Low-Cost Fabrication of Printed Electronics Devices through Continuous Wave Laser-Induced Forward Transfer

Selective Metallization on Ordinary Polymer Substrates by Laser Direct Activation of Copper Phosphate or Nickel Phosphate

In recent years, selective metallization on polymer surfaces has attracted considerable attention due to its excellent properties and wide applications. This paper reports that copper phosphate (Cu₃(PO₄)₂) or nickel phosphate (Ni₃(PO₄)₂) was selected as laser-active material to successfully fabricate metallic patterns on ordinary polymer substrates by laser direct activation and electroless plating. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were utilized to characterize the interaction mechanism between a nanosecond-pulsed laser (355 and 1064 nm wavelengths) and Cu₃(PO₄)₂ or Ni₃(PO₄)₂. It was found that after 355 or 1064 nm laser activation with appropriate parameters, Cu⁺ was generated from Cu₃(PO₄)₂, and NiO was generated from Ni₃(PO₄)₂. At the same time, Cu⁺ or NiO adsorbed on the porous sponge-like microstructure of modified polycarbonate (PC), respectively, and acted as catalytic active centers to realize selective copper deposition in the laser-activated zone. Furthermore, the obtained copper layers were confirmed to possess good selectivity, electrical conductivity, and high adhesion strength (the highest grade of 5B). Moreover, from comparisons of Cu₃(PO₄)₂ with Ni₃(PO₄)₂ and of 355 nm laser activation with 1064 nm laser activation, the 1064 nm laser activation of Cu₃(PO₄)₂ produced the most catalytic seeds (Cu⁺) and had the best catalytic effect.

Printing via Laser-Induced Forward Transfer and the Future of Digital Manufacturing

In the last decades, digital manufacturing has constituted the headline of what is starting to be known as the 'fourth industrial revolution', where the fabrication processes comprise a hybrid of technologies that blur the lines between fundamental sciences, engineering, and even medicine as never seen before. One of the reasons why this mixture is inevitable has to do with the fact that we live in an era that incorporates technology in every single aspect of our daily lives. In the industry, this has translated into fabrication versatility, as follows: design changes on a final product are just one click away, fabrication chains have evolved towards continuous roll-to roll processes, and, most importantly, the overall costs and fabrication speeds are matching and overcoming most of the traditional fabrication methods. Laser-induced forward transfer (LIFT) stands out as a versatile set of fabrication techniques, being the closest approach to an all-in-one additive manufacturing method compatible with virtually any material. In this technique, laser radiation is used to propel the material of interest and deposit it at user-defined locations with high spatial resolution. By selecting the proper laser parameters and considering the interaction of the laser light with the material, it is possible to transfer this technique from robust inorganic materials to fragile biological samples. In this work, we first present a brief introduction on the current developments of the LIFT technique by surveying recent scientific review publications. Then, we provide a general research overview by making an account of the publication and citation numbers of scientific papers on the LIFT technique considering the last three decades. At the same time, we highlight the geographical distribution and main research institutions that contribute to this scientific output. Finally, we present the patent status and commercial forecasts to outline future trends for LIFT in different scientific fields.

Printing Technologies as an Emerging Approach in Gas Sensors: Survey of Literature

Herein, we review printing technologies which are commonly approbated at recent time in the course of fabricating gas sensors and multisensor arrays, mainly of chemiresistive type. The most important characteristics of the receptor materials, which need to be addressed in order to achieve a high efficiency of chemisensor devices, are considered. The printing technologies are comparatively analyzed with regard to, (i) the rheological properties of the employed inks representing both reagent solutions or organometallic precursors and disperse systems, (ii) the printing speed and resolution, and (iii) the thickness of the formed coatings to highlight benefits and drawbacks of the methods. Particular attention is given to protocols suitable for manufacturing single miniature devices with unique characteristics under a large-scale production of gas sensors where the receptor materials could be rather quickly tuned to modify their geometry and morphology. We address the most convenient approaches to the rapid printing single-crystal multisensor arrays at lab-on-chip paradigm with sufficiently high resolution, employing receptor layers with various chemical composition which could replace in nearest future the single-sensor units for advancing a selectivity.

Laser-based three-dimensional manufacturing technologies for rechargeable batteries

Laser three-dimensional (3D) manufacturing technologies have gained substantial attention to fabricate 3D structured electrochemical rechargeable batteries. Laser 3D manufacturing techniques offer excellent 3D microstructure controllability, good design flexibility, process simplicity, and high energy and cost efficiencies, which are beneficial for rechargeable battery cell manufacturing. In this review, notable progress in development of the rechargeable battery cells via laser 3D manufacturing techniques is introduced and discussed. The basic concepts and remarkable achievements of four representative laser 3D manufacturing techniques such as selective laser sintering (or melting) techniques, direct laser writing for graphene-based electrodes, laser-induced forward transfer technique and laser ablation subtractive manufacturing are highlighted. Finally, major challenges and prospects of the laser 3D manufacturing technologies for battery cell manufacturing will be provided.

Experimental investigation of the jet-on-jet physical phenomenon in laser-induced forward transfer (LIFT)

Understanding the physics behind the ejection dynamics in laser-induced forward transfer (LIFT) is of key importance in order to develop new printing techniques and overcome their limitations. In this work, a new jet-on-jet ejection phenomenon is presented and its physical origin is discussed. Time-resolved shadowgraphy imaging was employed to capture the ejection dynamics and is complemented with the photodiode intensity measurements in order to capture the light emitted by laser-induced plasma. A focus scan was conducted, which confirmed that the secondary jet is ejected due to laser-induced plasma generated at the center of the laser spot, where intensity is the highest. Five characteristic regions of the focus scan, with regards to laser fluence level and laser spot size, were distinguished. The study provides new insights in laser-induced jet dynamics and shows the possibility of overcoming the trade-off between the printing resolution and printing distance.

Laser-Induced Forward Transfer: A Method for Printing Functional Inks

Laser-induced forward transfer (LIFT) is a direct-writing technique based in the action of a laser to print a small fraction of material from a thin donor layer onto a receiving substrate. Solid donor films have been used since its origins, but the same principle of operation works for ink liquid films, too. LIFT is a nozzle-free printing technique that has almost no restrictions in the particle size and the viscosity of the ink to be printed. Thus, LIFT is a versatile technique capable for printing any functional material with which an ink can be formulated. Although its principle of operation is valid for solid and liquid layers, in this review we put the focus in the LIFT works performed with inks or liquid suspensions. The main elements of a LIFT experimental setup are described before explaining the mechanisms of ink ejection. Then, the printing outcomes are related with the ejection mechanisms and the parameters that control their characteristics. Finally, the main achievements of the technique for printing biomolecules, cells, and materials for printed electronic applications are presented.

Continuous-Wave Laser-Induced Transfer of Metal Nanoparticles to Arbitrary Polymer Substrates

Laser-induced forward transfer (LIFT) and selective laser sintering (SLS) are two distinct laser processes that can be applied to metal nanoparticle (NP) ink for the fabrication of a conductive layer on various substrates. A pulsed laser and a continuous-wave (CW) laser are utilized respectively in the conventional LIFT and SLS processes; however, in this study, CW laser-induced transfer of the metal NP is proposed to achieve simultaneous sintering and transfer of the metal NP to a wide range of polymer substrates. At the optimum laser parameters, it was shown that a high-quality uniform metal conductor was created on the acceptor substrate while the metal NP was sharply detached from the donor substrate, and we anticipate that such an asymmetric transfer phenomenon is related to the difference in the adhesion strengths. The resultant metal electrode exhibits a low resistivity that is comparable to its bulk counterpart, together with strong adhesion to the target polymer substrate. The versatility of the proposed process in terms of the target substrate and applicable metal NPs brightens its prospects as a facile manufacturing scheme for flexible electronics.

Blue Laser Projection Printing of Conductive Complex 2D and 3D Metallic Structures from Photosensitive Precursors

Photosensitive precursors are developed for the printing of 2D and 3D conductive structures via blue laser projection printing. With the assistance of a photosensitizer, metal nanoparticles can be efficiently photosynthesized under laser irradiation of low light intensity (45-290 mW cm^-2). By projecting well-defined laser patterns on the precursor, corresponding 2D metal structures with the finest line of about 50 μm can be formed on various substrates including flexible polymer thin films, curved substrates, and ground glass. Moreover, complex 3D objects with nanoparticles embedded in the polymeric matrix are constructed via 3D printing combining photoreduction of the metal precursor and photopolymerization of resin. The as-prepared structures exhibit promising conductivities after sintering (in the order of magnitude of 10⁶ S m^-1). A possible mechanism of photochemical synthesis of metal nanoparticles upon exposure to blue laser is proposed. The high efficiency and low cost of the technique, the complexity of the structures prepared, and the applicability to various substrates and metals (including silver, gold, and palladium) promise practical applications of this approach in the printed electronics industry.

Heterogeneous Integration of Three-Primary-Color Photoluminescent Nanoparticle Arrays with Defined Interfaces

Minimized photoluminescent devices require both high-density fluorescent arrays and minimal cross-talk between neighboring pixels on the limited area. However, the challenges to achieve the overall integration of nanomaterial-based devices hinder the development of microscale full-color displays, including micro/nanoarray density, orientation control, multimaterial interface morphology, and uniform colors. Here, we report a heterogeneous integration approach to control the orientation, combination, and density of fluorescent micro/nanoarrays on flexible substrates. By controlling the defined interface and critical shrinkage width of liquid bridges, the width of three-primary-color micro/nanolines reached 100 nm. The interval between two parallel luminous lines is down to 40 μm, and the optical cross-talk effect is remarkably reduced. This work provides a facile approach to prepare high-performance micro-photoluminescent and imaging arrays for next-generation flexible display and lighting technology.

Spraying dynamics in continuous wave laser printing of conductive inks

Laser-induced forward transfer (LIFT), though usually associated with pulsed lasers, has been recently shown to be feasible for printing liquid inks with continuous wave (CW) lasers. This is remarkable not only because of the advantages that the new approach presents in terms of cost, but also because of the surprising transfer dynamics associated with it. In this work we carry out a study of CW-LIFT aimed at understanding the new transfer dynamics and its correlation with the printing outcomes. The CW-LIFT of lines of Ag ink at different laser powers and scan speeds revealed a range of conditions that allowed printing conductive lines with good electrical properties. A fast-imaging study showed that liquid ejection corresponds to a spraying behavior completely different from the jetting characteristic of pulsed LIFT. We attribute the spray to pool-boiling in the donor film, in which bursting bubbles are responsible for liquid ejection in the form of projected droplets. The droplet motion is then modeled as the free fall of rigid spheres in a viscous medium, in good agreement with experimental observations. Finally, thermo-capillary flow in the donor film allows understanding the evolution of the morphology of the printed lines with laser power and scan speed.