If a phone or other electronic device were made from soft materials, how would that change its use? Would it be more durable? If hospital medical monitoring equipment were made from less rigid components, would it be easier for patients to wear?
Although this type of electronics is still far in the future, researchers from Virginia Tech have developed an innovative method for constructing the flexible electronic components that constitute them. A project by the team of Michael Bartlett, principal investigator and associate professor in the department of mechanical engineering, focuses on the circuits that manage all the electronic connections inside.
Published in Nature Electronics, this new technique uses liquid metal microdroplets to create a staircase-like structure that forms small conductive passages called “vias”. These vias create electrical connections across and between layers of the circuit without the need to drill holes in the hardware, as was the case with previous techniques.
« This brings us closer to exciting possibilities such as advanced soft robotics, wearable devices and electronics that can stretch, bend and twist while maintaining high functionality “, said Mr. Bartlett.
The publication’s first author is Dong Hae Ho, a postdoctoral researcher working with Bartlett. The Virginia Tech team was joined in this study by their colleagues Ling Liassociate professor at theuniversity of pennsylvaniaand Chenhao Hu, a doctoral student in Li’s team.
The work was funded by the Office of Naval Research Young Investigator Program grant and the National Science Foundation Early Faculty Career Development (CAREER) grant, as well as support from Virginia Tech.
This flexible circuit has two different layers, a top layer with nine LEDs and a bottom layer with nine sensors linked together by 21 liquid metal connections across the layers. The total thickness is similar to that of a few sheets of paper. Courtesy of Michael Bartlett.
Soft electronics, vias and interconnections
THE previous research on flexible circuits carried out by Bartlett’s team replace rigid materials with soft electronic composites and tiny electrically conductive liquid metal droplets. These flexible electronic circuits are part of a growing field of technology that gives gadgets a new level of durability.
In this project, researchers tackled the problem of flexible printed circuits, in particular the passage of electrical currents between layers that stack on top of each other. This is important for making good use of electrical current in the limited space occupied by printed circuit boards.
While conventional rigid electronics use well-established techniques to create vias, which are essential for making the multilayer electronics common today, they often require drilling holes through a circuit board, which works when materials Rigid layers are used to connect these layers. In soft material, where a drilled hole can stretch, current control requires a different approach.
The team’s new technique does not make holes and uses microdroplets of liquid metal to form flexible vias and planar interconnects, creating electrical connections across and between circuit layers, thereby overcoming these difficulties. The process involves the directed layering of liquid metal droplets inside a photoresist. By exploiting the irregularities that appear during ultraviolet exposure, the researchers create a staircase-like structure that allows droplets to assemble in a controlled manner in 3D.
This approach is very versatile, and these liquid metal vias and interconnects can be implemented in several material types. Researchers can go further and perform the manufacturing approach multiple times and create more and more layers.
Using a bug as a feature
In known methods of creating electronic components and other micro- and nanotechnologies, ultraviolet exposure causes imperfections known as mask edge anomalies or undercuts, which typically cause problems in standard manufacturing. However, the researchers turned this problem into a feature: The edges of the ultraviolet-exposed areas cause the liquid metal droplets to settle and stratify in a vertical, step-like pattern. This directed assembly allows the droplets to form a continuous path through the photoresist, connecting the top and bottom layers, which is then fully cured to lock the configuration in place. This process occurs simultaneously and droplet settling is rapid, so the process of creating multiple holes takes less than a minute.
« By taking advantage of these otherwise undesirable edge effects, we can create flexible conductive holes that connect different circuit layers in a fast, parallel manner. », explains M. Ho. « We can do this while maintaining the flexibility and mechanical integrity of the soft device. »
« By integrating in-plane and across-plane circuit layers, it is possible to create soft, flexible circuits with complex multi-layer architectures ” Bartlett said. “ This enables new forms of flexible electronics, where multiple vias and flexible interconnections are created in a parallel and spatially controlled manner. This is essential to moving the field forward. »
In summary
This advance in the field of flexible electronics represents a disruptive innovation with considerable implications. The technique developed by the Virginia Tech team, using microdroplets of liquid metal, offers an elegant solution to the challenges of flexible electronics. While this technology has undeniable advantages in terms of flexibility and adaptability, it should nevertheless be noted that we are still in the early stages of its development. The potential applications, particularly in the medical field and flexible robotics, are promising, but will still require testing and optimization phases before large-scale commercialization.
For a better understanding
What makes this innovation different from traditional electronic circuits?
Unlike traditional circuits that require drilling holes, this new technique uses microdroplets of liquid metal forming a staircase structure, allowing flexibility while maintaining electrical conductivity.
How did researchers turn a flaw into an advantage?
Mask edge anomalies, traditionally considered defects in standard manufacturing, have been exploited to create a system for controlled deposition of liquid metal droplets, thereby forming efficient electrical connections.
What are the potential areas of application for this technology?
This innovation could revolutionize soft robotics, wearable medical devices, and consumer electronics with devices capable of bending, stretching, and twisting while maintaining functionality.
What are the main advantages of this new approach?
The technique enables rapid, parallel and controlled manufacturing of electrical connections, while maintaining the flexibility and mechanical integrity of the devices. It is also adaptable to different types of materials.
What are the remaining challenges before a commercial application?
Although promising, the technology still requires development to ensure its long-term sustainability, large-scale production and integration into existing industrial manufacturing processes.
Source : Virginia TECH – Traduction Enerzine.com
Illustration caption: (Left to right) Postdoctoral researcher Dong Hae Ho and Associate Professor Michael Bartlett examine a flexible electronic circuit made using their flexible circuit production method. Credit: Alex Parrish / Virginia Tech.
