowed variation in the critical sliding angle of water drops. The manipulation of directional mobility and adhesion of water drops on superhydrophobic paper surfaces allows the design of novel components such as 2D flow paths, gates/diodes, junctions and drop size filters for emerging 2D paper-based microfluidics technology for biomedical diagnostic applications.

Patterns of Ink in Water and Air: Creating Radial Spreads of Ink in Water

Radial spreads are made by placing different types of ink and paint over each other. Then, when gravity 'activates' the spread, causing the ink to move outward, the resulting patterns of ink are photographed. Recent work shows how different types of ink react to the force of the spread (by, for instance, forming thin films, or becoming filamentous). Different types of ink can be used in conjunction to reveal different parts of the spread. Regular shapes in tessellations, underwater 3D forms, and airborne radial spreads have been observed. Radial spreads of ink in water can be seen in terms of both art and science. Artistic aspects include an exploration of ink textures, and comparisons are made with other natural and man-made materials. Parallels between radial spreads and organic life forms are made, and new juxtapositions of the 'birth, life and death' of the spreads are found. Connections are made between the small-scale world of ink in water, and large-scale objects, e.g. cosmic phenomena. Ambiguous imagery, requiring an imaginative contribution from the viewer, is explored. Long-term aims are to collaborate with those interested in the science of diffusion to build up visual profiles of inks, and also to develop 3D chromatography. Artistically, links with other natural forms will be explored. More images are at www.chronoscapes.co.uk.

The characterization of electrically conductive silver ink patterns on flexible substrates

Electrically conductive silver ink patterns were produced by the screen printing method. Paper, fabrics and plastics were used as the substrate materials. The electrical properties of the samples were characterized by sheet resistance measurement as a function of curing temperature and curing time. The mechanical properties of the samples were characterized by cross hatch adhesion test, bending test and tensile test. Depending on the process parameters and materials, the sheet resistance of the printed conductive patterns varied between 0.04 Ω/□ and 0.13 Ω/□. The curing temperature appeared to have a significant effect on the sheet resistance. In all cases sheet resistance decreased as a function of curing temperature. Adhesion between the substrates and the conductive patterns appeared to be good. The result of the bending test indicated that the resistivity of the silver ink patterns increased as a function of the bending cycle process. The results of the tensile and electrical tests showed that with the screen printing method it is possible to produce highly stretchable electrically conductive patterns for practical applications.