Printed electronic circuits are integral parts of low-cost sensors and other devices, but they’ve been limited to the 2-D domain. Researchers have now pulled printed circuits into the third dimension by developing a simple method to deposit multiple electronic materials on complex 3-D structures (Nat. Electron. 2020, DOI: 10.1038/s41928-020-0391-2).
3-D printing has become a common commercial tool to make aircraft parts, toys, and even face shields and medical device parts for emergency responders and hospitals treating people who have COVID-19. Creating complex, custom-designed structures is the method’s forte.
But 3-D printing electronic devices is still a challenge, in large part because they tend to require integrating different kinds of materials. Making devices with multiple materials typically takes hours if not weeks of printing in several stages, with breaks to embed wires or spray inks on the printed surfaces, says Xiaoyu Zheng, a mechanical engineer at the University of California, Los Angeles. He and his team wanted to speed the process up.
Zheng and his colleagues developed a process for rapidly making functional electronic devices on complex 3-D printed architectures. The key is the use of patterned electrical charges to program the coating of electronic materials using patterned charges.
The method is based on a 3-D printing technique called stereolithography, which shines ultraviolet light in pre-programmed patterns on a liquid resin in a vat to polymerize it and create a solid object. Zheng’s group made three different stereolithography resins, carrying either a positive, negative, or neutral charge, and used them to make complex structures with distinctly charged parts.
Next, they dipped the resulting structures into a solution containing a palladium catalyst that’s either positively or negatively charged. The catalyst coats parts of the structure with the opposite charge. The researchers immersed the object into a chemical plating solution containing a functional electronic material. The catalyst triggered the material to coat specific areas based on their intrinsic charge.
By repeating this step with the catalyst of the opposite charge, the team could deposit a combination of any two materials on the 3-D objects, including metals such as copper and nickel, magnetic iron oxide, semiconducting zinc oxide, and even carbon nanotubes. But Zheng says “you can use any functional material that you can physically or chemically attach.” The neutral, uncoated 3-D printed polymer structures can serve as an insulating material or dielectric in electronic devices.
To demonstrate the technique’s practicality, the researchers made a flexible touch sensor. They printed a porous 3-D mesh with a resin containing piezoelectric lead-zirconate-titanate nanoparticles that convert pressure into electricity, then patterned copper electrodes on top. They also created a 3-D antenna array using a combination of polymer dielectric and copper. Zheng says they are now exploring applications such as antenna arrays for 5G communications, and 3-D sensor arrays for soft robots and wearables.
Zhigang Wu, a mechanical engineer at Huazhong University of Science and Technology calls this method a breakthrough, praising its versatility in using a single process to print all essential materials for electronics. The process needs further work to scale up for mass production, but it could be important for circuit design and prototyping.