Sometimes, innovation can be born out of coincidence. When MIT researchers were 3D printing magnetic coils out of polymer filament doped with copper nanoparticles, they noticed an unexpected quality in the material: it had a high resistance to electrical currents, and its levels would return to their original states when the flow of electrical current stopped. Why is this important? This is the quality that allows engineers to make transistors that can operate as swtiches. With this discovery, the MIT researchers had a new goal: to create the first fully 3D-printed, semiconductor-free, solid-state logic gates, and the first fully 3D-printed resettable fuses. The team succeeded, and this July, they published a paper on their devices.
Logic gates are devices that perform logical operations based on one or more binary inputs and produce one binary output—essentially, performing computation. Typically, they require semiconductors (often silicon or other materials), which have adaptable electrical properties. Silicon, for example, can have conductive and insulating regions depending on how its modified, making it optimal for producing transistors. Keeping in mind that transistors are the foundation of modern electronics, it’s notable that semiconductor devices are not widely available. They require specialized manufacturing facilities, and during the COVID-19 pandemic, the lack of semiconductor production facilities was one of the causes of the electronics shortage.
The 3D printed device and visualizations of its thermal conductivity (Photo credits: MIT)
So, the potential to create logic gates without the need for semiconductors opens the possibility for electronics to be created on a local level. The idea is still far from being a reality, but MIT researchers took a critical step towards that goal by 3D printing switches for logic gates. The production process used less energy and produced less waste than producing semiconductors, in part because the switches were printed using standard 3D printing hardware and inexpensive, biodegradable copper-doped polymer.
The MIT researchers experimented with using different 3D printing filaments, including polymers doped with carbon, carbon nanotubes, and graphene, but none could function as a resettable fuse. According to MIT’s article covering the subject, “[The researchers] hypothesize that the copper particles in the material spread out when it is heated by the electric current, which causes a spike in resistance that comes back down when the material cools and the copper particles move closer together. They also think the polymer base of the material changes from crystalline to amorphous when heated, then returns to crystalline when cooled down — a phenomenon known as the polymeric positive temperature coefficient.”
Luis Fernando Velásquez-García, a principal research scientist in MIT’s Microsystems Technology Laboratories (MTL) and senior author of a paper describing the devices, says that they still need to do more research to discover why the copper-doped polymer reacts the way it does. The device didn’t perform as well as silicon-based transistors, but it could be used for simple control functions like turning a motor on and off. Even after 4,000 rounds of testing the switch, the transistor didn’t show signs of deterioration.
Will There Be 3D Printed Electronics in the Future?
“This technology has real legs,” Velásquez-García said. “While we cannot compete with silicon as a semiconductor, our idea is not to necessarily replace what is existing but to push 3D printing technology into uncharted territory. In a nutshell, this is really about democratizing technology. This could allow anyone to create smart hardware far from traditional manufacturing centers.”
In their paper, published in the Virtual and Physical Prototyping journal, the researchers claimed that “the customizability and accessibility intrinsic to material extrusion additive manufacturing make this technology promisingly disruptive.” Their study concluded, “This work serves as a steppingstone for the semiconductor-free democratization of electronic device fabrication and is of immediate relevance for the manufacture of custom, intelligent devices far from traditional manufacturing centers.”
MIT reported that going forward, the researchers want to use this technology to print fully functional electronics. Right now, they’re aiming to create a magnetic motor with only extrusion 3D printing. Additionally, they also want to finetune the process so they could build more complex circuits and see how far they can push the performance of these devices. For more details on the study, read MIT’s article here.
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