3D-printed electronics

Advances in software, materials and equipment have made it possible to cheaply ‘print’ custom designs, including diverse products such as airplane engines and action figures.

Researchers from the Naval Research Laboratory in Washington DC have demonstrated that a combination of two technologies — one to create a thin film and the second to ‘cut’ designs out of the film — could be a potentially powerful tool to create custom electronic components.

Eric Breckenfeld, a National Research Council Fellow at the Naval Research Laboratory, said the lower equipment costs associated with additive manufacturing mean the technology is a great fit for rapid prototyping and can be used by small labs and start-up companies with limited funds.

One additive manufacturing technique that is gaining traction is called laser-induced forward transfer, or LIFT. In LIFT, a laser beam passes over a thin film of ink or paste. The ink absorbs the laser energy, which vaporises a thin layer of solvent. The vaporised 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 said. “An ink jet printer couldn’t handle toothpaste.”

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 continues to push the technique to new materials, turning most recently to inks containing the transition-metal oxide vanadium dioxide.

Vanadium dioxide undergoes a sharp semiconductor-to-metal phase transition near room temperature, making it an attractive material for a wide range of applications, including chemical sensors, ultrafast electrical and optical switches, and coatings that change colour with temperature.

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

Breckenfeld and his colleagues explored a variety of solvents and heating steps to optimise the growth of vanadium dioxide films on glass and crystalline substrates. They then experimented using LIFT to print patterns with the PAD solutions. 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.