Reverse Offset Printing Research Articles

Printing pressure optimization in reverse offset printing for micrograting fabrication

Among the various printing technologies available, reverse offset printing is the most promising for transferring fine patterns. This study reports the experimental results of interfacial adhesion and elastic deformation of a blanket during the printing process to demonstrate the fabrication of a high-resolution silver thin-film pattern. Additionally, a silicon wafer was used as the printing template, which allowed for the production of a high-resolution template more easily and at a lower cost than conventional glass templates. We successfully patterned line/space = 4 μm/4 μm using the proposed printing technique, and this resolution can be applied to X-ray diffraction gratings according to simulations.

Fully Printed Cellulose Nanofiber-Ag Nanoparticle Composite for High-Performance Humidity Sensor.

This paper reports a high-performance humidity sensor made using a novel cellulose nanofiber (CNF)-silver nanoparticle (AgNP) sensing material. The interdigital electrode pattern was printed via reverse-offset printing using Ag nano-ink, and the sensing layer on the printed interdigitated electrode (IDE) was formed by depositing the CNF-AgNP composite via inkjet printing. The structure and morphology of the CNF-AgNP layer are characterized using ultraviolet-visible spectroscopy, an X-ray diffractometer, field emission scanning electron microscopy, energy-dispersive X-ray analysis, and transmission electron microscopy. The humidity-sensing performance of the prepared sensors is evaluated by measuring the impedance changes under the relative humidity variation between 10 and 90% relative humidity. The CNF-AgNP sensor exhibited very sensitive and fast humidity-sensing responses compared to the CNF sensor. The electrode distance effect and the response and recovery times are investigated. The enhanced humidity-sensing performance is reflected in the increased conductivity of the Ag nanoparticles and the adsorption of free water molecules associated with the porous characteristics of the CNF layer. The CNF-AgNP composite enables the development of highly sensitive, fast-responding, reproducible, flexible, and inexpensive humidity sensors.

High-resolution printing of micrometer-scale copper electrode: From ink formulation and process optimization to application

In the rapidly advancing field of electronics, there is a growing demand for devices to be miniaturized with high-resolution patterns and compact, straightforward configurations, all while maintaining cost competitiveness. Precision patterning of conductive nano ink based on inexpensive metals offers an effective solution. This technique has proven compatibility with numerous integrated electronics. However, conventional patterning techniques face difficulties achieving high resolution, uniform thickness, and compatibility with environments prone to oxidation. Here, we optimize the reverse offset printing process and its ink formulation for green manufacturing of high-quality, high-resolution conductive micropatterns. The oleate ligand on the surface of Cu nanoparticles (CuNPs) is replaced by polyvinylpyrrolidone, which is more suitable for the steric stabilization of CuNPs in eco-friendly, polar solvent. Then, in consideration of the reverse offset printing mechanism, solvents and additives are evaluated to prepare a reverse offset printable ink. By examining the change in printability according to the composition and process parameters, we determine the printable composition range and process conditions. High-quality CuNP micropatterns with a fine line width of 10 μm, narrow spacing, sharp edge definition, and high uniformity are achieved. Finally, the reverse offset printed CuNP micropatterns are successfully implemented in thermistor microarrays as a potential application.

Arc-to-sheet printer for high-precision patterning with positional errors below 6 ppm at 3σ level: Trochoidal trajectory mechanism for rotary motion of arc

Pattern registration accuracy is a key property in printing processes, especially for miniaturized printed electronic devices that require the overlay of multiple layers. Except for inkjet and screen printing, various printing methods such as gravure offset, flexographic, and reverse offset printing typically use a roll-to-sheet type printer; however, registration has been limited, especially in the machine direction because of the speed variation in rotary motion of a cylindrical roll. We developed an arc-to-sheet type printer in which the rotary motion of an arc was realized by a trochoidal trajectory because such a mechanism can only be constructed using the translational motions of high-precision linear actuators. A prediction model for the behavior of the contact point of the arc during printing was also developed, along with a method for compensating for mechanical and assembly errors, which was verified by laser displacement measurements and torque exerted on the linear motor of table. Cu patterns reverse offset printed by the developed arc-to-sheet printer had positional errors of less than 3σ < 6 ppm with an optimized processing condition, achieving an unprecedented level of accuracy in printed electronics.

Oxide TFTs with S/D-contacts patterned by high-resolution reverse-offset printed resist layers

Besides the metal oxide thin film transistors (TFTs) in flat-panel displays that are fabricated using vacuum-processes, there is a growing interest in the fabrication of metal oxide TFTs by means of scalable, low-cost solution and printing processes for applications such as flexible displays and biosensors. Although devices with printed semiconductor and gate insulator can exhibit good electrical performance, source/drain-contacts (S/D) printed from silver (Ag) nanoparticles (NPs) typically suffer from deteriorated electrical characteristics and stability problems. On the other hand, metals providing good contacts, such as aluminum (Al), titanium (Ti) and molybdenum (Mo), cannot be formed as air-stable NPs. To overcome these issues, we have developed a patterning method based on high-resolution reverse-offset printing (ROP) of a sacrificial polymer resist layer. ROP delivers patterns with micrometer-level resolution and steep sidewalls, which are ideal for patterning vacuum-deposited metal contacts at high resolution via lift-off process. Solution-processed indium oxide (In2O3) TFTs were successfully fabricated by using ROP lift-off process for patterning of gate and S/D-electrodes using Al. The fabricated In2O3-based TFTs with Al S/D-contacts exhibit good uniformity, constant mobility (μ sat) ∼ 2 cm2 (V s)−1 over a wide range of width/length-ratios (W/L) and almost zero turn-on voltage (V on) ∼ −0.2 V. TFTs down to 5 µm channel lengths were successfully patterned. Further development of the fabrication process could lead to flexible fully-print-patterned high-resolution TFT backplanes for flexible displays, biosensors, photosensors and x-ray detectors.

High-Quality Microprintable and Stretchable Conductors for High-Performance 5G Wireless Communication.

With the advent of 5G wireless and Internet of Things technologies, flexible and stretchable printed circuit boards (PCBs) should be designed to address all the specifications necessary to receive signal transmissions, maintaining the signal integrity, and providing electrical connections. Here, we propose a silver nanoparticle (AgNP)/silver nanowire (AgNW) hybrid conductor and high-quality microprinting technology for fabricating flexible and stretchable PCBs in high-performance 5G wireless communication. A simple and low-cost reverse offset printing technique using a commercial adhesive hand-roller was adapted to ensure high-resolution and excellent pattern quality. The AgNP/AgNW micropatterns were fabricated in various line widths, from 5 μm to 5 mm. They exhibited excellent pattern qualities, such as fine line spacing, clear edge definition and outstanding pattern uniformity. After annealing via intense pulsed light irradiation, they showed outstanding electrical resistivity (15.7 μΩ cm). Moreover, they could withstand stretching up to a strain of 90% with a small change in resistance. As a demonstration of their practical application, the AgNP/AgNW micropatterns were used to fabricate 5G communication antennas that exhibited excellent wireless signal processing at operating frequencies in the C-band (4-8 GHz). Finally, a wearable sensor fabricated with these AgNP/AgNW micropatterns could successfully detected fine finger movements in real time with excellent sensitivity.

High-resolution patterning of silica nanoparticle-based ionogels by reverse-offset printing and its characterization

In this study, nanoparticle-based, high-resolution patternable ionogels are presented to provide a route for realizing printed solid-state ionic devices. By incorporating an ionic liquid (IL) into a spherical silica nanoparticle suspension, a quasi-solid ionogel layer compatible with reverse-offset printing (ROP) with a spatial resolution of approximately 5 μm was realized. In situ near-infrared (NIR) spectroscopic analysis revealed the drying kinetics of the ionogel ink during printing, and a temporal margin for successful patterning in relation to its dry state was provided. In contrast to polymer-based gels, the present ionogel can be regarded as a porous medium of silica filled with ionic liquids with a certain degree of saturation. By optimizing the ink formulations, ROP patterning was successful for saturation up to 102%, indicating the nanoscale pores between silica nanoparticles can be fully used as an ion-conductive phase in the proposed patternable gel. The conductivity depends drastically on saturation, with a saturation exponent of approximately −7 according to Archie’s law. From a complementary scratch test, an ionogel at a saturated condition still exhibited fragile but solid-like characteristics. As a demonstration, planar micro-supercapacitors fully printed with reverse-offset printable ionogel and carbon inks were fabricated. A comparison with a drop-casted IL showing a similar capacitance indicates a limited ability of the carbon nanoparticle material used here, while a relatively high resistance of the silica-nanoparticle-based ionogel hinders a fast cyclic voltammetry response.

Actively compensated precision overlay in a reverse-offset printing system for realizing printed electronics of a large-area and multi-layer structure

This study focuses on developing a way to improve the overlay accuracy of the reverse-offset printing system. Investigations were made into how the overlay error is distorted by the six-DOF position error of the roller during the rolling contact through literature review and finite element (FE) simulations. This means that controlling the motion error actively in MD, CD, and yaw direction between the offset roller and the substrate (or cliché) can be the control knobs to compensate for the overlay errors caused by the six-DOF motion errors during rolling contact. With these control knobs, a novel active and automatic correction algorithm of overlay error for a reverse-offset printing system is proposed. A novel reverse-offset printing system is developed to precisely control the six-DOF motion of the roller and print the patterns with high position repeatability. The core modules for the proposed overlay compensation are also explained. To evaluate the proposed overlay compensation algorithm, an overlay printing test is performed in the developed printing system. With the proposed correction algorithm, the overlay error is converged to 1.9 μm and 2.4 μm in CD and MD, respectively.

Development of a Novel Reverse Offset Printer Equipped with Double-Layer Blanket (DLB) for Micropattern Printing on 3D Curved Surfaces

The double-layer blanket (DLB) reverse offset is a newly designed printing process for patterning electronic circuits on a 3D curved surface. Unlike the existing reverse offset process, the DLB reverse offset utilizes an offset roll composed of two layers comprising polydimethylsiloxane (PDMS) and a thick, soft cushioned rubber to print microelectrode patterns and transparent electrodes on a curved surface. The optimal printing process was determined by adjusting the printing pressure and printing speed for horizontal and vertical micropatterns, based on which transparent electrodes with metal mesh and honeycomb structures with a line width of 30 μm and pitch of 600 μm with micropatterns ranging from 30 μm to 60 μm were printed on a curved surface. Ag ink was used, and the 3D curved surface indicated a print quality similar to that of the flat surface for both the vertical and horizontal patterns and transparent electrodes. The DLB reverse offset technique demonstrated the possibility of printing on a 3D curved surface and is expected to broaden the range of printed electronics to applications such as smart glasses and 3D shape sensors.

Nickel oxide-based flexible thin-film NTC thermistors by using reverse offset printing

In recent years, the use of printing methods to fabricate electronic devices (printed electronics) has attracted attention because of their low cost and low environmental impact. Printing technology enables the high-throughput fabrication of electrical circuits on film substrates, thereby providing inexpensive personal healthcare devices to monitor health status in real-time, for example. Temperature detection is one of the central concerns as a fundamental physical quantity in various fields. In 2013, a highly sensitive flexible thermistor was reported by formulating aqueous inks of nickel oxide (NiO) nanoparticles for inkjet printing. However, it required a high-temperature calcination process of more than 200 °C, which led to the use of expensive polyimide films with high heat resistance. It is necessary to promote further the development of low-temperature processes for printed thermistors to realize flexible negative temperature coefficient (NTC) thermistors at low cost using printed electronics technology. Moreover, in screen printing and inkjet printing, the definition of the ink pattern applied on the substrate changes due to spreading and coffee distortion phenomena, and the thickness between sensors becomes non-uniform, which is a structural consistency problem that can lead to variations in sensing performance. Therefore, in this study we developed low-temperature processable printed NTC thermistors with a temperature-sensitive layer of NiO by using reverse offset printing. The NTC thermistors were fabricated by printing a comb-like pattern of silver nanoparticles and a thin NiO film. In addition, the low-temperature formation of a NiO layer by oxygen plasma treatment was investigated, and x-ray photoelectron spectroscopy was used to carry out compositional analysis of the surface. Together with the plasma-assisted calcination, a flexible NTC thermistor formed on polyethylene terephthalate film is demonstrated.

Simple, Fast, and Scalable Reverse-Offset Printing of Micropatterned Copper Nanowire Electrodes with Sub-10 μm Resolution.

Copper nanowires (CuNWs) possess key characteristics for realizing flexible transparent electronics. High-quality CuNW micropatterns with high resolution and uniform thickness are required to realize integrated transparent electronic devices. However, patterning high-aspect-ratio CuNWs is challenging because of their long length, exceeding the target pattern dimension. This work reports a novel reverse-offset printing technology that enables the sub-10 μm high-resolution micropatterning of CuNW transparent conducting electrodes (TCEs). The CuNW ink for reverse-offset printing was formulated to control viscoelasticity, cohesive force, and adhesion by adjusting the ligands, solvents, surface energy modifiers, and leveling additives. An inexpensive commercial adhesive handroller achieved a simple, fast, and scalable micropatterning of CuNW TCEs. Easy production of high-quality CuNW micropatterns with various curvatures and shapes was possible, regardless of the printing direction. The reverse-offset-printed CuNW micropatterns exhibited a minimum of 7 μm line width and excellent pattern qualities such as fine line spacing, sharp edge definition, and outstanding pattern uniformity. In addition, they exhibited excellent sheet resistance, high optical transparency, outstanding mechanical durability, and long-term stability. Flexible light-emitting diode (LED) circuits, transparent heaters, and organic LEDs (OLEDs) can be fabricated using high-resolution reverse-offset-printed CuNW micropatterns for applications in flexible transparent electronic devices.

Reverse-Offset Printing of Polymer Resist Ink for Micrometer-Level Patterning of Metal and Metal-Oxide Layers.

Printed electronics has advanced during the recent decades in applications such as organic photovoltaic cells and biosensors. However, the main limiting factors preventing the more widespread use of printing in flexible electronics manufacturing are (i) the poor attainable linewidths via conventional printing methods (≫10 μm), (ii) the limited availability of printable materials (e.g., low work function metals), and (iii) the inferior performance of many printed materials when compared to vacuum-processed materials (e.g., printed vs sputtered ITO). Here, we report a printing-based, low-temperature, low-cost, and scalable patterning method that can be used to fabricate high-resolution, high-performance patterned layers with linewidths down to ∼1 μm from various materials. The method is based on sequential steps of reverse-offset printing (ROP) of a sacrificial polymer resist, vacuum deposition, and lift-off. The sharp vertical sidewalls of the ROP resist layer allow the patterning of evaporated metals (Al) and dielectrics (SiO) as well as sputtered conductive oxides (ITO), where the list is expandable also to other vacuum-deposited materials. The resulting patterned layers have sharp sidewalls, low line-edge roughness, and uniform thickness and are free from imperfections such as edge ears occurring with other printed lift-off methods. The applicability of the method is demonstrated with highly conductive Al (∼5 × 10–8 Ωm resistivity) utilized as transparent metal mesh conductors with ∼35 Ω□ at 85% transparent area percentage and source/drain electrodes for solution-processed metal-oxide (In2O3) thin-film transistors with ∼1 cm2/(Vs) mobility. Moreover, the method is expected to be compatible with other printing methods and applicable in other flexible electronics applications, such as biosensors, resistive random access memories, touch screens, displays, photonics, and metamaterials, where the selection of current printable materials falls short.

Tunable Reverse Offset Printing with a Stretchable Blanket for Fabricating Flexible Printed Electronics

The cover page shows the illustration of controlled pattern shrinkage in reverse offset printing. Young Tae Cho and co-workers demonstrate in their article, number 2001537, that the pattern size reduction by a flexible blanket material with simple mechanical stretching and releasing shed light on the low-cost, scalable, and high-resolution printing for printed electronics.

Embedded Reverse-Offset Printing of Silver Nanowires and Its Application to Double-Stacked Transparent Electrodes with Microscale Patterns.

We propose an embedded reverse-offset printing (EROP) method, which generates silver nanowire (AgNW) transparent electrodes for display applications. The proposed EROP method can solve the two critical issues of microscale pattern formation and surface planarization. The AgNW electrode had a transmittance of 82% at 550 nm, a sheet resistance of 12.2 Ω/sq, and a 3.27 nm smooth surface. We realized the roll-based pattern formation of AgNW on a plastic substrate as small as 10 μm with negligible step differences to facilitate the proposed method. The proposed EROP method also produced a double-stacked AgNW electrode, enabling the simultaneous operation of separately micropatterned devices. To verify the usefulness of EROP, we fabricated an organic light-emitting diode (OLED) device to demonstrate leakage current reduction and efficiency improvement compared with a conventional indium tin oxide (ITO)-based OLED device. The EROP-based OLED showed 38 and 25% higher current efficiencies than an insulator-patterned AgNW OLED and a conventional ITO-based OLED, respectively.

A Study on the Selection of Highly Flexible Blanket for Reverse Offset Printing

A Study on the Selection of Highly Flexible Blanket for Reverse Offset Printing

Facile and Low Cost Temperature Compensated Humidity Sensor and Signal Conditioning System

Most relative humidity sensors are resistive or capacitive sensors. It’s a fact that the resistance and capacitance of a vast majority of such sensors also depend on the surrounding temperature and a change of temperature can cause significant errors in the final reading of relative humidity. This fact of temperature dependence is scarcely investigated in development of humidity sensors. In this work, a very simple temperature compensation method has been developed that automatically eliminates the effect of change in temperature from the final output without requiring separate measurement of temperature or any data processing. Amorphous polyethylene oxide (PEO) was used as the active material for humidity sensor owing to its high sensitivity and almost linear response. Interdigitated type sensor electrodes (IDE) were fabricated using reverse offset printing on glass substrate and the active layer was deposited through spin coating. An identical twin sensor was fabricated with the same parameters and was additionally encapsulated form the open environment. The dummy sensor was used as opposing pair with the active sensor in a bridge configuration to achieve temperature compensation. The bridge sensitivity was recorded to be ~2.9 mV/%RH that was further improved to 100 mV/%RH using a differential instrumentation amplifier based signal conditioning circuit. The sensor system was deployed in a real-life relative humidity measurement with changing temperature that returned a remarkable accuracy of 98.76%. The error due to temperature dependence reduced from 22.4% to just 1.24%. The transient response time of the sensor was found to be ~2.4 s.

Tunable Reverse Offset Printing with a Stretchable Blanket for Fabricating Flexible Printed Electronics

Reverse offset printing (ROP) is receiving increasing attention as an emerging technology for printed electronics due to its rapid, environment‐friendly fabrication processes. A tunable ROP process is proposed by exploiting the controlled elastic deformation of a stretchable blanket. First, the flat elastomeric blanket is elastically stretched before coating with the printing ink. Next, Ag ink is coated on the surface of a supporting substrate and sequentially transferred to a prestrained elastomeric blanket. Second, the patterned cliché is rolled over the prestrained blanket surface by applying an optimized pressure for patterning. Finally, releasing the strain in the patterned elastomeric blanket leads to a pattern deformation on pitch and sizes. A decrease in the line width and pitch is demonstrated using a tunable ROP process with a stretchable blanket. This unique tunable printing process offers the capability of low‐cost fabrication of various microstructures from a single cliché using simple mechanical stretching and releasing.

Taking the accuracy of printed electronics beyond 1μm

Researchers at VTT Technical Research Centre of Finland are developing printed electronics beyond the 1μm mark. Reverse-offset printing technique can achieve sub-micron line resolution and μm-scale alignment accuracy

Decomposition of pattern distortions by the Spread polynomial model in roll-to-sheet reverse offset printing

The repeatability of manufacturing process is one of the prerequisite aspects in printed electronics. Particularly, the requirement for the positioning accuracy becomes severe as the miniaturization of printed traces develops, patterning area enlarges, and potential applications widen. Therefore, a measure to quantify the effect of various processing parameters on the global registration error of printed patterns is highly important. In this study, the effect of typical processing parameters appeared in a roll-to-sheet, high-resolution printing (reverse offset printing) including synchronization mismatch, tilting of the roll, unevenness of substrate, were systematically investigated. A fitting model on the basis of Spread polynomials successfully decomposed complicated geometrical distortions into basic components such as scale, skew, rotation, trapezoid, and quadratic warping. The relationship between geometrical distortions and processing parameters was summarized.

Newly developed soft blanket reverse-offset (SBR) printing technology for forming widely patterned layers on curved surfaces

We have been employing novel printing technologies in three-dimensional printed electronics applications, to form electronic devices on curved or three-dimensional object surfaces. In this paper, we report on a newly developed printing technology named ‘soft blanket reverse-offset’ (SBR) printing, which was developed to create wide and flat patterned layers with uniform thicknesses on curved surfaces. SBR printing is an extension of conventional reverse-offset printing and uses an extremely thick and soft blanket (referred to as a “soft blanket”) as an offset roller. We also created a new thick stencil printing plate and a two-layered soft blanket construction that avoids the formation of contact-defects. In addition, we have also succeeded in printing wide and flat patterned layers onto curved surfaces using commercially available silver nanoparticle inks. The printed layers are also characterized by uniform thicknesses and low resistivities, equivalent to those of layers printed on planar substrates.