By Ravi Tutika, Post-Doctoral Research Associate at Virginia Tech College of Engineering
Soft and flexible electronics have garnered great attention over the past decade and are rapidly emerging as a novel class of electronic devices of the future. Epidermal health monitoring devices for the health care industry is one such example, while soft robotics and wearable electronics are devices that are highly sought after for human-machine interfacing. Broadly speaking, such devices consist of a combination of soft and stretchable substrates with electronic materials and components integrated in different combinations. The advantage over the traditional rigid PCBs and devices is their conformal nature through which they can be readily deployed over a wide range of complex surfaces. Soft electronics have the mechanical freedom to stretch, twist, bend and be compressed. While the current soft device technology is at the developmental stage, a lot has to be done in order to bring them head-to-head with the rigid PCBs in terms of component density, robustness, and fast paced industrial fabrication for their mass adoption.
One of the major challenges to these devices is damage in unforgiving environments or repeated use in everyday environments. In contrast to traditional electronics that are protected with rigid enclosures, soft electronics need to maintain extreme compliance. General wear and tear can lead to gradual failure or in the event of an unexpected damage, result in failure of either mechanical or functional integrity. To counter these drawbacks, there is a need to design the soft device and materials for electronics with their complete life cycle in mind – fabrication, utility, damage response, and ultimate recyclability. With the increasing emphasis on a greener planet, it is essential to reduce the e-waste generated by ubiquitous electronic devices in our day-to-day life. So, to solve these current challenges and realize the next generation of soft devices, the soft electronics research community have been exploring the use of novel materials and methods in electronics manufacturing.
In the Soft Materials and Structures Lab at Virginia Tech, our design approach is to create regenerative electronic materials by programming in bio-inspired and autonomous functions to protect them from or reverse damage. In our recent paper published in Communications Materials, we employed a room temperature liquid metal (gallium – indium alloy) as dispersed droplets in a highly stretchable elastomer. While being complaint and stretchable, this class of composite materials can enable electrically conductive pathways by an embossing technique leading to a ‘soft PCB’. Through this method, the discrete liquid metal droplets inside the elastomers connect to form robust electrical pathways between respective electronic components. Owing to the re-processable nature of the elastomer matrix and the liquid metal, these materials can be reconfigured during operation to erase old traces and create new electrical pathways on or around them. A key aspect of this material system is the self-healing ability of the created electrical connections. The material has the unique ability to maintain electrical connection by forming a continuous network of liquid metal droplets around a damaged region. As highlighted above, the response of a soft electronic material in a damage event is highly critical for their survival and continued use in various environments and scenarios. And ultimately, if a damage is sustained over a longer period and the material fails, the soft device can be completely recycled back into the soft PCB with dispersed and discrete liquid metal droplets over multiple cycles.
We are very excited and optimistic with our design approach and the material’s capabilities to enable soft electronic technology either exclusively or in combination with current microchip technologies. As this is still a new and emerging field, research is being done to increase the efficiency of these devices and manufacturability for industry adaption. This is expected to result in a greater diversity of such material combinations and fabrication approaches for self-healing soft electronic devices. Fundamentally, a better understanding of interfacial mechanics between different components in these devices and a knowledge of the bulk mechanical and electrical properties that can result in the desired device performance will be a great addition to this field. Utilization of the present manufacturing technologies being employed in large scale industry manufacturing can propel the electronics industry’s involvement and adaptation of these materials.
Currently, the majority of research is at laboratory scale at universities or R&D at human-interface technology companies. A symbiosis between university and industry R&D efforts can lead to the mass production of soft electronics for diverse applications ranging from healthcare to soft robotics that require the unique combination of characteristics such as compliance, safety and comfort that soft electronics can offer. Continued advancement in the field will enable more advanced functionalities to these soft devices to rival their rigid counterparts. This can play a vital role in improving the quality of life and how we interact with people and our surrounding environment.
