Beyond wires: Bubble printing technology powers next-generation electronics

Researchers at Yokohama National University have developed a promising bubble printing method that enables high-precision patterning of liquid metal interconnects for flexible electronics. This technology provides new options for creating bendable, stretchable, and highly conductive circuits that are ideal for devices such as wearable sensors and medical implants. Their study was published in the journal Nanomaterials on October 17th.

Wiring technology is a part of our daily life. This technology creates pathways to connect electronic components and transmit signals and power throughout the device. Traditional wiring, consisting of physical wires and circuit boards, provides power to most electronic devices, from phones to computers. However, as the demand for wearable electronic devices increases, it has become clear that traditional wiring is insufficient.

“Traditional interconnect technologies rely on rigid conductive materials, making them unsuitable for flexible electronics that need to be bent and stretched,” said Shoji Maruo, a professor at Yokohama National University’s School of Engineering and corresponding author of the study. Ta.

Alternatives to such hard materials, such as liquid metals, are promising, but their use poses certain challenges.

“Liquid metals offer both flexibility and high conductivity, but they have issues with interconnect size, patterning freedom, and electrical resistance of the oxide layer,” said Masaru Mukai, assistant professor in the School of Engineering and lead author of the study. said.

The research team addressed these limitations by employing a bubble printing method traditionally used for solid particles to pattern liquid metal colloidal particles of eutectic gallium indium alloy (EGaIn). Bubble printing is an advanced technique for creating precise wiring patterns directly on surfaces, especially non-conventional or flexible substrates, using particles moved by a flow generated by bubbles.

The researchers used a femtosecond laser beam to heat the EGaIn particles, creating microbubbles that guided the particles into precise lines on a flexible glass surface.

“The key is to improve conductivity by replacing the resistive gallium oxide layer with conductive silver through electrical displacement,” Maruo said.

The resulting wiring lines were not only incredibly thin and conductive, but also extremely flexible.

“Liquid metal interconnects with a minimum line width of 3.4 μm exhibited high conductivity of 1.5 × 105 S/m and remained stable conductivity even when bent. This highlights its potential for flexible electronic applications. “We are doing so,” Mukai said.

By achieving reliable ultrathin liquid metal interconnects, this method opens up the possibility of creating soft electronics in wearable technology and healthcare applications where both flexibility and precise functionality are essential.

The research team aims to further enhance the flexibility and elasticity of liquid metal interconnects by incorporating more flexible substrates.

“Our ultimate goal is to integrate this method with electronic components, such as organic devices, to enable practical and flexible devices for everyday use,” Maruo said. “We think it has potential applications in areas such as wearable sensors, medical devices, and other technologies that require flexible and durable wiring.”