Approaching the Practical Conductivity Limits of Aerosol Jet Printed Silver

Abstract

Previous efforts to directly write conductive metals have been narrowly focused on nanoparticle ink suspensions that require aggressive sintering (>200°C) and result in low-density, small-grained agglomerates with electrical conductivities <25% of bulk metal. Here, we demonstrate aerosol jet printing of a reactive ink solution and characterize high-density (93%) printed silver traces having near-bulk conductivity and grain sizes greater than the electron mean free path, while only requiring a lowtemperature (80°C) treatment. We have developed a predictive electronic transport model which correlates the microstructure to the measured conductivity and identifies a strategy to approach the practical conductivity limit for printed metals. Our analysis of how grain boundaries and tortuosity contribute to electrical resistivity provides insight into the basic materials science that governs how an ink formulator or process developer might approach improving the conductivity. Transmission line measurements validate that electrical properties are preserved up to 20 GHz, which demonstrates the utility of this technique for printed RF components. This work reveals a new method of producing robust printed electronics that retain the advantages of rapid prototyping and three-dimensional fabrication while achieving the performance necessary for success within the aerospace and communications industries.

Real‐Time Optical Process Monitoring for Structure and Property Control of Aerosol Jet Printed Functional Materials

“…[ 5,6 ] AJP uses a focused aerosol stream of a liquid ink to deposit high resolution (10–50 µm), thin film (typically <10 µm) patterns of functional materials such as conductive nanoparticles and dielectric polymers. [ 7 ] Due to its programmable, non‐contact, and versatile nature, AJP has been utilized for a wide range of electronic device applications, including logic circuits, [ 8,9 ] sensing, [ 10,11 ] energy conversion, [ 12,13 ] wireless communication, [ 14,15 ] and energy storage. [ 16 ] However, widespread adoption of AJP in industrial manufacturing is uncommon due to its poor process consistency.…”

“…DOI: 10.1002/admt.202000781 and dielectric polymers. [7] Due to its programmable, non-contact, and versatile nature, AJP has been utilized for a wide range of electronic device applications, including logic circuits, [8,9] sensing, [10,11] energy conversion, [12,13] wireless communication, [14,15] and energy storage. [16] However, widespread adoption of AJP in industrial manu facturing is uncommon due to its poor process consistency.…”

Highly conductive electronics circuits from aerosol jet printed silver inks

“…The result values calculated for D2 sample ink—resistivity 4.5·10 −8 Ωm or conductivity 2.22·10 7 S/m—are comparable to the best results for commercial inks, and five times better than achieved in research on modification of commercial ink in which sintering was conducted in comparable temperatures (2.3·10 −7 Ωm) 26 . A higher value of conductivity was achieved in research where authors used an alternative approach of reactive silver ink solution instead of nanoparticle-based (4.6·10 −7 S/m) 27 and lower value of resistivity in research where the authors add carbon nanotubes to commercial ink and sinter them at temperature 350 °C (2.8·10 −8 Ωm) 4 .…”

“…Oakley 24 was 1.2·10 7 S/m, and M.Morales—Rodrigues 25 achieve even 2.38·10 7 S/m. Several pieces of research modify commercial inks to improve their conductivity, and while solvent addition didn't lower the resistivity 26 of ink sintered at low temperature (140–160 °C), SWCNT addition to ink sintered at temperature 350 °C lower the resistivity of the commercial ink 27 , achieving 2.8·10 −8 Ωm. A novel alternative approach of reactive silver ink solution instead of nanoparticle-based results in even higher conductivity 4 4.6·10 −7 S/m.…”

Electroplating of Aerosol Jet‐Printed Silver Inks

“…Numerous techniques have been investigated to improve the conductivity of printed conductive contacts on nonideal temperature-sensitive substrates including the use of reactive inks, photonic sintering, and electroplating. Currently, reactive inks yield the lowest resistivity, [26] but can suffer from high DOI: 10.1002/adem.202100362 Aerosol jet printing of silver inks is a promising approach for 3D printing of electronics, particularly for obtaining very complex circuits with high-resolution conductive pads and traces. Common silver inks are however not competitive with traditional bulk metal conductors, requiring sintering at high temperatures as well as having significant porosity that can result in early failure.…”