Industrial Electronics

Overview of stretchable circuit technology

16 June 2021
Stretchable insulating resin film with electronic circuit. Source: Panasonic

Stretchable and flexible circuits represent a relatively modern technology that is achieving a wide range of uses thanks to their components' ability to be bent, twisted and adapted to complex non-planar surfaces. At the moment, wearable electronics systems support these circuits, resulting in several uses in the energy, healthcare and military sectors. The surge in demand for smart, wearable and integrated electronics systems over the last decade has attracted attention to the manufacturing techniques for stretchable electronics. As a result, considerable effort has been made to achieve stretchability of electronic devices and to lower the overall manufacturing expense by novel product configurations and advanced material design.

Stretchable circuits are also fulfilling the demands for bio-inspired products or products that need close contact with the human body, as they need curved forms or elastic responses to significant strain distortions. Therefore, mechanical compliance, on the other hand, is important in the manufacturing of stretchable devices, and electronic devices must not sustain a physical injury or degrade in functionality when bent or stretched.

Fabrication methods

Numerous techniques are being used to produce stretchable electronic products, including directly using inherently stretchable materials or making design structures using wavy structure configurations, mesh structures, island-interconnect configurations, origami and kirigami structural shapes, and fractal modeling approaches. Let’s begin with the most widely used method of directly using inherently stretchable materials. For example, stretchable elastomers that can reversibly withstand extreme curvatures are commonly used as soft substrates in a wide range of electronic devices such as thermoplastic polyurethane, styrene-butadiene rubber and natural rubber.

Stretchable electrodes and conductors are deformable, compliant and have stretchable properties that have challenged the conventional wisdom that people would use rigid silicon-based electronics and paved the way for next-generation versatile electronics. Knowledge of nanoscale phenomena, practical components and materials, and soft sensors has advanced to the point that significant advancements in stretchable circuit applications are possible. Another difficulty in fabricating stretchable electronic products is how to design the stretchable conductors, particularly when utilizing the direct printing method.

The likelihood of stretchable conductors has been demonstrated in several experiments over the last few years, culminating in the production of more complex and sophisticated stretchable electronic products. Additionally, by incorporating translucent properties into stretchable products, new applications such as transparent and stretchable electronic devices and stretchable transparent electrodes will be feasible, in which increased amounts of stretchability and optical clarity are needed for conformal positioning of devices on the body or other arbitrary areas.

Nevertheless, this approach of directly using inherently stretchable materials frequently ends in electronic devices with high electrical resistivity and low electrical mobility. As a result, additional techniques such as wavy structure configurations, mesh structures, island-interconnect configurations, origami and kirigami structural shapes, and fractal modeling have been built to develop stretchable systems. These techniques may be used to either increase the tensile strength of inherently stretchable conductors or to permit the use of conductive metals in stretchable electronic products. Moreover, the manufacturing cost is a key element in designing and commercializing stretchable devices.

To get stretchable conductors, the conductive carbon nanomaterials, metal nanowires and polymers are commonly used as fillers and organized in an elastomer matrix in combination with structural designs such as fractal design, island-interconnect and wavy structural configurations. Even so, a stretch factor of greater than 25% is appropriate for use in wearable technology applications and smart clothing. For manufacturing stretchable electronic products, each part of a stretchable electronic system must sustain its output up to a critical strain. Visual transparency can greatly improve the benefits of stretchable practical materials and associated technique improvements, thus facilitating the deployment of stretchable electronics.

Stretchable power sources

The power supply is critical in the development of self-contained stretchable electronic devices. Though many techniques for stretchable electrodes and conductors are available, a vital technological challenge is developing soft power sources with comparable mechanical efficiency that can be used in combination with other stretchable electronic products. Therefore, the development of sophisticated stretchable storage systems and power sources has sparked interest in recent years. Two techniques are often used to make power storage devices with stretchable properties: one is to directly use intrinsically stretchable physical materials, and the other is to utilize the above-mentioned structural technologies capable of operating under mechanical pressure. Major research progress has resulted in stretchable power sources and storage systems such as stretchable nanogenerators, stretchable solar cells and stretchable supercapacitors.

Conclusion

In short, stretchable electronics provide a solid base for applications utilizing popular versatile electronic methods due to their strong integration capabilities with stretchable functional materials and wavy surfaces. The world of wearable electronic devices has been shaped by rapid growth and significant accomplishment, culminating in a persistent need for stretchable electronic devices and stretchable conductors. Recent advancements in stretchable electronics have resulted in the advent of novel innovations, and significant effort has been made to enhance their electronic efficiency under stretching and to imbue the surfaces of different soft substrates with intelligent functions. Even so, comfortable and folding stretchable circuits are incomplete without a soft stretchable energy source that exactly complies with the power requirements of the stretchable electronic product.

To contact the author of this article, email engineering360editors@globalspec.com


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