Aerosol Jet Printed Research Articles

Realizing Arbitrary 3D Microarchitectures with Curved and near-Sharp Segments via Toolpath Strategies in Aerosol Jet Printing

Aerosol Jet (AJ) printing is a jetting-based additive manufacturing (AM) technique that uses droplets in an aerosol form to deposit nanoparticles or polymer inks at a length scale of about 10 micrometers. The desired structural geometries via AJ printing can be obtained at a high efficiency and accuracy by engineered toolpaths and fill strategies. Recently, AJ printing is used to create three-dimensional (3D) freestanding microarchitectures such as microlattices, spirals, walls, and micropillars without any auxiliary support during printing. In this work, we demonstrate that for curved segments, the difference in the printed material volume on the convex side vs concave side leads to the accumulation of material while building freestanding 3D microarchitectures. This effect is most severe for sharp corners, which leads to build-defects such as protrusions and voids. We carry out a systematic study of the material accumulation on curved segments of AJ printed 3D microarchitectures. For 3D microwall segments with sharp curved portions, a positive (or negative) material accumulation causing large overgrowths (or voids) as a function of the angle between the tangents on the two sides of the microwalls and the radii of curvature are studied. For sharp bends (<15°) in the microwalls, adding a radius of curvature may not be sufficient to avoid overgrowths and voids, and the lines can be considered as individual segments. For microwall bends with >45°, smaller radii of curvature can be tolerated. We conclude that a fillet radius equal to the line width for 30° angles is necessary to avoid accumulation and therefore the protrusion defects. A simple model based on mass-conservation is also developed which shows the importance of considering ink self-leveling during printing. This information is then used for toolpath strategies to avoid defects on sharp curved microwall segments for complex 3D architectures such as protruding star shape and Scotty Dog, the Carnegie Mellon University mascot. This research will enable the defect-free fabrication of highly complex 3D microarchitectures via jetting-based AM techniques such as AJ printing.

Aerosol Jet and Inkjet Printing Methods for Die-Level Packaging of Custom MEMS Devices

Abstract In this study, we propose an alternative, low-cost, packaging method using both inkjet and aerosol jet printing to fabricate functional interconnects for custom die-level packages assembled on Printed Circuit Boards (PCB). Our process involves the manufacturing of a stacked structure with insulating and conducting layers, fabricated using inkjet and aerosol jet printing, respectively. In the first part of the study, we characterized UV adhesive deposition on the standard resin-coated PCB to acquire the optimal parameters necessary for the fabrication of the insulating layer with thicknesses around 100 μm. In the second part of our study, we developed a precise method for printing silver conducting lines using an aerosol jet printer, enabling the realization of structures with features as small as 50 microns on non-planar surfaces. The insulating part of the MEMS/PCB structure serves as a ramp ensuring continuity of the aerosol jet printed connection between the PCB and the Si die. A 1 cm x 1 cm Si chip with a custom MEMS microrobot was used to demonstrate the feasibility and flexibility of our approach in practice. After fabrication, we evaluated the interconnects for conductivity and repeatability. The packaging and inspection process was carried out using Nexus, a unique robotic system integrating additive manufacturing, robotic transport, and metrology. The results show that we successfully fabricated printed interconnects between copper PCB pads and Si die cleanroom fabricated gold pads, while electrical characterization revealed resistances in the range of 1 Ω - 10 Ω. Our approach can be utilized in the manufacturing of electrical interconnects for custom devices on different substrates, including traditional and flexible PCBs. Furthermore, the applied printing techniques enable the use of other insulating or conducting inks and the formation of structures of custom geometries across a wide range of scales - 20 μm to 1 mm.

Enhancing the quality factor of aerosol jet printed RF spiral inductors through gold electroplating

Aerosol jet printing (AJP) outperforms inkjet printing by significantly reducing printed line width, effectively addressing issues such as bulging and surface irregularities. This technology allows for line widths as narrow as 10–100 μm with high aspect ratios, making it well-suited for radio frequency (RF) applications. Consequently, AJP emerges as a valuable tool for direct printing in RF applications. Among conductive inks, silver nanoparticle (Ag-NP) ink is preferred for its straightforward direct printing process and lower sintering temperature requirements. However, the conductivity of printed Ag NP traces falls markedly below that of bulk silver due to significant porosity, limiting its use in RF applications where a high-quality factor is essential. The quality factor of an inductor, indicative of its efficiency in energy storage and release, inversely correlates with its resistance. Our research combines AJP with selective electroplating to reduce the resistance of printed traces, thereby enhancing the inductor’s quality factor for RF applications. We fabricated spiral inductors on alumina substrates using silver NP ink and subsequently applied selective gold electroplating to these traces. This approach led to a significant increase in the inductors’ quality factor, improving it by a factor of 3–5 in the RF frequency range of 100–700 MHz.

Titanium Dioxide Nanomaterial Ink Production Through Laser Ablation Synthesis in Solution for Printed Electronics Applications

Flexible and printed electronics have become increasingly popular as they make possible the production of flexible, low‐cost, multifunction devices that are unachievable through traditional manufacturing methods. The printed films are significantly impacted and thus limited by the existing ink production process. Herein, an alternate technique of generating high‐quality titanium dioxide (TiO2) nanoparticle ink compatible with aerosol jet printing using laser ablation synthesis in solution (LASiS) is showcased. Dynamic light scattering data and transmission electron microscopy confirm the particle size distribution. UV–vis measurements are performed, and the Beer–Lambert relationship is used to determine the concentration of the generated ink. The inks generated at two different repetition rates are compared: 200 kHz and 1 MHz. X‐Ray diffraction analysis of the aerosol jet printed thin film post‐thermal sintering confirms the grain size and phase purity of the printed thin films. This work demonstrates the effectiveness of the LASiS technique in producing printable nanoparticle inks with little‐to‐no postprocessing.

Aerosol jet printing of surface acoustic wave microfluidic devices

The addition of surface acoustic wave (SAW) technologies to microfluidics has greatly advanced lab-on-a-chip applications due to their unique and powerful attributes, including high-precision manipulation, versatility, integrability, biocompatibility, contactless nature, and rapid actuation. However, the development of SAW microfluidic devices is limited by complex and time-consuming micro/nanofabrication techniques and access to cleanroom facilities for multistep photolithography and vacuum-based processing. To simplify the fabrication of SAW microfluidic devices with customizable dimensions and functions, we utilized the additive manufacturing technique of aerosol jet printing. We successfully fabricated customized SAW microfluidic devices of varying materials, including silver nanowires, graphene, and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). To characterize and compare the acoustic actuation performance of these aerosol jet printed SAW microfluidic devices with their cleanroom-fabricated counterparts, the wave displacements and resonant frequencies of the different fabricated devices were directly measured through scanning laser Doppler vibrometry. Finally, to exhibit the capability of the aerosol jet printed devices for lab-on-a-chip applications, we successfully conducted acoustic streaming and particle concentration experiments. Overall, we demonstrated a novel solution-based, direct-write, single-step, cleanroom-free additive manufacturing technique to rapidly develop SAW microfluidic devices that shows viability for applications in the fields of biology, chemistry, engineering, and medicine.

Revealing The Morphology of Ink and Aerosol Jet Printed Palladium-Silver Alloys Fabricated from Metal Organic Decomposition Inks.

Palladium films hold signicance due to their remarkable affinity for hydrogen diffusion, rendering them valauble for the seperation and purification of hydrogen in membrane reactors. However, palladium is expensive, and its films can become brittle after only a few cycles of hydrogen separation. Alloying with silver has been shown to overcome the problem of palladium embrittlement. Palladium-silver films have been produced via several methods but all have drawbacks, such as difficulties controlling the alloy composition. This study explores two promising jet printing methods: Inkjet and Aerosoljet. Both methods offer potential advantages such as direct patterning, which reduces waste, enables thin film production, and allows for the control of alloy composition. For the first time, palladium-silver alloys have been produced via inkjet printing using a palladium-silver metal organic decomposition (MOD) ink, which alloys at a temperature of 300°C with nitrogen. Similarly, this study also demonstrates a pioneering approach for Aerosol Jet printing, showing the potential of a novel room-temperature method, for the deposition of palladium-silver MOD inks. This low temperature approach is considered an important development as palladium-silver MOD inks are originally designed for deposition on heated substrates.

Aerosol jet printed resistive temperature sensors with high sensitivity

Aerosol jet printing provides a facile, cost-efficient, and environmentally friendly approach to pattern thin films with nanomaterial inks. Printed flexible resistive thin-film temperature sensors play an important role in human body temperature monitoring, soft robotics, prosthetics, and real-time temperature monitoring of large area curved surfaces due to their linear response to temperature, low-cost, scalability, and flexibility. However, the temperature coefficient of the resistance of the printed resistive temperature sensors reported in the literature is much less than that of their bulk metals. In this work, we demonstrate aerosol jet printed resistive temperature sensors with silver nanoparticle ink that have a temperature coefficient of resistance close to that of bulk silver. We report a temperature coefficient of resistance of 3.7 × 10−3 ◦C−1 for the aerosol jet printed resistive temperature sensors, the highest value yet reported in literature for resistive temperature detectors composed of thermally sintered silver nanoparticle thin films. The mechanisms for the increased performance are investigated using metrological and thermal techniques with regard to the source ink and traces. Additionally, we show that the overall sensitivity of the printed sensors can be modulated by controlling the thickness of the printed thin films. Finally, we evaluate the response of the printed resistive sensors to bending strain and humidity, including an investigation into the effects of organic passivation. Overall, this work presents printed sensors with performance on par with vacuum deposited resistive temperature detectors, enabling the fabrication technique to make an industrial impact.

Electrical and Mechanical Behavior of Aerosol Jet–Printed Gold on Alumina Substrate for High‐Temperature Applications

There is a growing interest in the development of microelectronics that can perform reliably and robustly at temperatures above 300 °C. Such devices require stable thermal properties, low thermal drift, and thermal cycling resistance. Conventional hybrid circuit technology demonstrates high‐temperature packages, but the high costs and lead time are significant drawbacks. In contrast, additive manufacturing processes, including aerosol jet printing (AJP), offer cost and time benefits, as well as 3D structures and embedded features. However, the properties and reliability of additive packaging materials at extreme temperatures are not well known. Herein, the reliability at temperatures up to 750 °C in terms of electrical performance and mechanical strength of aerosol jet printed gold thick films onto ceramic substrates are assessed. Thermal coefficient of resistance of printed gold films is measured. The electrical resistance stability and leakage current of printed gold structures are also characterized during over 100 h of aging at temperatures up to 750 °C. Finally, the mechanical adhesion strength of the printed gold films is evaluated after aging for 100 h at temperatures up to 750 °C. The adhesion of the printed gold to the ceramic substrates remains high after aging, very stable resistances and minimal leakage currents have been observed.

Synthesized silver nanoparticles decorated reduced graphene oxide/silver ink for aerosol jet printed conformal temperature sensor with a wide sensing range and excellent stability

Three-dimensional (3D) conformal printing of temperature sensors with a wide sensing range and high stability requires the potential printable material with excellent functionality and printability. Herein, a high-performance silver nanoparticles (Ag NPs) decorated reduced graphene oxide (RGO)/Ag (ADR/Ag) ink with low viscosity was synthesized for aerosol jet printing (AJP). Ag ions are electrostatically adsorbed on the graphene oxide (GO) surface, and Ag NPs (∼10 nm) were attached onto the RGO surface by in-situ liquid-phase reduction. The ADR nanoflakes were mixed with commercial Ag NPs ink, high resolution patterns with ink stream widths down to 10 μm are printed, and ADR/Ag-0.8% ink shows excellent low-temperature sintering capability and flexibility, and the resistivity of the printed traces is 9.79 × 10−5 Ω m after 1 h sintering at a relatively low temperature (75 °C). The resistance negligibly increases by only 5% after 1000 bending cycles, which is about 7 times lower compared to the pure Ag traces. Furthermore, we achieve the 3D printing of a conformal temperature sensor with a sensitivity range of (1.162–1.519) × 10−3/°C in the broad sensing range of 0–200 °C. These findings shed light on the additive manufacturing of high-performance conformal electronics using the emerging AJP technology.

Modeling the effect of bend radius on the performance of a conformal dual-band mm-wave patch antenna array

There is growing interest in the use of additive manufacturing for the fabrication of RF devices due to fast prototyping capabilities and the use of less material as opposed to traditional fabrication techniques. In addition to the previously mentioned advantages, the aerosol jet printing method in particular allows for the conformal printing of RF components. This work models the effect of the bend radius on the return loss and radiation pattern of a dual-band (28 GHz and 39 GHz) mm wave patch antenna array design that will be aerosol jet printed. The antenna is modeled on a 5-mil thick flexible substrate (PET) and the simulation is run from 27 GHz to 40 GHz using HFSS. The return loss and radiation pattern results of the antenna are compared for various bend radii (0.25 in to 2 in) of the conformal surface the antenna is to be printed upon. Simulation results show a maximum frequency deviation of about 400 MHz on the return loss for the low (28 GHz) frequency band of the antenna when it is bent from a bend radius of 0 in to 2 in.

Fully Aerosol Jet-Printed Passive Components for 140–220-GHz Operation

This letter focuses on the unique capabilities that aerosol jet printing (AJP) provides for manufacturing electronics at near-THz frequencies. For the first time, we demonstrate fully aerosol jet-printed passive components above the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$</tex-math> </inline-formula> -band. Dielectric substrates and conductors are printed on metal carriers via AJP. These components include microstrip (MS) transmission lines (TLs) and radial stubs, and utilize vialess grounded coplanar waveguide (GCPW)-to-MS TL launches. Two separate sets of components and calibration structures are realized, for two different dielectric thicknesses. For the TLs, measured from 140 to 220 GHz, the average loss varies from 0.86 to 2.6 dB/mm. The radial stub return loss, measured from 200 to 220 GHz, is closely aligned with simulations.

Design and Fabrication of an Aerosol Jet Printed Tactile Sensor on Flexible Substrate

Inkjet printing for fabricating microstructures has gained popularity during the last decade, making it possible to realize complex electronic circuits, components, and devices previously manufactured using 2D lithographic processes. Aerosol jet printing enables the deposition of feature sizes in the micron-scale order. Investigated in this work, is a tactile sensor featuring a strain gauge in a circular pattern and using aerosol inkjet printing delivered from the NeXus, a custom-built microfabrication platform that can deposit silver ink on a flexible printed circuit (FPC) substrate. Also presented is the finite element analysis (FEA) to evaluate the performance of the tactile sensor, packaged in between cover and bedding created with elastomer to fit the tactile sensor. The elastomer covering and bedding contains a dimple and cavity complying with external deformation, which concentrates the applied indented force. Simulation was used to optimize the configuration of the dimple size, cover, and bedding design required to improve the sensor performance. The fabrication method for creating 10mm diameter circular strain gauge tactile sensors include an annealing process using the oven, developed by comparing different curing time. Finally, experimental indentation tests were carried out under varying curing schedules, evaluated by loading packaged sensors with increasing weight, and indented force profile from 0.5-2.0N. Results show a 67% decrease in resistance from 2-20 hours of oven cure and about a 0.08% increase in sensitivity.

Amperometric Measurements by a Novel Aerosol Jet Printed Flexible Sensor for Wearable Applications

In the last years, increasing interest has been addressed on wearable devices for the continuous monitoring of biochemical profiles of patients and athletes. Among various markers, lactate represents one of the most interesting to deepen the knowledge on fatigue processes, in combination with traditional electromyographic features. In this work, we propose a new, low-cost, rapid, and flexible electrochemical amperometric lactate carbon biosensor fabricated by the novel technique of aerosol jet printing (AJP). The developed biosensors were combined with a paper-based microfluidic system and a chitosan-based stable functionalization to allow a long-term continuous monitoring of human daily activities. The sensor performances were evaluated by static and dynamic electrochemical tests in buffered media. The limit of detection is 11 ± 2 mM for the static setup and of 15 ± 6 mM for the dynamic setup, while sensitivity is 0.02 and 0.04 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{A}$ </tex-math></inline-formula> /mM, respectively, with single sigma standard deviation lower than 8%. Increasing and decreasing concentration steps of lactate induces comparable response times below 30 s. These results obtained in vitro under controlled laboratory conditions represent a promising starting point to pursue with ex-vivo and in vivo validation for the future development of stand-alone wearable patches for noninvasive lactate measurements.

Aerosol Jet Printed Surface-Enhanced Raman Substrates: Application for High-Sensitivity Detection of Perfluoroalkyl Substances.

Printing technologies offer an attractive means for producing low-cost surface-enhanced Raman spectroscopy (SERS) substrates with high-throughput methods. The development of these substrates is especially important for field-deployable detection of environmental contaminants. Toward this end, we demonstrate SERS-based substrates fabricated through aerosol jet printing of silver nanoparticles and graphene inks on Kapton films. Our printed arrays exhibited measurable intensities for fluorescein and rhodamine dyes down to concentrations of 10-7 M, with the highest SERS intensities obtained for four print passes of Ag nanoparticles. The substrates also exhibited an excellent shelf life, with little reduction in fluorescein intensities after 9 months of shelf storage. We also demonstrated the capability of our substrates to sense perfluoroalkyl substances (PFAS), the so-called forever chemicals that resist degradation due to their strong C-F bonds and persist in the environment. Interestingly, the addition of graphene to the Ag nanoparticles greatly enhanced the SERS intensity of the perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) molecules under basic conditions (pH ∼ 9) compared to that of fluorescein and rhodamine. We were able to successfully detect SERS spectra from nano- and picomolar (∼0.4 ppt) concentrations of PFOA and PFOS, respectively, demonstrating the viability of deploying our SERS sensors in the environment for the ultrasensitive detection of contaminants.

Aerosol Jet Printed Organic Memristive Microdevices Based on a Chitosan:PANI Composite Conductive Channel

In this study we show a chitosan:polyaniline (CPA)-based ink, responding to eco-biofriendly criteria, specifically developed for the manufacturing of the first organic memristive device (OMD) with an aerosol jet printed conductive channel. Our contribution is in the context of bioelectronics, where there is an increasing interest in emulating neuromorphic functions. In this framework, memristive devices and systems have been shown to be well suited. In particular organic-based devices are envisaged as very promising in some applications, such as brain–machine interfacing, owing to specific properties of organics (e.g., biocompatibility, mixed ionic–electronic conduction). On the other hand, the research activities on flexible organic (bio)electronic devices and direct writing (DW) noncontact techniques increasingly overlap in the effort of achieving reliable applications benefiting from the rapid prototyping to accomplish a fast device optimization. In this context, ink-based techniques, such as aerosol jet printing (AJP), although particularly well suited to implement 3D-printed electronics due to advantages it offers in terms of a wide set of allowed printable materials, still require research efforts aimed at conferring printability to the desired precursors. The developed CPA composite was characterized by FTIR, DLS, and MALDI-TOF techniques, while the related aerosol jet printed films were studied by SEM and profilometry. Taking advantage of the intrinsic and stable electrical conductivity of CPA films, which do not necessarily require any acidic treatment to promote a sustained charge carrier conduction, 10 μm short-channel OMDs were hence manufactured by interfacing the printed CPA layers with a solid polyelectrolyte (SPE). We accordingly demonstrated prototypes of stable and best performing OMD devices with downscaled features, showing well-defined counterclockwise hysteresis/rectification and an enhanced durability. These properties pave the way to further improving performance, as well as to realizing a direct integration of the devices into hardware neural networks by in-line fabrication routes.

Numerical and experimental investigation of aerosol jet printing

A two-dimensional computational fluid dynamics model is presented to elucidate the fundamental aerodynamic phenomena dictating the morphology of aerosol jet printed features. Under compressible and laminar flow assumptions, governing equations were numerically solved to calculate crucial flow variables at discrete points throughout the fluid domain. Randomized single-factor numerical experiments were performed to unravel the role of volumetric flow rates of sheath gas, carrier gas, flow focusing ratio, overall gas flow rate, and aerosol droplet diameter. A Lagrangian discrete phase model was implemented to predict the trajectories of aerosol streams through the fluid domain at several process conditions. A mathematical model for predicting the width of the aerosol stream at the nozzle exit is also presented. Additionally, polydispersity in the droplet diameter distribution was modeled using the Rosin-Rammler distribution, and the role of the minimum droplet diameter in a polydisperse stream of aerosols in causing overspray is discussed. Overall, the numerical results showed good agreement with experimental measurements from an ultrasonic aerosol jet printing (AJP) system, making the computational framework a valuable tool for optimizing the printing process and for predicting the occurrence of printing defects.

(Digital Presentation) Electrodeposition of Re on Aerosol Jet Printed Metal Seed Layers on Flexible Substrates

Quantum computers (QCs) are expected to run advanced algorithms to solve currently intractable challenges in chemistry simulations, cryptography, medicine, and finance.[1] The Josephson Junction based qubits that power a quantum computer must reside in a cryogenically cooled chamber at 10 mK. Communications with this chip is currently carried out with a chandelier of rigid cables.[2] A flexible cable containing superconducting interconnect lines could in principle simplify the design of QC interconnects and lead to improvement in qubit density and efficiency. We have previously demonstrated the use of aerosol jet printing (AJP) for the patterning of electrodeposited Cu and Ni [3]. We have also recently reported on the development of a water-in-salt method to electrodeposit superconducting Re on evaporated Au on Si substrates. These Re components have a critical temperature above 4.2 K, which makes the superconductivity easily accessible with liquid He cooling[4].We report for the first time the metallization of flexible Kapton substrates with printed Au and Ag nanoparticle inks by aerosol jet printing as the seed for superconductor electrodeposition. Electrodeposition of Re onto the printed structures was performed using the water-in-salt method. ASTM D3359 tests demonstrated that Au has superior adhesion to Kapton, while the Ag seed does not survive rhenium deposition, potentially due to the high internal stress of Re. Further, improved adhesion was demonstrated when Kapton substrates were roughened with 1200 grit sandpaper. Electrodeposited Re on AJP Au seed layer on flexible Kapton substrates, as shown in Figure 1, demonstrated a superconducting transition temperature of 6K. In addition, electrodeposited Re on Au survived 200 cycles of flexure testing under >30 MPa load and 1.2% strain. These efforts demonstrate the proof-of-principle for patterning of superconducting interconnects for the further development of QCs. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2022-11522 A References [1] F. Bova, A. Goldfarb, and R.G. Melko “Commercial Applications of Quantum Computing.” EPJ Quantum Tech. (2021) 8:2.[2] S. Krinner, S. Storz, P. Kurpiers, P. Magnard, J. Heinsoo, R. Keller, J. Lütolf, C. Eichler & A. Wallraff. “Engineering cryogenic setups for 100-qubit scale superconducting circuit systems.” EPJ Quantum Tech. (2019) 6:2.[3] L. K. Tsui, S. C. Kayser, S. A. Strong, and J. M. Lavin, “High Resolution Aerosol Jet Printed Components with Electrodeposition-Enhanced Conductance.” ECS J. Solid State Sci. Tech. (2021). 10, 047001.[4] W. D. Sides, E. Hassani, D. P. Pappas, Y. Hu, T. S. Oh, Q. Huang “Grain growth and superconductivity of rhenium electrodeposited from water-in-salt electrolytes.” J. App. Phys. (2020). 127, 085301.Figure 1. (a) Photograph of a well adhered Re on Au sample. (b) Superconducting transition data for Re on printed Au on Kapton. Figure 1

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.

Aerosol Jet Printed and Photonic Cured Paper-Based Ammonia Sensor for Food Smart Packaging

In this work, we report the manufacturing and experimental analysis of low-cost and eco-friendly paper-based gas sensors for food smart packaging. The hygroscopic properties of paper help detecting the presence of water-soluble gases in an environment provided with relative humidity (RH) above a given threshold (RH > 75%) and discovering the presence of gaseous-markers of the food-spoilage process, like ammonia. Carbon interdigitated electrodes were printed by Aerosol Jet Printing and sintered by Flash Lamp Annealing on chromatographic paper, obtaining a mean resistance value of (231 ± 20) kΩ and (249 ± 28) kΩ for the left and the right electrode, respectively. After being tested at different RH values (75, 80, 90, 100%), and once stabilized, they were tested with different ammonia concentrations (3, 6, 9, and 12 ppm). A proportional resistance decrease was evidenced in increasing ammonia concentration. Considering the baseline at a constant value of RH=75%, the sensors showed a resistance variation of 12% in presence of the lowest concentration of 3 ppm. Three different temperatures were considered during the tests, 5 °C, 15 °C, and 25 °C, evidencing no primary influence of this parameter. Ethanol and acetone were investigated as representatives of interfering compounds such as alcohols and ketones that may be developed during food spoilage. Good selectivity was observed both by studying these compounds individually and together with ammonia. Experimental results showed that 48 ppm of acetone induced a resistance change lower than 3 ppm of ammonia, while 240 ppm of ethanol induced a resistance change comparable to 12 ppm of ammonia.