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3D printing is revolutionizing the fields of prototyping and manufacturing, scaling from hyper-local customized one-off creations to mass-produced buildings and more. The next logical step: To be able to print active electronics, creating complex devices in a single stage — something engineers from the University of Minnesota, some now at the Massachusetts Institute of Technology, the Korea Institute of Industrial Technology, and the Pusan National University, claim to have achieved.

In their paper published in Science Advances, the team has showcased an approach for manufacturing a functional display based on an 8×8 matrix of organic light-emitting diodes (OLEDs) — without the need to perform any kind of manufacturing beyond two forms of 3D printing, both achievable using a customized table-top 3D printer.

Printed electronics

Printing solid objects and simple mechanical devices is a largely-solved problem, but making a 3D printer spit out functional electronics is considerably more challenging. Many approaches rely on partial 3D printing followed by the integration of electronics made in a more traditional manner, or limit the complexity of the components they can create.

The display printed at the University of Minnesota, by contrast, is a surprisingly complex creation — and one the manufacture of which is typically restricted to clean-room environments and specialized equipment.

“OLED displays are usually produced in big, expensive, ultra-clean fabrication facilities,” Michael McAlpine, professor and senior author of the work, explains. “We wanted to see if we could basically condense all of that down and print an OLED display on our table-top 3D printer, which was custom built and costs about the same as a Tesla Model S.”

While it’s true that a 3D printer as expensive as a Tesla Model S — just shy of $100,000 for the base trim at the time of writing — isn’t something most people will have in their office or garage, it’s considerably cheaper than the manufacturing facilities typically required for an OLED display panel.

The printer, described by the team as a “‘one-pot’ 3D printing platform,” works through the combination of multiple processing approaches: Material extrusion, spraying, and mechanical reconfiguration — and all without ever requiring anything beyond the printer itself, small enough to sit atop a desk, and a day-long treatment in a vacuum desiccator to cure its functional inks.

A successful display

“I thought I would get something, but maybe not a fully working display,” says Ruitao Su, first author of the paper, of the device his team created. “But then it turns out all the pixels were working, and I can display the text I designed. My first reaction was ‘it is real!’ I was not able to sleep, the whole night.”

While the display itself is rudimentary — an 8×8 matrix totaling 64 OLED devices offering a variable brightness across a single color — it’s an important proof-of-concept which brings a surprising advantage to the table: It’s flexible, bending and springing back into shape in a way which would make it well-suited to use in wearables and other devices with non-planar geometries.

“The device exhibited a relatively stable emission over the 2,000 bending cycles,” Su explains, “suggesting that fully 3D printed OLEDs can potentially be used for important applications in soft electronics and wearable devices.”

The six-layer display is entirely 3D-printed using a single customized desktop printer.

The display is built up of six layers 3D-printed on polyethylene tetraphthalate (PET) film: An interconnect layer printed with conductive inks containing silver nanoparticles; a thin-film array of a conductive polymer as the anode structure; a thin-film array of an electroluminescent polymer which gives the display its glow; a silicone-based insulation layer; a droplet layer which is reconfigured by the printer to form the cathode structure; and a top interconnect layer. Finally, the whole device is encapsulated using an extrusion-printed silicone mold.

The reconfiguration step is of particular interest. Described by the team as “analogous to conventional metal forging,” the droplets are compressed using a polypropylene nozzle mounted to the 3D printer. After tuning the compression rate, dwell time, and depth, the team found a way to reconfigure the droplets such that they had a similar height but exhibited an increased contact area with the layer below — solving one of the key difficulties which had previously plagued 3D-printed electronics.

Real-world potential

The approach taken by the team shows considerable promise, in particular because even expensive 3D printers are cheaper than traditional factories. “Our printing methodology for both thin-film and metallization layers circumvented the need for photomask sets, cleanrooms, or complicated circuit layouts involved in conventional microelectronics fabrication,” the researchers note.

Performance of the resulting display — for all its low resolution — proves the concept still further: In testing, the 3D-printed display offered a response time of 0.2ms — “on the same order of magnitude,” its creators write, “as inorganic aluminum gallium indium phosphide (AlGaInP) LEDs and one order of magnitude faster than typical LCDs.”

The device’s robustness, too, impresses, offering “relatively stable [light] emission over 2,000 bending cycles,” and successfully displaying text and images even when bent nearly completely in half.

Printed onto a flexible substrate, the display is capable of operating while bent nearly double.

It’s the manufacturing process that is the highlight of the work, though. “The ability to fabricate OLED displays entirely on 3D printing platforms represents a paradigm shift for the printing of optoelectronics,” the paper’s authors claim, “which will affect other types of active devices, such as image sensors, photovoltaics, and computation.”

The team’s next step: Creating displays with improved resolution, improving the inks in use, and finding a way to integrated controlling circuits — including transistors and capacitors — to create a fully 3D-printed active-matrix display.

The paper detailing the work is available under open-access terms in the journal Science Advances.

Reference

Ruitao Su, Sung Hyun Park, Xia Ouyang, Song Ih Ahn, Michael C. McAlpine: 3D-printed flexible organic light-emitting diode displays, Science Advances Vol 8, Issue 1. DOI 10.1126/sciadv.abl8798.