Reviewed by Lexie CornerNov 11 2024
Researchers at Yokohama National University have created a promising bubble printing technique that enables the precise patterning of liquid metal wiring for flexible electronics. This method opens up new possibilities for making highly conductive, stretchable, and bending circuits, which are perfect for wearable sensors and medical implants. Their findings were published in the journal Nanomaterials.
Through laser-induced microbubbles, EGaIn colloidal particles are precisely arranged on a glass surface, creating ultrathin, conductive, and flexible wiring. Image Credit: Yokohama National University
Wiring technologies are essential in our daily lives, establishing connections between electronic components to distribute power and signals throughout devices. Most electronics, such as computers and phones, rely on traditional wiring made of physical wires and circuit boards. However, as the demand for wearable electronics increases, conventional wiring is beginning to face limitations.
Conventional wiring technologies rely on rigid conductive materials, which are unsuitable for flexible electronics that need to bend and stretch.
Shoji Maruo, Professor and Study Corresponding Author, Faculty of Engineering, Yokohama National University
Although liquid metals and other alternatives to rigid materials show promise, their use presents several difficulties.
Liquid metals provide both flexibility and high conductivity, yet they present issues in wiring size, patterning freedom, and electrical resistance of its oxide layer.
Masaru Mukai, Assistant Professor and Study First Author, Faculty Of Engineering, Yokohama National University
To overcome these limitations, the research team applied a bubble printing technique, which has traditionally been used with solid particles, to pattern liquid metal colloidal particles of eutectic gallium-indium alloy (EGaIn).
Bubble printing is a cutting-edge method that uses the flow generated by bubbles to move particles. This enables the creation of precise wiring patterns directly onto surfaces, especially on flexible or non-traditional substrates.
The team used a femtosecond laser beam to heat the EGaIn particles, generating microbubbles that directed the particles into exact lines on a flexible glass surface.
“The key is to improve conductivity by replacing the resistive gallium oxide layer with conductive silver via galvanic replacement,” Maruo said.
The resultant wiring lines were extremely flexible, thin, and conductive.
Our liquid metal wiring, with a minimum line width of 3.4 μm, demonstrated a high conductivity of 1.5 × 105 S/m and maintained stable conductivity even when bent, highlighting its potential for flexible electronic applications.
Masaru Mukai, Assistant Professor and Study First Author, Faculty Of Engineering, Yokohama National University
This technique enables the creation of soft electronics for wearable technology and healthcare applications, where both accuracy and flexibility are essential, by producing reliable, ultra-thin liquid metal wiring.
The team plans to further enhance the elasticity and flexibility of their liquid metal wire by incorporating even more versatile substrates.
Our ultimate goal is to integrate this method with electronic components, such as organic devices, enabling practical, flexible devices for everyday use. We see potential applications in areas like wearable sensors, medical devices, and other technologies that require flexible, durable wiring.
Shoji Maruo, Professor and Study Corresponding Author, Faculty of Engineering, Yokohama National University
The study was funded by Tatsuya Kobayashi, Mitsuki Sato, Juri Asada, Kazuhide Ueno, and Taichi Furukawa at Yokohama National University. JST CREST JPMJCR1905 helped support the study.
Journal Reference:
Mukai, M., et al. (2024) Bubble Printing of Liquid Metal Colloidal Particles for Conductive Patterns. Nanomaterials. doi.org/10.3390/nano14201665.