Photonic Sintering Research Articles

3D Printing of Highly Electrically Conductive Zinc for Sustainable Electronics Applications

AbstractThe increasing use of electronic devices raises concerns about resource availability and end‐of‐life management, particularly regarding conductors for interconnects and sensing elements. While gold and silver are the leading materials for interconnects, they pose challenges related to scarcity, cost, and toxicity. Zinc offers a promising alternative due to its good electrical conductivity, non‐toxicity, abundance, and affordability. However, challenges in achieving high conductivity and waste generation from processing techniques like screen‐printing remain. To address this, a zinc ink optimizes for 3D printing is proposed, using active zinc particles in a shellac matrix. The methods, including chemical and photonic sintering, achieve conductivities of up to 8.74•104 S m⁻¹ on paper substrates, with stable performance over a range of 30%–70% relative humidity at 15, 20, 25, and 30 °C respectively. Potential applications in high‐conductivity transducers for humidity sensing and metal‐air batteries are demonstrated, achieving a maximum power output of 3.5 mW and an open‐circuit voltage of 1.25 V. The integration of digital material assembly of zinc, reliable high‐performance operation, and non‐toxicity pave the way for innovative advancements in sustainable electronics, including applications in environmental sensing, e‐textiles, and healthcare.

Photonic post-processing of a multi-material transparent conductive electrode architecture for optoelectronic device integration.

Emerging flexible optoelectronic devices require multi-material processing capabilities to fully enable the use of temperature-sensitive substrates and materials. This report demonstrates how photonic sintering enables the processing of materials with very different properties. For example, charge carrier transport/blocking metal-oxides, and transparent conductive silver nanowire-based electrodes ought to be compatible with low-energy and high-throughput processing for integration onto flexible low-temperature substrates. Compared to traditional post-processing methods, we show a rapid fabrication route yielding highly-stable hybrid electrode architectures on polyethylene terephthalate (PET). This architecture consists of an interconnected silver nanowire network encapsulated with a thin crystalline photo-sensitive titanium dioxide (TiO2) coating, allowing both layers to be treated using independent photonic post-processing sintering steps. The first step sinters the nanowires, while the second completes the conversion of the top metal-oxide layer from amorphous to crystalline TiO2. This approach improves on the fabrication speed compared to oven processing, while delivering optical and electrical characteristics comparable to the state of the art. Optimized transparency values reach 85% with haze values down-to 7% at 550 nm, while maintaining a sheet resistance of 18.1 Ω sq.-1. However, this hybrid architecture provides a much stronger resilience to degradation, which we demonstrate through exposure to harsh plasma conditions. In summary, this study shows how carefully-optimized photonic curing post-processing can provide more-stable hybrid architectures while using a multi-material processing technique suitable for high-volume manufacturing on low-temperature substrates.

Blacklight sintering of garnet-based composite cathodes

Garnet-structured Li7La3Zr2O12 (LLZO) is an attractive electrolyte for lithium solid-state batteries (SSBs), but its processing requires long sintering at temperatures above 1000 °C to achieve sufficient ionic conductivity. Such sintering is not only time and energy consuming, but also leads to undesirable material interactions. Therefore, a significant reduction of the sintering time is very important for the future development of garnet-based batteries. A promising method is the recently introduced photonic blacklight sintering with light sources in the UV spectrum, which enables energy-efficient sintering of ceramic layers within seconds. In this work, blacklight sintering of garnet-based SSBs is validated using a model cell consisting of LLZO and LiCoO2 (LCO) composite cathode layers printed on dense LLZO pellets. An optimized sintering program allowed the production of working cells in only 20 s. This study demonstrates the suitability of blacklight sintering for processing garnet-based SSBs and provides guidance for future process optimization.

Photonic sintering of copper for rapid processing of thick film conducting circuits on FTO coated glass

Copper potentially provides a cost-effective replacement for silver in printed electronic circuitry with diverse applications in healthcare, solar energy, IOT devices and automotive applications. The primary challenge facing copper is that it readily oxidizes to its non-conductive state during the sintering process. Photonic sintering offers a means of overcoming the oxidation by which rapid conversion from discrete nano-micro particles to fully or partially sintered products occurs. An experimental study of flash lamp sintering of mixed nano copper and mixed nano/ micro copper thick film screen printed structures on FTO coated glass was carried out. It shows that there may be multiple energy windows which can successfully sinter the thick film copper print preventing detrimental copper oxidation. Under optimum conditions, the conductivities achieved in under 1 s was (3.11–4.3 × 10–7 Ω m) matched those achieved in 90 min at 250 °C under reducing gas conditions, offering a significant improvement in productivity and reduced energy demand. Also present a good film stability of a 14% increase in line resistance of 100 N material, around 10% for the 50N50M ink and only around 2% for the 20N80M.

A Perspective on Emerging and Future Sintering Technologies of Ceramic Materials

Novel sintering methods have emerged in the recent past years, which have raised great interest in the scientific community. Relying on electric field effects, high heating rates, the use of mechanical pressure, or hydrothermal conditions, they offer fundamental advantages compared to conventional sintering routes like minimizing the energy consumption and enhancing the process efficiency. This perspective aims at explaining these effects in a general way and presenting the status quo of using them for the processing of high‐performing ceramic materials. In detail, this work focuses on flash sintering, ultrafast high‐temperature sintering, spark plasma sintering, cold sintering, and photonic sintering methods based on different light sources. The specificities, potentials, and limitations of each method are compared, especially in the light of a possible industrialization.

High-performance printed electrode with rapid fabrication based on UV and IPL light processes without thermal treatment

We developed flexible and ultraviolet (UV)-curable electrodes with improved electrical conductivity using two light processes. Existing microparticle electrodes have poor durability. In this study, we improved electrode durability by facilitating UV light transmission using nanosilver particles and increased electrical conductivity using the photonic sintering process as a posttreatment process. The formulation of the UV-curable nanosilver paste developed this way had no problem in the cross-cut tape test and showed excellent pencil hardness (>3H). Furthermore, the electrical resistivity was 2.76 × 10−5 Ω·cm, and the resistance change rate was <1 % even after 50,000 times of repetitive tests with a 3-mm radius of curvature. When twelve electrode patterns with LED installation and bent were manufactured, we confirmed that there was no change in brightness. Finally, as polyethylene terephtalate, a low-temperature substrate, was not damaged even after the process was completed, the paste and process showed sufficient performance even in the low-temperature process.

Vertical-cavity surface-emitting laser (VCSEL)-based ultrafast photonic sintering of solid oxide fuel cells (SOFCs): prospects for time-efficient/two-dimensional scalability to large-sized SOFCs

980 nm VCSEL illumination eliminates the organic additives and densifies the laminated multilayered SOFC NiO–YSZ|NiO–ScCeSZ|ScCeSZ|GDC|GDCscaffold in just 2.42 h compared to &gt;100 h needed for the conventional thermal sintering process.

Process Development for Printed Copper With Surface Mount Devices on Inkjet Metallization

Abstract Printed electronics is a fastest growing and emerging technology that have shown much potential in several industries including automotive, wearables, healthcare, and aerospace. Its applications can be found not only in flexible but also in large area electronics. The technology provides an effective and convenient method to additively deposit conductive and insulating materials on any type of substrate. Despite its status, it is not without its challenges. Inkjet technology has gained much attention due to its low cost, low-material consumption, and capability for mass manufacturing. The preferred conductive metal of choice has been mostly silver due to its excellent electrical properties and ease in sintering. However, silver comes to be expensive than its counterpart copper. Since copper is prone to oxidation, much focus has been given toward photonic sintering that involves sudden burst of pulsed light at certain energy to sinter the copper nanoparticles. With this technique, only the printed material gets sintered in a matter of seconds without having a great impact on its substrate. With all the knowledge, there is still a large gap in the process side with copper where it is important to look how the print process affects the electrical and mechanical properties of copper. With the process developed, the resistivity of printed copper was found to be five times the bulk copper. In regards to adhesion to the polyimide film, mechanical shear load to failure was found to be within 15–20 gF. To demonstrate the complete process, commercial-off-the-shelf components are also mounted on the additively printed pads. Statistically, control charting technique is implemented to understand any process variation over long duration of prints.

High-conductivity screen-printable silver nanowire Ink for optically transparent flexible radio frequency electronics

Optically transparent conductors have paved the way in various optoelectronic and radio frequency devices where high electrical conductivity and optical transparency with mechanical flexibility, as well as large area fabrication are deemed necessary. Printing techniques are viable for fabricating large-area devices with high mechanical flexibilities. However, the preparation of suitable inks and printing recipes is essential to achieve a high electrical conductivity and transparency. In this study, the best tradeoff between conductivity and optical transmittance was achieved through silver (Ag) nanowires (NWs)-based ink formulation with tuned Ag NW loading, solvent compositions and polymer weight percentages. The ink was deposited through screen-printing, which enabled a large-area and high-resolution patterning of the AgNWs. The washing time of the post-printed films exhibited a decisive effect on the initial conductivity, which was further improved through photonic sintering. During the photonic sintering, the voltages, pulse lengths (μs) and fire rates (Hz) were optimized to obtain the best conductivity of the printed films. Maximum optical transparencies of 78% and 83% were achieved for the conductivities of ∼5.88 × 106 and ∼6.25 × 106 S m−1, respectively. As a proof of concept, a fully printed optically transparent antenna was realized that could operate in a wide frequency band suitable for high-data-rate wireless communication.

Photonic Sintering of Oxide Ceramic Films: Effect of Colored FexOy Nanoparticle Pigments

Alumina and zirconia thin films modified with colored nano-FexOy pigments were sintered by the flash-lamp-annealing method. We selected a nano α-Al2O3 and micron α-Al2O3 bimodal mixture as the base precursor material, and we doped it with 5 vol% of FexOy red/brown/black/yellow pigments. The coatings were deposited from nanoparticle dispersions both on glass and on flexible metal foil. The characteristics of the thin films obtained with the use of various additives were compared, including the surface morphologies, optical properties, crystallinities, and structures. Flash lamp annealing was applied with the maximum total energy density of 130 J/cm2 and an overall annealing time of 7 s. Based on the simulated temperature profiles and electron-microscopy results, a maximum annealing temperature of 1850 °C was reached for the red Al2O3: Fe2O3 ceramic film. The results show that red α-Fe2O3 pigments allow for the achievement of maximum layer absorption, which is effective for flash lamp sintering. It was also possible to use the selected red α-Fe2O3 particles for the flash-lamp-assisted sintering of ZrO2 on a 30 µm-thin flexible stainless-steel substrate.

(Invited) Scalable Printing of Flexible/Wearable Energy and Sensor Systems

Nanoscale materials are attractive and promising building blocks for a broad range of emerging technologies due to their unique and superior properties compared to the bulk form. However, converting nanoscale materials into high-performing functional systems while translating their unique properties from nanoscale to macroscale remain a major challenge due to many scientific and technological obstacles.This talk will focus on our research on developing versatile and synergistic additive manufacturing and nanomanufacturing methods to manufacture and transform a broad range of emerging functional nanomaterials into innovative and sustainable energy and sensor systems in a highly scalable, controllable and affordable manner. This talk will present our recent research progresses scalable printing and photonic sintering to fabricate flexible thermoelectric generator (f-TEG) for energy harvesting. Our printed p-type and n-type flexible films demonstrate peak thermoelectric figure of merit ZT greater than unity near room temperature, which is among the highest reported ZT values in flexible thermoelectric materials. In addition, this talk will also present a novel hybrid printing method that can integrate functional materials and soft structural materials and fabricate highly stretchable and wearable sensors for a broad range of physical and chemical sensing applications.

Multi-objective optimization of intense pulsed light sintering process for aerosol jet printed thin film

The sintering of printed nanoparticle films is a necessary processing step for most nanoparticle inks to make the printed film functional. The sintering of nanoparticle is usually performed through thermal sintering, photonic sintering, induction sintering, etc. Intense pulsed light (IPL) sintering method is one of the most popular sintering methods for nanoparticle inks due to the fast and effective process, but it may yield mediocre performance if improper sintering parameters are used. In this work, we investigate the correlation between the two factors which are the print passes of aerosol jet printing and the sintering distance of the samples on the effect of the surface morphology and sheet resistance. A contradictory correlation between the two factors was observed and a multi-objective optimization was carried out using machine learning method to identify the most optimum conditions for both factors. We found that multi-objective optimization approach is effective in reducing the conflicting responses, thus the sintered thin film can have low sheet resistance and low surface roughness. This work provides an essential guide for achieving conductive films with electrical conductivity and low surface roughness using IPL sintering process for fast fabrication of multi-layered electronics such as electrochemical electrodes.

Multi-objective optimization of intense pulsed light sintering process for aerosol jet printed thin film

The sintering of printed nanoparticle films is a necessary processing step for most nanoparticle inks to make the printed film functional. The sintering of nanoparticle is usually performed through thermal sintering, photonic sintering, induction sintering, etc. Intense pulsed light (IPL) sintering method is one of the most popular sintering methods for nanoparticle inks due to the fast and effective process, but it may yield mediocre performance if improper sintering parameters are used. In this work, we investigate the correlation between the two factors which are the print passes of aerosol jet printing and the sintering distance of the samples on the effect of the surface morphology and sheet resistance. A contradictory correlation between the two factors was observed and a multi-objective optimization was carried out using machine learning method to identify the most optimum conditions for both factors. We found that multi-objective optimization approach is effective in reducing the conflicting responses, thus the sintered thin film can have low sheet resistance and low surface roughness. This work provides an essential guide for achieving conductive films with electrical conductivity and low surface roughness using IPL sintering process for fast fabrication of multi-layered electronics such as electrochemical electrodes.

Rapid thermal sintering of screen-printed LiCoO2 films

A rapid photonic sintering process (rapid thermal processing) was used to obtain compact films of cathode active material of lithium batteries. LiCoO2 (LCO) thick films were screen-printed on a steel substrate followed by a contactless thermal processing at 1000 °C in only 90 s. A homogenous densification of such layers could be verified by scanning electron microscopy, while the structural consistency of the LCO phase in these layers could be detected by X-ray diffraction and Raman spectroscopy. Furthermore, electrochemical activity of the layer was confirmed by electrochemical cell tests with a liquid electrolyte.

Large‐Area Transient Conductive Films Obtained through Photonic Sintering of 2D Materials (Adv. Mater. Technol. 2/2022)

Photonic Sintering Approach Using a novel microfabrication approach based on anodic aluminum oxide templates, Xian Huang and colleagues develop a photonic sintering approach to achieve large-area conductive van der Waals transient films and electronics in article 2100439. The techniques allow selectively transfering 2D materials with controllable thicknesses and definable patterns from temporal plastic substrates onto bioresorbable substrates.

Hierarchical copper nanostructures synthesized on microparticles for improved photothermal conversion in photonic sintering of copper-based printed electrodes

Photonic sintering of Cu-particle-based printed patterns using intense pulsed light (IPL) is a promising route to the large-scale fabrication of printed electronics for commercial applications.

A Hierarchical Metal Nanowire Network Structure for Durable, Cost-Effective, Stretchable, and Breathable Electronics.

Polymer nanofiber-based porous structures ("breathable devices") have been developed for breathable epidermal electrodes, piezoelectric nanogenerators, temperature sensors, and strain sensors, but their applications are limited because increasing the porosity reduces device robustness. Herein, we report an approach to produce ultradurable, cost-effective breathable electronics using a hierarchical metal nanowire network and an optimized photonic sintering process. Photonic sintering significantly reduces the sheet resistance (16.25 to 6.32 Ω sq-1) and is 40% more effective than conventional thermal annealing (sheet resistance: 12.99 Ω sq-1). The mechanical durability of the sintered (648.9 Ω sq-1) sample is notably improved compared to that of the untreated (disconnected) and annealed (19.1 kΩ sq-1) samples after 10,000 deformation cycles at 40% tensile strain. The sintered sample exhibits ∼29 times less change in electrical performance compared to the thermally annealed sample. This approach will lead to the development of affordable and ultradurable commercial breathable electronics.

Printed Electrode for High-Performance Bow-Tie Antenna by Photonic Sintering Process

Recently, flexible electronic device technology has evolved beyond curved devices with the development of flexible/stretchable devices that can be crumpled or stretched. Both elasticity and durability are essential for these devices, which should have high-conductivity for antennas and repeatability for sensors. In addition, electronic-skins, which can have a direct impact on the human-body, should be harmless to the human-body and should not be deformed by contact with sweat or organic matter. In this study, PDMS substrates were used to satisfy the above conditions. PDMS is used to fabricate human-friendly, flexible/stretchable substrates, and it has excellent repeat durability characteristics. To improve the adhesion of these PDMS films and electrodes, conductive paste was produced based on PDMS resins of the same properties. In addition, two types of Ag particles were selected as conductive fillers because the electrode characteristics of the antenna application requires excellent conductivity, and conductive paste were produced using flake Ag, which could affect conductivity, and Ag nanoparticles that affect stretchability and repeatability. The paste was applied using a high-efficiency printing technique. The printed electrodes were cured in a thermal oven. For higher conductivity, photonic-sintering was carried out during post-processing. As a result, 1.1117×106 (S/m) had excellent conductivity, performed well in repeated tensile-durability experiments of 30% to 100 times, and produced a bow-tie antenna for the above electrodes. As a result of tensing up to 35% through a Network-Analyzer, there was no performance change in the resonance-frequency or return-loss values, and excellent electrodes were developed that would achieve excellent performance even if they are applied in the sub-frequency area of 5G-antennas in the future.

Combustion‐Assisted Photonic Sintering of Printed Liquid Metal Nanoparticle Films

AbstractLiquid metals are ideally suited for flexible and wearable electronics due to their compatibility with additive manufacturing and high electrical conductivity that is maintained following mechanical perturbation. While printing of eutectic gallium–indium (eGaIn) liquid metal nanoparticles has been demonstrated, previous techniques for activating electrical conductivity in the as‐printed insulating eGaIn nanoparticles limit throughput in roll‐to‐roll manufacturing processes. Here, ultrafast photonic sintering of eGaIn nanoparticles is demonstrated, which is further enhanced through the use of nitrocellulose as a carrier polymer that undergoes optically triggered combustion to produce eGaIn thin films with electrical conductivities exceeding 104 S cm–1. This combustion‐assisted photonic sintering (CAPS) is two orders of magnitude faster than previously demonstrated noncontact sintering techniques. By circumventing the established tradeoff between electrical conductivity and activation speed, CAPS will facilitate the use of eGaIn liquid metal nanoparticles in high‐throughput additive manufacturing of flexible and wearable electronics, sensors, and related technologies.

Development of ecoflex based nano silver paste through photonic sintering process

Development of ecoflex based nano silver paste through photonic sintering process