Research

Printed hybrid electronics and aerosol jet printing

Our research is focused on additive manufacturing technologies for electronic materials. We specifically focus on a digital printing method called aerosol jet printing, which deposits micron-scale droplets of functional liquid inks to produce fine (~20-50 micron) patterns. This can be used to fabricate electronic devices (e.g., sensors, antennas), print wiring to manufacture more complex circuits include conventional microelectronics and passive electronic devices, and target more advanced structures including high aspect ratio pattern and composition gradients. Our work in aerosol jet printing (AJP) spans efforts to understand the physics of the printing process, and thus more rationally approach ink formulation and modification of the printing system; improve manufacturing reliability through unique process monitoring and control technologies; fabricate electronics on curved 3D surfaces by exploiting the high nozzle-surface offset during printing and digital motion planning; and develop new materials, including gradient patterning with multiple materials. Additional details related to each of these four core topics is included below.

Aerosol jet printing process fundamentals

We aim to establish a holistic framework to understand the physics of AJP, which can provide guidance for material development, process parameter optimization, and printing system design. This provides a versatile foundation for other research efforts, and is based on tailored experiments, computational modeling, and theory-driven analysis.

(a) Schematic of aerosol jet printing, showing droplet atomization, transport, collimation, aerodynamic focusing, and impaction processes. Key process parameters of flow rates and atomizer power are identified, along with metrics including deposition rate and resolution. (b) Numerical modeling of droplet evaporation within the printhead; the plot shows the droplet radius as the color scale in an axisymmetric view within the printhead. (c) Quantitative estimate of impaction efficiency derived from process science experiments, showing that at low deposition rates the impaction efficiency is very low, but it increases asymptotically towards unity at high deposition rates. (d) Demonstration of drying control to improve overspray in the ‘wet’ condition. In the 'dry' condition, there is significant overspray around the main printed line, but this effect is mitigated in the 'wet' condition by suppressing droplet evaporation. — (a) Schematic of aerosol jet printing, highlighting primary process parameters and metrics. (b) Numerical modeling of droplet evaporation within the printhead. (c) Quantitative estimate of impaction efficiency derived from process science experiments. (d) Demonstration of drying control to improve overspray in the ‘wet’ condition.

Representative publications:

[54] Guyll, B.I.; Sanford, B.L.; Pint, C.L.; Secor, E.B. Controlling Droplet Evaporation in Aerosol Jet Printing to Understand and Mitigate Overspray. Small Science 2025, 2500069. https://doi.org/10.1002/smsc.202500069

[51] Guyll B.I.; Petersen L.D.; Pint C.L.; Secor E.B. Enhanced Resolution, Throughput, and Stability of Aerosol Jet Printing via In Line Heating. Adv. Funct. Mater. 2024, 2316426. https://doi.org/10.1002/adfm.202316426

[36] Tafoya, R.R.; Secor, E.B. Understanding Effects of Printhead Geometry in Aerosol Jet Printing. Flex. Print. Electron., 2020, 5, 035004. https://doi.org/10.1088/2058-8585/aba2bb

[33] Tafoya, R.R.; Secor, E.B. Understanding and Mitigating Process Drift in Aerosol Jet Printing. Flex. Print. Electron., 2020, 5, 015009. https://doi.org/10.1088/2058-8585/ab6e74

[28] Secor E.B. Guided Ink and Process Design for Aerosol Jet Printing Based on Annular Drying Effects. Flex. Print. Electron. 2018, 3(3):035007. https://doi.org/10.1088/2058-8585/aadffd

[26] Secor E.B. Principles of Aerosol Jet Printing. Flex. Print. Electron. 2018, 3(3):035002. https://doi.org/10.1088/2058-8585/aace28

Process monitoring and control for aerosol jet printing

Process reliability is a key requirement for practical applications of AJP. We have developed an in-line process monitoring technology based on light scattering to estimate the deposition rate in real time during printing. By integrating this measurement with the printer control software, we have demonstrated closed loop control during printing to mitigate long-term process drift. Moreover, correlating this measurement with the spatial position of the printer allows a rudimentary simulation of the printed part for quality monitoring. Finally, this measurement provides critical insight on mechanisms happening within the printhead, thus providing a unique tool to advance fundamental process studies.

(a) Schematic of light scattering measurements for real-time process monitoring during printing. The aerosol travels through an optics cell upstream of the printer, and light scattered off the aerosol stream in this optics cell is measured. (b) Demonstration of print simulation based on actual process data, mapping the expected thickness spatially within a printed pattern. Here a serpentine pattern was printed with a defect, and the light scattering data shows where the defect is expected based on the real-time data. (c, d) Demonstrations of closed-loop control for aerosol jet printing via automated modulation of the printing conditions to maintain a stable print output. The first demonstration is a 12 hour print in which the atomizer gas flow rate was atomically adjusted to maintain fairly stable cross sectional area. The second demonstration is a 3 hour print with very consistent electrical conductance for printed samples. — (a) Schematic of light scattering measurements for real-time process monitoring during printing. (b) Demonstration of print simulation based on actual process data, mapping the expected thickness spatially within a printed pattern. (c, d) Demonstrations of closed-loop control for aerosol jet printing via automated modulation of the printing conditions to maintain a stable print output.

Representative publications:

[58] Schwartz, A.J.; Rurup, J.D.; Secor, E.B. Multiparameter Closed-Loop Control to Advance Reliability of Aerosol Jet Printing. Adv. Mater. Technol. Just Accepted.

[57] Rurup, J.D.; Bui, D.; Secor, E.B. Deconvoluting Sources of Variability in Aerosol Jet Printing using Light Scattering Measurements. Flexible and Printed Electronics 2025, 10:035013. https://doi.org/10.1088/2058-8585/ae0049

[56] Schwartz, A.J.; Rurup, J.D.; Secor, E.B. Closing the loop on pneumatic atomization for shift-length aerosol jet printing with real-time light scattering measurements. J. Manuf. Process. 2025, 152:631-637. https://doi.org/10.1016/j.jmapro.2025.08.023

[50] Rurup J.D.; Secor E.B. In-Situ Qualification and Physics-Based Process Design for Aerosol Jet Printing via Spatially Correlated Light Scattering Measurements. Addit. Manuf. 2024, 82:104037. https://doi.org/10.1016/j.addma.2024.104037

[48] Rurup J.D.; Secor E.B. A Real-Time Process Diagnostic to Support Reliability, Control, and Fundamental Understanding in Aerosol Jet Printing. Adv. Eng. Mater. 2023, 2301348. https://doi.org/10.1002/adem.202301348.

[44] Rurup J.D.; Secor E.B. Predicting Deposition Rate and Closing the Loop on Aerosol Jet Printing with In‐Line Light Scattering Measurements. Adv. Eng. Mater. 2023, 2201919. https://doi.org/10.1002/adem.202201919.

[41] Secor E.B. Light Scattering Measurements to Support Real-Time Monitoring and Closed-Loop Control of Aerosol Jet Printing. Additive Manufacturing 2021, 44:102028. https://doi.org/10.1016/j.addma.2021.102028

[38] Tafoya R.R.; Cook A.W.; Kaehr B.; Downing J.R.; Hersam M.C.; Secor E.B. Real-Time Optical Process Monitoring for Structure and Property Control of Aerosol Jet Printed Functional Materials. Adv. Mater. Technol. 2020, 5(12):2000781. https://doi.org/10.1002/admt.202000781

Conformal printed electronics

A key opportunity for aerosol jet printing, afforded by its tolerant nozzle-surface standoff distance (~1-5 mm), is the ability print on nonplanar surfaces. While a powerful capability in principle, this introduces greater complexity for motion planning and alignment. We have developed a printing system mounted on an articulated robotic arm to address printing challenges for large-area, low-curvature surfaces, with additional utility for some constrained geometries. This effort includes hardware and method development, fundamental studies of aerosol transport and deposition unique to this configuration, and computational approaches to streamline motion planning.

(a) Aerosol jet printing system based on an articulated robot arm. The aerosol jet printhead is mounted onto the end of a six-axis compact robot arm, and is printing on a vertical surface and on a rounded cube. (b) Toolpath wrapping functionality to conform complex patterns onto curved surfaces. A patch antenna geometry is shown with the 2D antenna geometry and a 3D surface with a saddle geometry, and then the wrapping algorithm places the specific toolpaths onto the curved 3D surface. (c) Computational model of the aerosol jet in an oblique configuration. Here the magnitude of jet velocity is shown when printing onto a tilted substrate, highlighting the asymmetry in the jet that can lead to deviations from a standard, surface normal printing configuration. — (a) Aerosol jet printing system based on an articulated robot arm. (b) Toolpath wrapping functionality to conform complex patterns onto curved surfaces. (c) Computational model of the aerosol jet in an oblique configuration.

Representative publications:

[53] Rurup J.D.; Secor E.B.. Understanding Oblique Deposition in Aerosol Jet Printing for Conformal Electronics Fabrication. J. Manuf. Process. 2024, 120:1231-1240. https://doi.org/10.1016/j.jmapro.2024.05.004

[52] Jignasu A.; Rurup J.D.; Secor E.B.; Krishnamurthy A. NURBS-Based Path Planning for Aerosol Jet Printing of Conformal Electronics. J. Manuf. Process. 2024, 118:187–194. https://doi.org/10.1016/j.mfglet.2023.08.011

Materials development and multimaterial printing

Formulating inks for aerosol jet printing will enable new applications for printed circuits, sensors, and other devices. The fabrication capabilities, along with constraints on ink formulation, are compounded during multimaterial printing with in-line mixing, which has been demonstrated for combinatorial printing, gradient material fabrication, and in situ mixing of reactive components.

(a, b) Aerosol jet printing graphene micropillars with high aspect ratio, achieved by tailoring the ink formulation to effect rapid change in rheology during printing (scale bar 100 µm). The figure in (a) contains a series of SEM images showing graphene micropillars, while the figure in (b) is optical profilometry data showing a height map across a ~4x4 mm area with an array of micropillars that have varying heights. (c) Gradient in conductivity across a multimaterial printed film containing graphene and carbon nano onions with a varying ratio (scale bar 5 mm). The plot shows the conductivity plotting against position in the film, showing a gradual transition over 2 orders of magnitude in the material conductivity by changing the graphene and carbon nano onions ratio. The inset image is a photograph of the sample, showing a visible change in color from dark to light gray corresponding to the change from carbon nano onions to graphene. — (a, b) Aerosol jet printing graphene micropillars with high aspect ratio, achieved by tailoring the ink formulation to effect rapid change in rheology during printing (scale bar 100 µm). (c) Gradient in conductivity across a multimaterial printed film containing graphene and carbon nano onions with a varying ratio (scale bar 5 mm).

Representative publications:

[49] Gamba, L.; Razzaq, M.E.A.; Diaz-Arauzo S.; Hersam M.C.; Bai, X.; Secor E.B. Tailoring Electrical Properties in Carbon Nanomaterial Patterns with Multi-Material Aerosol Jet Printing. ACS Appl. Mater. Interfaces 2023, https://doi.org/10.1021/acsami.3c15088

[47] Gamba, L.; Diaz-Arauzo S.; Hersam M.C.; Secor E.B.Aerosol Jet Printing of Phase Inversion Graphene Inks for High Aspect Ratio Printed Electronics and Sensors. ACS Appl. Nano Mater. 2023, acsanm.3c04207. https://doi.org/10.1021/acsanm.3c04207

[45] Gamba, L.; Lajoie, J.A.; Sippel, T.R.; Secor E.B.Multi-Material Aerosol Jet Printing of Al/CuO Nanothermites for Versatile Fabrication of Energetic Antennas. Adv. Funct. Mater. 2023, 2304060. https://doi.org/10.1002/adfm.202304060

[43] Gamba L.; Johnson Z.T.; Atterberg J.; Diaz-Arauzo S.; Downing J.R.; Claussen J.C.; Hersam M.C.; Secor E.B. Systematic Design of a Graphene Ink Formulation for Aerosol Jet Printing. ACS Appl. Mater. Interfaces 2023, 15(2):3325–3335. https://doi.org/10.1021/acsami.2c18838