Aerosol Jet Printed Research Articles

Multi-Physics Modeling and Characterization of Components on Flexible Substrates

Due to the increased popularity of wearable devices, designing flexible hybrid electronics (FHE) is becoming increasingly critical. Some emerging systems that require FHE include wearables, energy-harvesting devices, sensory networks, and electrocardiogram monitors. These systems require designers to account for different flexible actions, such as stretching, bending, twisting, etc. Accounting for different flexible actions requires models for different components that capture the behavior under these actions. This work focuses on characterizing the effects of bending two components, namely, printed microstrip transmission lines and power inductors. In this work, both the mechanical and electrical aspects are captured specifically for aerosol jet-printed (AJP) transmission lines, screen-printed (SP) transmission lines, and SP power inductors on flexible substrates using 3-D finite element modeling (FEM), which are then correlated with the measurements. The challenges in such multi-physics modeling and measurements are discussed, including the effect of bending.

Support-Material-Free Microfluidics on an Electrochemical Sensors Platform by Aerosol Jet Printing.

Printed electronics have led to new possibilities in the detection and quantification of a wide range of molecules important for medical, biotechnological, and environmental fields. The integration with microfluidics is often adopted to avoid hand-deposition of little volumes of reagents and samples on miniaturized electrodes that strongly depend on operator’s skills. Here we report design, fabrication and test of an easy-to-use electrochemical sensor platform with microfluidics entirely realized with Aerosol Jet Printing (AJP). We printed a six-electrochemical-sensors platform with AJP and we explored the possibility to aerosol jet print directly on it a microfluidic structure without any support material. Thus, the sacrificial material removal and/or the assembly with sensors steps are avoided. The repeatability observed when printing both conductive and ultraviolet (UV)-curable polymer inks can be supported from the values of relative standard deviation of maximum 5% for thickness and 9% for line width. We designed the whole microfluidic platform to make the sample deposition (20 μL) independent from the operator. To validate the platform, we quantified glucose at different concentrations using a standard enzyme-mediated procedure. Both mediator and enzyme were directly aerosol jet printed on working electrodes (WEs), thus the proposed platform is entirely fabricated by AJP and ready to use. The chronoamperometric tests show limit of detection (LOD) = 2.4 mM and sensitivity = 2.2 ± 0.08 µA/mM confirming the effectiveness of mediator and enzyme directly aerosol jet printed to provide sensing in a clinically relevant range (3–10 mM). The average relative standard inter-platform deviation is about 8%. AJP technique can be used for fabricating a ready-to-use microfluidic device that does not need further processing after fabrication, but is promptly available for electrochemical sample analysis.

High Capacity Rate Capable Aerosol Jet Printed Li‐Ion Battery Cathode

A thick (170 μm) LiFePO4 cathode is fabricated through aerosol jet printing. The printed cathode displays a pattern of aligned high aspect ratio needles which, in cross section, produce micron scale channels. These channels surround regions of LiFePO4 that possess submicron pores. When tested in half cell configuration versus a Li‐foil anode, the specific discharge capacity of the printed cathode is 151 mAh g−1 at a C/15 rate and 105 mAh g−1 at 1C. These values correspond to area normalized discharge capacities of 2.5 and 1.7 mAh cm−2 at current densities of 0.2 and 2.4 mA cm−2, respectively. In a 50 cycle constant current charge/discharge test, the discharge capacity is stable, retaining 89% of its initial C/5 capacity. These results suggest that aerosol jet deposition is a promising printing technique for fabricating high capacity, rate capable, Li‐ion battery cathodes.

Photonic curing of silver paths on 3D printed polymer substrate

Purpose Despite almost limitless possibilities of rapid prototyping, the idea of 3D printed fully functional electronic device still has not been fulfilled – the missing point is a highly conductive material suitable for this technique. The purpose of this paper is to present the usage of the photonic curing process for sintering highly conductive paths printed on the polymer substrate. Design/methodology/approach This paper evaluates two photonic curing processes for the conductive network formulation during the additive manufacturing process. Along with the xenon flash sintering for aerosol jet-printed paths, this paper examines rapid infrared sintering for thick-film and direct write techniques. Findings This paper proves that the combination of fused deposition modeling, aerosol jet printing or paste deposition, along with photonic sintering, is suitable to obtain elements with low resistivity of 3,75·10−8 Ωm. Presented outcomes suggest the solution for fabrication of the structural electronics systems for daily-use applications. Originality/value The combination of fused deposition modelling (FDM) and aerosol jet printing or paste deposition used with photonic sintering process can fill the missing point for highly conductive materials for structural electronics.

Aerosol-Jet Printed Interconnects for 60-Gb/s CMOS Driver and Microring Modulator Transmitter Assembly

We developed an aerosol-jet printing technique to realize an optical transmitter assembly of a microring modulator and a high-speed CMOS driver in which the bonding wires are replaced by aerosol-jet printed silver interconnects. First, the technology is characterized by printing coplanar waveguides (CPWs) test structures on glass and epoxy in order to fully investigate the electro-magnetic behavior of the aerosol-jet printed interconnects. The printed CPWs on glass and epoxy showed a low attenuation of 0.57 and 0.76 dB/mm at 50 GHz, respectively. Then, the aerosol-jet printed interconnects were benchmarked with conventional bonding wires while separately interconnecting the ring modulator without the CMOS driver. The measured reflection coefficient ( $S_{11}$ ) of the aerosol-jet printed interconnects showed an increase in a resonance frequency of 20 GHz compared with Al bonding wires. Furthermore, the optical transmitter was successfully demonstrated at 60 Gb/s and the measured optical eye diagrams were clearly open even after 2 km of standard single-mode fiber. An extinction ratio of 4.63 dB was achieved while applying a drive voltage of 1 $\text{V}_{\mathrm{ pp}}$ .

Aerosol-Printed Highly Conductive Ag Transmission Lines for Flexible Electronic Devices

We studied aerosol jet printing on flexible substrates for wearable and flexible electronic devices. First, we investigated the electrical conductivity of aerosol jet printed silver layers at different temperatures. An electrical conductivity up to 60% of bulk Ag was measured after sintering at 140 °C on a hot plate. Higher conductivities became possible with higher sinter temperatures. The printed ink showed a surprisingly high flexibility. Transmission lines were printed on flexible substrates [Kapton and Rogers liquid crystal polymer (LCP) foils], and the performance was measured up to 110 GHz. The coplanar waveguide transmission lines demonstrated insertion losses of 0.366 dB/mm for LCP and 0.546 dB/mm for Kapton foils at 110 GHz.

Fully Aerosol-Jet Printed, High-Performance Nanoporous ZnO Ultraviolet Photodetectors

We report fully aerosol-jet printed ultraviolet photodetectors based on zinc oxide nanocrystal networks having a porous morphology. The developed photodetectors exhibit selective optical photoresponse in the ultraviolet spectrum at wavelengths ranging from 250 nm up to 400 nm. These devices show a high ON/OFF ratio of ∼106 and short response times. The characteristic time constants for the rise and fall edges were measured to be ∼0.4 and ∼1.3 s, respectively. In this work, we propose a direct approach for aerosol-jet printing of presynthesized nanocrystals to overcome the limitations of high post-annealing temperatures and tedious fabrication methods to obtain high aspect ratio nanostructures. The high performance characteristics of these devices are attributed to Schottky barrier modification under the influence of oxygen, which is enhanced by the porosity of the semiconductor material. The random orientation of the crystals aids the formation of air traps in the network, thereby enhancing the surface ar...

Enhanced thermoelectric properties of flexible aerosol-jet printed carbon nanotube-based nanocomposites

Aerosol-jet printing allows functional materials to be printed from inks with a wide range of viscosities and constituent particle sizes onto various substrates, including the printing of organic thermoelectric materials on flexible substrates for low-grade thermal energy harvesting. However, these materials typically suffer from relatively poor thermoelectric performance, compared to traditional inorganic counterparts, due to their low Seebeck coefficient, S, and electrical conductivity, σ. Here, we demonstrate a modified aerosol-jet printing technique that can simultaneously incorporate well-dispersed high-S Sb2Te3 nanoflakes and high-σ multi-walled carbon nanotubes (MWCNTs) providing good inter-particle connectivity to significantly enhance the thermoelectric performance of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate structures on flexible polyimide substrates. A nominal loading fraction of 85 wt. % yielded a power factor of ∼41 μW/mK2, which is among the highest for printed organic-based structures. Rigorous flexing and fatigue tests were performed to confirm the robustness and stability of these aerosol-jet printed MWCNT-based thermoelectric nanocomposites.

Electrical Transport and Power Dissipation in Aerosol-Jet-Printed Graphene Interconnects

This paper reports the first known investigation of power dissipation and electrical breakdown in aerosol-jet-printed (AJP) graphene interconnects. The electrical performance of aerosol-jet printed (AJP) graphene was characterized using the Transmission Line Method (TLM). The electrical resistance decreased with increasing printing pass number (n); the lowest sheet resistance measured was 1.5 kΩ/sq. for n = 50. The role of thermal resistance (RTH) in power dissipation was studied using a combination of electrical breakdown thermometry and infrared (IR) imaging. A simple lumped thermal model ({boldsymbol{Delta }}{bf{T}}={bf{P}}{boldsymbol{times }}{{bf{R}}}_{{bf{TH}}}) and COMSOL Multiphysics was used to extract the total RTH, including interfaces. The RTH of AJP graphene on Kapton is ~27 times greater than that of AJP graphene on Al2O3 with a corresponding breakdown current density 10 times less on Kapton versus Al2O3.

Aerosol jet printed silver nanowire transparent electrode for flexible electronic application

Aerosol jet printing technology enables fine feature deposition of electronic materials onto low-temperature, non-planar substrates without masks. In this work, silver nanowires (AgNWs) are proposed to be printed into transparent flexible electrodes using a Maskless Mesoscale Material Deposition Aerosol Jet® printing system on a glass substrate. The influence of the most significant process parameters, including printing cycles, printing speed, and nozzle size, on the performance of AgNW electrodes was systematically studied. The morphologies of printed patterns were characterized by scanning electron microscopy, and the transmittance was evaluated using an ultraviolet-visible spectrophotometer. Under optimum conditions, high transparent AgNW electrodes with a sheet resistance of 57.68 Ω/sq and a linewidth of 50.9 μm were obtained, which is an important step towards a higher performance goal for flexible electronic applications.

In-Place Printing of Carbon Nanotube Transistors at Low Temperature

Interest in flexible, stretchable, and wearable electronics has motivated the development of additive printing to fabricate customizable devices and systems directly onto virtually any surface. However, progress has been limited by the relatively high temperatures (>200 °C) required to sinter metallic inks and time-consuming process steps, many of which require removal of the substrate from the printer for coating, washing, or sintering. In this work, we addressed these challenges and demonstrate carbon nanotube thin-film transistors (CNT-TFTs) that are fabricated by aerosol jet printing with the substrate never leaving the printer. The full in-place printing approach, from first step to last, used a maximum process temperature of only 80 °C on the printer platen. Silver nanowire (Ag NW) ink was found to be most viable for low-temperature, in-place sintering while still yielding good electrical interfaces to the CNT thin-film channels. These aerosol-jet printed Ag NW films were conductive immediately afte...

Aerosol Jet Printed Strain Sensor: Simulation Studies Analyzing the Effect of Dimension and Design on Performance (September 2018)

The 3-D printing has been gaining widespread attention for electronic applications. Aerosol jet printing has emerged as a powerful technique to print new-age sensors and devices on various substrates. In this paper, we use simulation studies to optimize the dimensions and design of aerosol jet printed strain sensor for a good performance. Physical dimensions such as the end loop length, number of grids, grid line width, gauge length, and five different sensor designs are simulated to study their effect on the performance of the strain sensor. This paper helps to identify the factors that affect the sensitivity and gauge factor of the flexible strain sensor fabricated using aerosol jet printing technology.

Controlling and assessing the quality of aerosol jet printed features for large area and flexible electronics

Aerosol jet printing (AJP) is a versatile technique suitable for large-area, fine-feature patterning of both rigid and flexible substrates with a variety of functional inks. In particular, AJP can tolerate ink viscosities between 1 and 1000 cP, with printing resolution of the order of 10 μm, thus making it attractive for flexible and printed electronics. This work investigates in detail significant aspects of ink-substrate combination and substrate temperature that are highly relevant to AJP. In order to do this, thin conducting silver lines are printed using AJP on both rigid (glass and silicon) as well as flexible (polyimide) substrates. The correlation between the various deposition parameters and the ‘quality’ of the printed lines are evaluated, through measurements of electrical conductivity under different experimental conditions. Based on our findings, a framework is proposed through which the morphology of AJP lines can be controlled and assessed for applications in large area and flexible electronic devices.

Aerosol-Jet printing of highly flexible and conductive graphene/silver patterns

This article addresses the development of a graphene/silver nanoparticle (Ag NP) ink and its deployment in an aerosol-jet additive manufacturing system in order to print highly conductive and flexible graphene/Ag patterns for flexible printed electronics. Printing with graphene/Ag NP ink produced a uniform microstructure and crack-free printed patterns. With a mean resistivity of 1.07×10−4Ωcm, these graphene/Ag NP patterns have about 100 times less resistivity compared to graphene patterns and three times less resistivity than Ag NP patterns, made with the same printing system. With their low degree of resistivity and the same flexibility as the graphene printed patterns, resulted from the bending test, graphene/Ag aerosol-jet printed patterns may therefore be considered as an efficient candidate compared to either graphene or Ag NP printed patterns for flexible electronics.

(Invited) Vlsi Carbon Nanotube Thin-Film Circuits

With the availability of large quantities of electronically monodisperse carbon nanotubes (CNTs) [1], homogeneous semiconducting CNT thin films can be produced through a variety of solution-based methods including vacuum filtration [2], dielectrophoresis [3], evaporation-driven self-assembly [4], aerosol jet printing [5], and inkjet printing [6,7]. Through careful integration of these thin films with high-k gate dielectrics [8], CNT thin-film transistors (TFTs) can achieve device metrics that are competitive with polycrystalline silicon and amorphous oxide semiconductors [9]. Furthermore, with appropriate device geometries, doping schemes, and gate electrode materials, threshold voltage can be tuned to enable enhancement-mode p-type and n-type TFTs, resulting in CNT CMOS logic gates with subnanowatt static power dissipation and full rail-to-rail voltage swing [10]. While these results suggest that very-large-scale integration (VLSI) should be possible for CNT thin-film circuits, further improvements are needed in CNT TFT large-area spatial homogeneity and long-term environmental stability. Towards these ends, this talk will introduce encapsulation schemes and automated measurement strategies that yield wafer-scale CNT TFT arrays with sufficiently tight control over on/off ratio, subthreshold swing, and threshold voltage for VLSI CNT thin-film circuits. Using this methodology, large-area arrays of fully functional CNT TFT static random access memory (SRAM) cells are demonstrated with desirable static noise and write margins. [1] D. Jariwala, V. K. Sangwan, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Carbon nanomaterials for electronics, optoelectronics, photovoltaics, and sensing,” Chem. Soc. Rev., 42, 2824 (2013). [2] A. Behnam, V. K. Sangwan, X. Zhong, F. Lian, D. Estrada, D. Jariwala, A. J. Hoag, L. J. Lauhon, T. J. Marks, M. C. Hersam, and E. Pop, “High-field transport and thermal reliability of sorted carbon nanotube network devices,” ACS Nano, 7, 482 (2013). [3] M. Steiner, M. Engel, Y.-M. Lin, Y. Wu, K. Jenkins, D. B. Farmer, J. J. Humes, N. L. Yoder, J.-W. T. Seo, A. A. Green, M. C. Hersam, R. Krupke, and Ph. Avouris, “High-frequency performance of scaled carbon nanotube array field-effect transistors,” Appl. Phys. Lett., 101, 053123 (2012). [4] T. A. Shastry, J.-W. T. Seo, J. J. Lopez, H. N. Arnold, J. Z. Kelter, V. K. Sangwan, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Large-area, electronically monodisperse, aligned single-walled carbon nanotube thin films fabricated by evaporation-driven self-assembly,” Small, 9, 45 (2013). [5] M. Ha, J.-W. T. Seo, P. L. Prabhumirashi, W. Zhang, M. L. Geier, M. J. Renn, C. H. Kim, M. C. Hersam, and C. D. Frisbie, “Aerosol jet printed, low voltage, electrolyte-gated carbon nanotube ring oscillators with sub-5 µs stage delays,” Nano Lett., 13, 954 (2013). [6] B. Kim, S. Jang, M. L. Geier, P. L. Prabhumirashi, M. C. Hersam, and A. Dodabalapur, “High-speed, inkjet-printed carbon nanotube/zinc tin oxide hybrid complementary ring oscillators,” Nano Lett., 14, 3683 (2014). [7] B. Kim, S. Jang, M. L. Geier, P. L. Prabhumirashi, M. C. Hersam, and A. Dodabalapur, “Inkjet printed ambipolar transistors and inverters based on carbon nanotube/zinc tin oxide heterostructures,” Appl. Phys. Lett., 104, 062101 (2014). [8] Y.-G. Ha, K. Everaerts, M. C. Hersam, and T. J. Marks, “Hybrid gate dielectric materials for unconventional electronic circuitry,” Acc. Chem. Res., 47, 1019 (2014). [9] V. K. Sangwan, R. P. Ortiz, J. M. P. Alaboson, J. D. Emery, M. J. Bedzyk, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Fundamental performance limits of carbon nanotube thin-film transistors achieved using hybrid molecular dielectrics,” ACS Nano, 6, 7480 (2012). [10] M. L. Geier, P. L. Prabhumirashi, J. J. McMorrow, W. Xu, J.-W. T. Seo, K. Everaerts, C. H. Kim, T. J. Marks, and M. C. Hersam, “Subnanowatt carbon nanotube complementary logic enabled by threshold voltage control,” Nano Lett., 13, 4810 (2013).

Aerosol jet printed p- and n-type electrolyte-gated transistors with a variety of electrode materials: exploring practical routes to printed electronics.

Printing electrically functional liquid inks is a promising approach for achieving low-cost, large-area, additive manufacturing of flexible electronic circuits. To print thin-film transistors, a basic building block of thin-film electronics, it is important to have several options for printable electrode materials that exhibit high conductivity, high stability, and low-cost. Here we report completely aerosol jet printed (AJP) p- and n-type electrolyte-gated transistors (EGTs) using a variety of different electrode materials including highly conductive metal nanoparticles (Ag), conducting polymers (polystyrenesulfonate doped poly(3,4-ethylendedioxythiophene, PEDOT:PSS), transparent conducting oxides (indium tin oxide), and carbon-based materials (reduced graphene oxide). Using these source-drain electrode materials and a PEDOT:PSS/ion gel gate stack, we demonstrated all-printed p- and n-type EGTs in combination with poly(3-hexythiophene) and ZnO semiconductors. All transistor components (including electrodes, semiconductors, and gate insulators) were printed by AJP. Both kinds of devices showed typical p- and n-type transistor characteristics, and exhibited both low-threshold voltages (<2 V) and high hole and electron mobilities. Our assessment suggests Ag electrodes may be the best option in terms of overall performance for both types of EGTs.

Oxygen Reduction Reaction Activity of Aerosol Jet Printed Layers of Graphite and Graphene

Graphene and graphene-based materials have shown great promise in a broad range of applications including electrochemical sensors, supercapacitors, and lithium ion batteries. However, practical realization of the potential utility of graphene requires development of low cost, high volume methods of material synthesis and manufacturing-ready methods of device fabrication. This work aims to address the second challenge by demonstrating the use of aerosol jet printing for the fabrication of catalytically active electrodes.Graphene and graphite were formulated into high concentration inks (10mg/mL). These inks were aerosol jet printed to create micron scale layers (2 – 10 microns). The catalytic activity of the aerosol jet printed electrodes was evaluated in oxygen saturated basic solution. It was found that the oxygen reduction reaction activity of the aerosol jet printed graphene electrode was ~ 5 times higher times than the activity of the same material when drop cast. Electrochemical impedance spectroscopy showed that the activity difference correlated with a large decrease in the charge transfer resistance of aerosol jet printed graphene as opposed to drop cast graphene. Further, the activity of the aerosol jet printed graphene electrode was ~ 3 times greater than the activity of the aerosol jet printed graphite. In contrast, the drop cast materials did not show a measurable difference in performance. These results indicate that aerosol jet printing is a viable way to deposit micron scale layers of graphene and related materials. In addition, the activity of the graphene electrode is strongly dependent on the deposition method, with aerosol jet deposited electrodes showing a strong performance improvement over their drop cast counterparts.

Non-contact printed aluminum for metallization of Si photovoltaics

Aerosol jet printing is a contactless deposition technique that is ideally suited to depositing features on very thin and fragile substrates such as Si wafers. It can also be used to optimize device geometries including the Al back contact of a Si wafer solar cell quickly. A printable Al ink is required for this process, and we report lines and solar cells prepared with such a material. The resistivities of the printed Al lines approach bulk after appropriate sintering. Al lines printed on Si wafers have been heated over a wide temperature range of 550 to 800°C to form low resistance contacts suitable for current extraction. Aerosol jet printed Al contacts to industrially produced 21cm2 polycrystalline Si solar cells performed on par with all screen printed contacts on similar cells. These promising results demonstrate the potential for non-contact printed Al to contribute to the fabrication of low-cost photovoltaic devices and modules.

Fabrication and characterization of aerosol-jet printed strain sensors for multifunctional composite structures

Traditional multifunctional composite structures are produced by embedding parasitic parts, such as foil sensors, optical fibers and bulky connectors. As a result, the mechanical properties of the composites, especially the interlaminar shear strength (ILSS), could be largely undermined. In the present study, we demonstrated an innovative aerosol-jet printing technology for printing electronics inside composite structures without degrading the mechanical properties. Using the maskless fine feature deposition (below 10 μm) characteristics of this printing technology and a pre-cure protocol, strain sensors were successfully printed onto carbon fiber prepregs to enable fabricating composites with intrinsic sensing capabilities. The degree of pre-cure of the carbon fiber prepreg on which strain sensors were printed was demonstrated to be critical. Without pre-curing, the printed strain sensors were unable to remain intact due to the resin flow during curing. The resin flow-induced sensor deformation can be overcome by introducing 10% degree of cure of the prepreg. In this condition, the fabricated composites with printed strain sensors showed almost no mechanical degradation (short beam shearing ILSS) as compared to the control samples. Also, the failure modes examined by optical microscopy showed no difference. The resistance change of the printed strain sensors in the composite structures were measured under a cyclic loading and proved to be a reliable mean strain gauge factor of 2.2 ± 0.06, which is comparable to commercial foil metal strain gauge.

Aerosol jet printed grid for ITO-free inverted organic solar cells

Aerosol jet printing is investigated as a new deposition method for a current collecting grid in indium tin oxide (ITO) free organic solar cells with an inverted layer sequence. In this device configuration, the ITO layer which usually serves as the hole contact is replaced by a transparent highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer in combination with a silver grid deposited by aerosol jet printing. Since the cells are illuminated from the grid side, the optimisation of the grid design is a trade-off between area coverage and conductivity of the grid lines. These factors have been controlled by the printing parameters such as chuck temperature, printing speed and the number of printing passes. In this paper, we demonstrate that continuous, conductive grid lines with a minimum line width of 58μm can be processed on the top of the PEDOT:PSS layer. For single pass printing the area coverage varied from 5.8% to 11.9% with corresponding effective sheet resistances ranging from 8.9Ω to 1.5Ω. The ITO-free inverted devices with aerosol jet printed grid (an active area of 1.1cm2) show comparable performance to the cells with an evaporated gold grid. The effective sheet resistance can be further decreased by multiple printing passes without increasing the area coverage proportionally due to an improved aspect ratio. By increasing the conductivity and aspect ratio by multiple line printing, the cell length in the module structures can be significantly extended.