Formation of low surface energy separators with undercut structures via a full-solution process and its application in inkjet printed matrix of polymer light-emitting diodes

In this paper, low surface energy separators with undercut structures were fabricated through a full-solution process. These low surface energy separators are more suitable for application in inkjet printed passive-matrix displays of polymer light-emitting diodes. A patterned PS film was formed on the P4VP/photoresist film by microtransfer printing firstly. Patterned Au-coated Ni film was formed on the uncovered P4VP/photoresist film by electroless deposition. This metal film was used as mask to pattern the photoresist layer and form undercut structures with the patterned photoresist layer. The surface energy of the metal film also decreased dramatically from 84.6 mJ/m² to 21.1 mJ/m² by modification of fluorinated mercaptan self-assemble monolayer on Au surface. The low surface energy separators were used to confine the flow of inkjet printed PFO solution and improve the patterning resolution of inkjet printing successfully. Separated PFO stripes, complement with the pattern of the separators, formed through inkjet printing. The separators also realized the patterning of cathodes. A passive-matrix display device was obtained through the assistant patterning of low surface energy separators.     

Printing Methods and Materials for Large-Area Electronic Devices

Two digital printing methods for the fabrication of active matrix thin-film transistor (AM-TFT) backplanes for displays are described. A process using printed resists layers, referred to as digital lithography, was used to fabricate arrays of hydrogenated amorphous silicon TFTs. TFTs were also fabricated using a combination of digital lithography to pattern metals and inkjet printing to pattern and deposit a polymeric semiconducting layer. The relative performance of amorphous silicon and polymer TFTs were evaluated. The utility of digital lithographic processing was demonstrated by the fabrication of prototype reflective displays using electrophoretic media.     

Fully solution-processed organic thin-film transistors by consecutive roll-to-roll gravure printing

A high-performance/flexible organic thin-film transistor (OTFT) is fabricated by using all-step solution processes, which are composed of roll-to-roll gravure, plate-to-roll gravure and inkjet printing with the least process number of 5. Roll-to-roll gravure printing is used to pattern source/drain electrodes on plastic substrate while semiconductor and dielectric layers are printed by consecutive plate-to-roll gravure printing. Finally, inkjet printing of Ag organometallic ink is used to pattern the gate electrode. The fabricated OTFT exhibits excellent electrical performance, field-effect mobility over 0.2 cm²/Vs, which is one of the best compared to the previous works. The deposition of a self-assembled monolayer on the source-drain electrodes results in a higher work function which is suitable for a p-type polymer semiconductor. Moreover, the formation of dense gate electrode line on hydrophobic dielectric is achieved by selecting suitable Ag ink.     

Inkjet printed metallizations for Cu(In1−x Ga x )Se2 photovoltaic cells

This study reports the inkjet printing of Ag front contacts on Aluminum doped Zinc Oxide (AZO)/intrinsic Zinc Oxide (i‐ZnO)/CdS/Cu(In_1−xGa_x)Se₂ (CIGS)/Mo thin film photovoltaic cells. The printed Ag contacts are being developed to replace the currently employed evaporated Ni/Al bi‐layer contacts. Inkjet deposition conditions were optimized to reduce line resistivity and reduce contact resistance to the Al:ZnO layer. Ag lines printed at a substrate temperature of 200°C showed a line resistivity of 2.06 µΩ · cm and a contact resistance to Al:ZnO of 8.2 ± 0.2 mΩ · cm² compared to 6.93 ± 0.3 mΩ · cm² for thermally evaporated contacts. These deposition conditions were used to deposit front contacts onto high quality CIGS thin film photovoltaic cells. The heating required to print the Ag contacts caused the performance to degrade compared to similar devices with evaporated Ni/Al contacts that were not heated. Devices with inkjet printed contacts showed 11.4% conversion efficiency compared to 14.8% with evaporated contacts. Strategies to minimize heating, which is detrimental for efficiency, during inkjet printing are proposed. Copyright © 2011 John Wiley & Sons, Ltd.     

Direct Ink‐Jet Printing of Ag–Cu Nanoparticle and Ag‐Precursor Based Electrodes for OFET Applications

The field of organic electronics has seen tremendous progress over the last years and all‐solution‐based processes are believed to be one of the key routes to ultra low‐cost roll‐to‐roll device and circuit fabrication. In this regard a variety of functional materials has been successfully designed for inkjet printing. While orthogonal‐solvent approaches have frequently been used to tackle the solubility issue in multilayer solution processing, the focus of this work lies on printed metal electrodes for organic field‐effect transistors (OFET) and their curing concepts. Two metallic inkjet‐printable materials are studied: i) a silver‐copper nanoparticle based dispersion and ii) a soluble organic silver‐precursor. Photoelectron spectroscopy reveals largely metallic properties of the cured materials, which are compared with respect to OFET performance and process‐related issues. Contact resistance of the prepared metal electrodes is significantly larger than that of evaporated top‐contact gold electrodes. As direct patterning via inkjet printing limits the reliably achievable channel length to values well above 10 μm, the influence of contact resistance is rather small, however, and overall device performance is comparable.     

Programmable logic circuits for functional integrated smart plastic systems

In this paper, we present a functional integrated plastic system. We have fabricated arrays of organic thin-film transistors (OTFTs) and printed electronic components driving an electrophoretic ink display up to 70 mm by 70 mm on a single flexible transparent plastic foil. Transistor arrays were quickly and reliably configured for different logic functions by an additional process step of inkjet printing conductive silver wires and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) resistors between transistors or between logic blocks. Among the circuit functions and features demonstrated on the arrays are a 7-stage ring oscillator, a D-type flip-flop memory element, a 2:4 demultiplexer, a programmable array logic device (PAL), and printed wires and resistors. Touch input sensors were also printed, thus only external batteries were required for a complete electronic subsystem. The PAL featured 8 inputs, 8 outputs, 32 product terms, and had 1260 p-type polymer transistors in a 3-metal process using diode-load logic. To the best of our knowledge, this is the first time that a PAL concept with organic transistors has been demonstrated, and also the first time that organic transistors have been used as the control logic for a flexible display which have both been integrated on to a single plastic substrate. The versatility afforded by the additive inkjet printing process is well suited to organic programmable logic on plastic substrates, in effect, making flexible organic electronics more flexible.     

Printing-induced improvements of organic thin-film transistors

To understand the observation of improved pentacene (Pn) thin-film transistor mobility in flexible printed devices, a method for performing electrical measurements of organic thin-film transistors (OTFT) during the process of transfer printing has been developed. Different sample configurations were designed to test two aspects of the printing process: (1) the formation of the source/drain contacts a Pn thin-film, and (2) the formation of the transfer printed Pn/dielectric interface. In situ measurements show that pressure-induced contacts of gold (Au) electrodes result in a factor of seven mobility improvement compared with evaporation of top Au electrodes on an otherwise identical device configuration. Annealing the laminated device up to 90 °C caused no further improvement, and heating above 90 °C degraded performance. The mobility of a transfer printed device with the rough, as-grown top surface of the Pn in contact with the dielectric was found to increase dramatically with subsequent annealing for a sample temperature up to 120 °C. This is attributed to annealing-induced structural changes in the Pn film at elevated temperatures, consistent with X-ray bulk measurements showing enhanced crystal morphology in transfer printed Pn thin-films.     

Inkjetted crystalline single monolayer oligothiophene OTFTs

Crystalline monolayer films of a novel organic semiconducting material were deposited as the active layer for organic thin-film transistors (OTFTs) via inkjet printing. Devices exhibited field-effect mobilities up to 0.07 cm/sup 2//V/spl middot/s and on/off ratios >10/sup 8/, surpassing values measured for devices cast with thicker films of the same material. The printed monolayer devices exhibited superior subthreshold characteristics with less hysteresis, and defect and trap densities are improved over thicker film analogs. These results show that solution deposition techniques such as inkjet printing can result in the monolayer crystalline thin films that are requisite for near-ideal electrostatics in OTFTs.     

数字喷墨打印技术在PCB抗蚀层制作中的初步研究

随着数字喷墨打印设备和纳米油墨的不断发展,喷墨打印技术在PCB制作中得到了越来越广泛的应用。目前市场上主要包括三个方面的应用：抗蚀层、字符、阻焊。文章通过市场调研,成本评估和工艺能力评估重点研究了喷墨打印技术在线路抗蚀层制作中的应用。结果发现喷墨打印技术相对于传统的线路制作工艺具有一定的成本优势和线路制作能力。     

Polymer Inverter Fabricated by Inkjet Printing and Realized by Transistors Arrays on Flexible Substrates

We have fabricated organic thin-film transistors (OTFTs) and implemented inverters on flexible substrates using polythiophene (PHT) as the semiconductor and polyvinylphenol (PVP) as the gate dielectric. The semiconductor was defined by inkjet printing. The poor consistency of the printing process has affected the uniformity of inkjet-printed OTFTs enormously. We also proposed a method to increase the yield by incorporating a pre-testing step during circuit fabrication. We designed and fabricated a basic unit of circuits called a thin-film transistor (TFT) array. These devices were then connected to each other to form a gate via printed nano-silver. To verify the implementation flow, we designed and measured bootstrap inverters and ring oscillator composed of them. The five-stage ring oscillator has been fabricated and oscillated at the frequency, 60 Hz, when the supply voltage is 40 V      

A benchmark study of commercially available copper nanoparticle inks for application in organic electronic devices

A set of three commercial copper nanoparticle based inkjet inks has been benchmarked with respect to their potential to form conducting printed structures for future applications in organic electronic devices. Significant differences were observed in terms of jetting properties, spreading behaviour and line formation on a number of relevant substrates. The inks' stabilities against oxidation were investigated, inkjet printed patterns were subjected to photonic flash sintering and their electrical properties characterized. As a result, optimized conditions for printing and post-deposition processing were determined. Photonic flash sintering, which is a roll-to-roll compatible manufacturing process, allowed a significant reduction in sintering time. Flash sintering was performed in the presence of air, thereby excluding the necessity for processing under inert atmosphere. One product was identified which showed satisfactory performances regarding all tested features: stable jet formation, well-defined definition of the printed structures and high electrical conductivity (20% of the value of bulk Cu). The obtained results can be considered as a promising step towards the future application of Cu inks in organic electronic devices.     

Utilizing inkjet printing to fabricate electrical interconnections in a system-in-package

The printed interconnections for encapsulated electronic packages using nanoparticle metal inks and polymer dielectrics have been demonstrated. The printing has utilized a digital printing method, inkjet printing. The printing process has been adopted rather well, but process yield improvement required more attention to the control of individual manufacturing stages and error sources. The sources for possible errors can be roughly divided into separate groups: the substrate-ink interaction and treatment procedure related, ink jetting related, and moving stage related. In this paper, the individual stages were taken under consideration. The process performance was studied using statistical methods. The affecting factors were classified, and designed experiments were carried out to determine the most significant factors and to create a model to describe the behavior. According to the models, optimized process parameters were achieved, and implemented in practice.     

An MRI Receiver Coil Produced by Inkjet Printing Directly on to a Flexible Substrate

Inkjet printing has been used to produce resonant radio frequency coils that are comparable to those produced by conventional printed circuit board (PCB) methods. The coils, which consist of a conductive loop and in-series capacitors, form part of a receiver circuit that is used for magnetic resonance imaging (MRI). The resonant circuit is selective at the predetermined frequency of 400 MHz. The required electrical components (resistor, capacitor, and inductor) were produced by inkjet printing, with scaling experiments for resistor and capacitor performed before the complete loops with integrated capacitors were printed. Numerical simulation was used to determine the required values for the components. The inkjet printed circuit was combined with a small tuning and matching board before being connected to a network analyzer and the MRI hardware. With a matching of ${-}$ 38 dB at 400 MHz the achieved results were comparable to those from standard PCB techniques. The performance of the inkjet printed component as a receiver device for nuclear magnetic resonance and MRI was verified by imaging reference phantoms and a whole kiwifruit; it compares favorably to standard MRI devices. Inkjet printing can, therefore, be considered a feasible technique for producing MRI receiver circuits on flexible substrates.      

Degradation of all-inkjet-printed organic thin-film transistors with TIPS-pentacene under processes applied in textile manufacturing

Printed electronics represent an alternative solution for the manufacturing of low-temperature and large area flexible electronics. The use of inkjet printing is showing major advantages when compared to other established printing technologies such as gravure, screen or offset printing, allowing the reduction of manufacturing costs due to its efficient material usage and the direct-writing approach without requirement of any masks. However, several technological restrictions for printed electronics can hinder its application potential, e.g. the device stability under atmospheric or even more stringent conditions. Here, we study the influence of specific mechanical, chemical, and temperature treatments usually appearing in manufacturing processes for textiles on the electrical performance of all-inkjet-printed organic thin-film transistors (OTFTs). Therefore, OTFTs where manufactured with silver electrodes, a UV curable dielectric, and 6,13-bis(triisopropylsilylethynyl) pentance (TIPS-pentacene) as the active semiconductor layer. All the layers were deposited using inkjet printing. After electrical characterization of the printed OTFTs, a simple encapsulation method was applied followed by the degradation study allowing a comparison of the electrical performance of treated and not treated OTFTs. Industrial calendering, dyeing, washing and stentering were selected as typical textile processes and treatment methods for the printed OTFTs. It is shown that the all-inkjet-printed OTFTs fabricated in this work are functional after their submission to the textiles processes but with degradation in the electrical performance, exhibiting higher degradation in the OTFTs with shorter channel lengths (L = 10 μm).     

一种面向PCB的全印制电子技术

文章介绍了一种新兴的印制电子技术及其技术进展现状;概述了喷墨印制PCB加成法的技术特点,并就我国在印制电子技术的研发方面应采取的对策提出了一些建议。     

All-inkjet-printed low-pass filters with adjustable cutoff frequency consisting of resistors,inductors and transistors for sensor applications

Low-cost and flexible first and second order low-pass filters with adjustable cutoff frequency were designed and printed by inkjet printing technology. The all-inkjet-printed low-pass filters were characterized and an adjustable cutoff frequency feature in form of an inkjet-printed organic thin-film transistors (OTFTs) was added to the filters for application-oriented fine-tuning. The applicability of these small circuits was evaluated by signal filtering for sensor applications. As a result, low-pass filters with an adjustable cutoff frequency ranging from 82 Hz to 740 Hz were obtained, demonstrating their suitability in signal filtering and their promising applicability for tactile sensing characterized by low frequency signals.     

Polypyrrole top-contact electrodes patterned by inkjet printing assisted vapor deposition polymerization in flexible organic thin-film transistors

Highly conductive polymer, polypyrrole (PPy) was successfully patterned as source and drain (S/D) electrodes for flexible pentacene thin film transistors in top-contact structure by combining inkjet printing and vapor deposition polymerization. Facile inkjet printing of initiator and subsequent exposure of pyrrole monomers resulted in selective absorption and polymerization of pyrrole monomers on the patterned initiator region. Pentacene transistors based on printed PPy electrodes exhibited higher electrical characteristics than that of the devices with thermally evaporated Au electrodes. Improved performance of the devices based on PPy electrodes could be attributed to the reduction of contact resistance at the interface between polymer and organic semiconductor. For the replacement of metal electrodes, vapor deposition polymerization assisted inkjet printing technique can provide a versatile method to utilize highly conductive polymer as a functional electrode of flexible organic electronic devices.     

Inkjet Printing of a Highly Loaded Palladium Ink for Integrated,Low‐Cost pH Sensors

An inkjet printing process for depositing palladium (Pd) thin films from a highly loaded ink (>14 wt%) is reported. The viscosity and surface tension of a Pd‐organic precursor solution is adjusted using toluene to form a printable and stable ink. A two‐step thermolysis process is developed to convert the printed ink to continuous and uniform Pd films with good adhesion to different substrates. Using only one printing pass, a low electrical resistivity of 2.6 μΩ m of the Pd film is obtained. To demonstrate the electrochemical pH sensing application, the surfaces of the printed Pd films are oxidized for ion‐to‐electron transduction and the underlying layer is left for electron conduction. Then, solid‐state reference electrodes are integrated beside the bifunctional Pd electrodes by inkjet printing. These potentiometric sensors have sensitivities of 60.6 ± 0.1 and 57 ± 0.6 mV pH^?1 on glass and polyimide substrates, and short response times of 11 and 6 s, respectively. Also, accurate pH values of real water samples are obtained by using the printed sensors with a low‐cost multimeter. These results indicate that the facile and cost‐effective inkjet printing and integration techniques may be applied in fabricating future electrochemical monitoring systems for environmental parameters and human health conditions.     

有机绝缘层材料聚(4-乙烯基苯酚)喷墨打印工艺研究

通过压电喷墨打印方式在氧化铟锡(ITO)玻璃上直接图案化打印聚(4-乙烯基苯酚)(PVP),研究了不同浓度PVP的电学特性,从电容、漏电流、击穿场强几个方面进行了分析。结果表明,采用打印方式得到的PVP绝缘层在0～40V的外加电压下,漏电流密度在10-11～10-8 A/cm2范围内,为打印方式制备高性能交联PVP(CL-PVP)介电层提供了必要的参考。     

Inkjet Process for Conductive Patterning on Textiles: Maintaining Inherent Stretchability and Breathability in Knit Structures

In this work, a novel technique of inkjet printing e‐textiles with particle free reactive silver inks on knit structures is developed. The inkjet‐printed e‐textiles are highly conductive, with a sheet resistance of 0.09 Ω sq^‐1, by means of controlling the number of print passes, annealing process, and textile structures. It is notable that the inkjet process allows textiles to maintain its inherent properties, including stretchability, flexibility, breathability, and fabric hand after printing process. This is achieved by formation of ultrathin silver layers surrounding individual fibers. The silver layers coated on fibers range from 250 nm to 2.5 µm, maintaining the size of interstices and flexibility of fibers. The annealing process, structure of fibers, and printed layers significantly influence the electrical conductivity of the patterned structures on textiles. Outstanding electrical conductivity and durability are demonstrated by optimizing print passes, controlling textile structures, and incorporating an in situ annealing process. The electrical resistance dependence on the strain rate of the textiles is examined, showing the ability to maintain electrical conductivity to retain light‐emitting diode use, stable more than 500 consecutive strain cycles. Most importantly, inkjet‐printed e‐textiles maintain their characteristic washability, breathability, and fabric hands for applications in wearable technology.