Inkjet Printing of Particle-Free Platinum Inks

  • Timothy David Grant

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

This thesis investigates the inkjet printing of a high-concentration (20wt%) particle-free platinum (Pt) ink. Inkjet printing is an evolving method of manufacturing electronics by additive manufacturing, which has advantages over traditional processes due to the minimal waste generated and the adaptability of the process to multiple applications.

Manufacturing electronics by inkjet printing is covered in existing literature primarily relating to the deposition of silver (Ag) and gold (Au) inks in nanoparticle form. These nanoparticles are typically suspended within a solvent and are prone to agglomerating leading to the blocking of the printer nozzles. Particle-free conductive inks typically compromise conductive metal particles dissolved in a carrier solution that theoretically form more uniform conductive films with a reduced risk of the printer nozzles blocking. The inkjet printing of Pt films is much less common in existing literature yet being a rare earth metal, Pt is well suited for inkjet printing as this additive manufacturing method theoretically minimises material wastage and forms higher resolution printed features (up to 40μm) versus more traditional approaches such as screen printing and spin coating.

Before jetting with the Pt ink, a blank ink formulated with the same solvents as the Pt ink but without the Pt content was evaluated to determine the necessity and volume of viscosity modifier required for reliable jetting of single droplets within a Dimatix inkjet printer. Using a blank ink with 80% viscosity modifier by volume, an inverse Ohnesorge (Z) number of 2.46 was obtained, within the identified printable region of 1 < Z < 14.

This ratio was used to inform the quantity of viscosity modifier added to the Pt-containing ink, where Z was measured as 1.83, within the printable region. Droplets of ink were ejected from the printer simultaneously from up to four nozzles at 7m/s - 9m/s. Pt films up to 33nm thick were formed with a conductivity of 1.7MS/m, greater than a 100% increase over films printed identically with a lower concentration 10wt% Pt ink.

Conductive films were also evaluated in terms of feature definition (109%), substrate adhesion (stable for multi-layer films), minimum resolution (43.2μm), surface quality (39% maximum porosity and 0.023μm² maximum void size) and elemental composition (62.02wt% Pt in printed films). Applications of printed Pt films were then investigated including temperature sensors, Schottky diode electrodes and retroreflectors. The latter involved an in-depth study of manufacturing low-cost reflective surfaces for use in surveying equipment, the printed Pt reflective panels were 58% reflective at 795nm.

In summary, this thesis illustrates that conductive Pt films may be formed with a high-concentration particle-free Pt ink. The features of the films are evaluated and applications demonstrated, providing a reference for future development with this ink.
Date of Award2023
Original languageEnglish
SupervisorAmin Abdolvand (Supervisor) & Thomas Jones (Supervisor)

Keywords

  • Inkjet
  • Platinum
  • Particle-free
  • Conductive
  • Reflective

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