3D printing may be used to custom manufacture electronics.

A group of researchers from the Naval Research Laboratory in Washington, DC, has demonstrated that combining two technologies—one to create a thin film and the second to “cut” designs out of the film—could be a powerful tool to create custom electronic components.

Fig. 1 - A scanning electron microscope image shows a pyramid structure made of silver paste. The pyramid, which was created by multiple laser pulses, shows how a 3D structure can be built up.
“I think of additive manufacturing as the democratization of manufacturing,” said Eric Breckenfeld, a National Research Council Fellow at the Naval Research Laboratory. He says that the lower equipment costs associated with additive manufacturing means that the technology can be a great fit for rapid prototyping and be used by small labs and start-up companies with limited funds.

One additive manufacturing technique that’s gaining traction is called Laser Induced Forward Transfer (LIFT). In LIFT, a laser beam passes over a thin film of ink or paste. The ink absorbs the laser energy, which vaporizes a thin layer of solvent. The vaporized solvent gas rapidly expands, and the ink or paste is ejected from the film at very high speeds. One advantage of LIFT is that it can transfer high viscosity inks and pastes.

“LIFT can transfer pastes that are almost solid, like the consistency of toothpaste,” Breckenfeld explains. “An ink jet printer couldn’t handle toothpaste.”

How It Works

LIFT was first developed in the 1980s as a way to eject molten droplets from thin copper films. Naval Research Lab scientists later developed the technique to print fluids and nano-powder suspensions. The team is now turning to new materials, most recently to inks containing the transition-metal oxide vanadium dioxide (VO2). Vanadium dioxide undergoes a sharp semiconductor-to-metal phase transition near room temperature, which makes it an attractive material for a wide range of applications, including chemical sensors, ultra-fast electrical and optical switches, and coatings that change color with temperature.

To turn vanadium dioxide into a thin film compatible with LIFT, the team of researchers turned to another newly developed technology, called polymer assisted deposition (PAD). PAD works by dissolving metal salts in a solution containing polymers. The metal ions bind to the polymer, forming a stable structure. The solution is then placed on a spinning disk that spreads it into a thin film, which is later cured in an oven to decompose the polymer.

Previously, there was not much overlap between groups studying the two technologies, Breckenfeld said. He and his colleagues explored a variety of solvents and heating steps to optimize the growth of vanadium dioxide films on glass and crystalline substrates. They then experimented using LIFT to print patterns with the PAD solutions. (See Figure 1)

“The transfer step proved to be the most challenging,” Breckenfeld explained. In order for LIFT to work, the thin film materials must absorb the wavelength of light of the LIFT laser. The researchers had to modify the vanadium dioxide PAD solutions to catch the energy of the laser light.

So far, the team has successfully printed simple patterns. Breckenfeld said the results show that LIFT and PAD technologies combined could directly print a wide range of commercially attractive electronic materials. The researchers plan to extend their own experiments to new materials soon.

The team’s findings, “Laser Induced Forward Transfer of High-Viscosity, Polymer-Based VO2 Inks,” were presented at the AVS 62nd International Symposium and Exhibition, held in October. AVS is an interdisciplinary, professional society that supports networking among academic, industrial, government, and consulting professionals.

For more information, visit www.avs.org .