CHARM3D process fabricates free-standing, self-healing, three-dimensional electronic circuits.
A team of researchers from the National University of Singapore (NUS) has developed a new technique – known as tension-driven CHARM3D – to fabricate three-dimensional, self-healing electronic circuits. In contrast to previous approaches, this new technique enables the 3D printing of free-standing metallic structures without requiring support materials and external pressure.
Led by associate professor Benjamin Tee from the Department of Materials Science and Engineering, the researchers used Field’s metal to demonstrate how CHARM3D can fabricate a wide range of electronics, allowing for more compact designs in devices such as wearable sensors, wireless communication systems and electromagnetic metamaterials.
In healthcare, for instance, CHARM3D could facilitate the development of contactless vital sign monitoring devices. In signal sensing, it could optimise the performance of 3D antennas, leading to improved communication systems, more accurate medical imaging and robust security applications.
Streamlining 3D circuit manufacturing
According to the research team, direct ink writing (DIW), another 3D printing technique that’s currently used to fabricate 3D circuits, has some significant drawbacks. The crux lies in its use of composite inks, which have low electrical conductivity and require support materials to aid in solidification after printing. The inks are also too viscous, limiting printing speed.
Enter Field’s metal, a eutectic alloy of indium, bismuth and tin. Eutectic alloys melt and freeze at a single temperature lower than the melting points of their constituent metals — offering an attractive alternative material for 3D printing. With a low melting point of 62 degrees Celsius, a high electrical conductivity and low toxicity, Field’s metal, unlike composite inks, solidifies rapidly. This crucial characteristic enables the printing process to eschew support materials and external pressure.
Leveraging the low melting point of Field’s metal, the CHARM3D technique exploits the tension between molten metal in a nozzle and the leading edge of the printed part, culminating in uniform, smooth microwire structures with adjustable widths of 100 to 300 microns. Critically, phenomena such as beading and uneven surfaces — characteristic of pressure-driven DIW — are also absent in CHARM3D.
The researchers claim that, compared to conventional DIW, CHARM3D offers faster printing speeds of up to 100 millimetres per second and higher resolutions. CHARM3D also forgoes post-treatment steps and enables the fabrication of complex free-standing 3D structures, such as vertical letters, cubic frameworks and scalable helixes. Moreover, the researchers found that these 3D architectures exhibit excellent structural retention with self-healing capabilities, and they’re recyclable to boot.
“By offering a faster and simpler approach to 3D metal printing as a solution for advanced electronic circuit manufacturing, CHARM3D holds immense promise for the industrial-scale production and widespread adoption of intricate 3D electronic circuits,” said Tee.
3D printed circuit applications
The researchers successfully printed a 3D circuit for wearable battery-free temperature sensors, antennas for wireless vital sign monitoring and metamaterials for electromagnetic wave manipulation — showcasing the diversity in applications enabled by CHARM3D.
Traditional hospital equipment such as electrocardiograms and pulse oximeters require skin contact, which can cause discomfort and risk infections. Through CHARM3D, contact-free sensors can be integrated into smart clothing and antennas, providing continuous, accurate health monitoring in hospitals, assisted-living facilities or home settings.
In addition, arrays of 3D antennas or electromagnetic metamaterial sensors could optimise signal sensing and processing applications. This leads to improved signal-to-noise ratios and higher bandwidths. The technique opens up the possibility of creating specialised antennas for targeted communication, enabling more accurate medical imaging, such as microwave breast imaging for early tumour detection, and advanced security applications, such as detecting hidden devices or contraband emitting specific electromagnetic signatures.
The team’s findings were published in the journal Nature Electronics.
