Energetic electronics — components that may control electrical signals — often contain semiconductor devices that receive, store, and process information. These components, which have to be made in a clean room, require advanced fabrication technology that shouldn’t be widely available outside just a few specialized manufacturing centers.
In the course of the Covid-19 pandemic, the dearth of widespread semiconductor fabrication facilities was one reason for a worldwide electronics shortage, which drove up costs for consumers and had implications in every part from economic growth to national defense. The flexibility to 3D print a whole, energetic electronic device without the necessity for semiconductors could bring electronics fabrication to businesses, labs, and houses across the globe.
While this concept continues to be far off, MIT researchers have taken a crucial step in that direction by demonstrating fully 3D-printed resettable fuses, that are key components of energetic electronics that typically require semiconductors.
The researchers’ semiconductor-free devices, which they produced using standard 3D printing hardware and an affordable, biodegradable material, can perform the identical switching functions because the semiconductor-based transistors used for processing operations in energetic electronics.
Although still removed from achieving the performance of semiconductor transistors, the 3D-printed devices might be used for basic control operations like regulating the speed of an electrical motor.
“This technology has real legs. While we cannot compete with silicon as a semiconductor, our idea shouldn’t be to necessarily replace what’s existing, but to push 3D printing technology into uncharted territory. In a nutshell, this is admittedly about democratizing technology. This might allow anyone to create smart hardware removed from traditional manufacturing centers,” says Luis Fernando Velásquez-GarcÃa, a principal research scientist in MIT’s Microsystems Technology Laboratories (MTL) and senior writer of a paper describing the devices, which appears in Virtual and Physical Prototyping.
He’s joined on the paper by lead writer Jorge Cañada, an electrical engineering and computer science graduate student.
An unexpected project
Semiconductors, including silicon, are materials with electrical properties that could be tailored by adding certain impurities. A silicon device can have conductive and insulating regions, depending on the way it is engineered. These properties make silicon ideal for producing transistors, that are a basic constructing block of recent electronics.
Nonetheless, the researchers didn’t got down to 3D-print semiconductor-free devices that might behave like silicon-based transistors.
This project grew out of one other during which they were fabricating magnetic coils using extrusion printing, a process where the printer melts filament and squirts material through a nozzle, fabricating an object layer-by-layer.
They saw an interesting phenomenon in the fabric they were using, a polymer filament doped with copper nanoparticles.
In the event that they passed a considerable amount of electric current into the fabric, it might exhibit an enormous spike in resistance but would return to its original level shortly after the present flow stopped.
This property enables engineers to make transistors that may operate as switches, something that is often only related to silicon and other semiconductors. Transistors, which turn on and off to process binary data, are used to form logic gates which perform computation.
“We saw that this was something that might help take 3D printing hardware to the following level. It offers a transparent approach to provide some extent of ‘smart’ to an electronic device,” Velásquez-GarcÃa says.
The researchers tried to copy the identical phenomenon with other 3D printing filaments, testing polymers doped with carbon, carbon nanotubes, and graphene. Ultimately, they may not find one other printable material that might function as a resettable fuse.
They hypothesize that the copper particles in the fabric unfolded when it’s heated by the electrical current, which causes a spike in resistance that comes back down when the fabric cools and the copper particles move closer together. In addition they think the polymer base of the fabric changes from crystalline to amorphous when heated, then returns to crystalline when cooled down — a phenomenon generally known as the polymeric positive temperature coefficient.
“For now, that’s our greatest explanation, but that shouldn’t be the complete answer because that does not explain why it only happened in this mix of materials. We’d like to do more research, but there isn’t any doubt that this phenomenon is real,” he says.
3D-printing energetic electronics
The team leveraged the phenomenon to print switches in a single step that might be used to form semiconductor-free logic gates.
The devices are made out of thin, 3D-printed traces of the copper-doped polymer. They contain intersecting conductive regions that enable the researchers to manage the resistance by controlling the voltage fed into the switch.
While the devices didn’t perform in addition to silicon-based transistors, they might be used for less complicated control and processing functions, akin to turning a motor on and off. Their experiments showed that, even after 4,000 cycles of switching, the devices showed no signs of degradation.
But there are limits to how small the researchers could make the switches, based on the physics of extrusion printing and the properties of the fabric. They may print devices that were just a few hundred microns, but transistors in state-of-the-art electronics are only few nanometers in diameter.
“The truth is that there are lots of engineering situations that do not require the perfect chips. At the tip of the day, all you care about is whether or not your device can do the duty. This technology is capable of satisfy a constraint like that,” he says.
Nonetheless, unlike semiconductor fabrication, their technique uses a biodegradable material and the method uses less energy and produces less waste. The polymer filament may be doped with other materials, like magnetic microparticles that might enable additional functionalities.
In the long run, the researchers need to use this technology to print fully functional electronics. They’re striving to fabricate a working magnetic motor using only extrusion 3D printing. In addition they need to finetune the method in order that they could construct more complex circuits
This work is funded, partly, by Empiriko Corporation.
