Tunnel Encapsulation Technology for Durability Improvement in Stretchable Electronics Fabrication

Abstract

Great diversity of process technologies and materials have been developed around stretchable electronics. A subset of them, which are made up of zigzag metal foil and soft silicon polymers, show advantages of being easy to manufacture and low cost. However, most of the circuits lack durability due to stress concentration of interconnects entirely embedded in elastic polymer silicone such as polydimethylsiloxane (PDMS). In our demonstration, tunnel encapsulation technology was introduced to relieve stress of these conductors when they were stretched to deform in and out of plane. It was realized by dissolving the medium of Polyvinyl Alcohol (PVA), previous cured together with circuits in polymer, to form the micro-tunnel which not only guarantee the stretchability of interconnect, but also help to improve the durability. With the protection of tunnel, the serpentine could stably maintain the designed shape and electrical performance after 50% strain cycling over 20,000 times. Finally, different materials for encapsulation were employed to provide promising options for applications in portable biomedical devices which demand duplicate distortion.

Long wavy copper stretchable interconnects fabricated by continuous microcorrugation process for wearable applications

“…8,9,21,22 Fifth, a horizontal spring-like structure of metal interconnects has been constructed by lithography and etching processes. [23][24][25][26][27][28][29] These horseshoe-patterned interconnects have the advantage of high conductivity and stretchability, but require large surface areas for one electrode. The length of the electrode is limited up to 20 cm because the houseshoe-pattern is constructed by micromachining tools such as mask aligners and sputters which are developed for 8-in.…”

“…Since the cracked film can deflect and twist out of plane, tribranched microcracks of thin metal film can sustain up to 30% stretch but the length of the microcrack electrode is limited up to 20 cm which is determined by the size of vacuum chamber of metal sputter . Fifth, a horizontal spring‐like structure of metal interconnects has been constructed by lithography and etching processes . These horseshoe‐patterned interconnects have the advantage of high conductivity and stretchability, but require large surface areas for one electrode.…”

Fluid Microchannel Encapsulation to Improve the Stretchability of Flexible Electronics

“…Xu [53] provided a liquid encapsulation (LE) method to resolve the stretchability limitation, but it also has drawbacks in that a vast volume of liquid introduces leakage as a possible failure mode and free-floating electronic components can result in a risk of short circuits. Leng [54] presented a tunnel encapsulation method to improve the device stretchability, but it would become hardly operable when being applied in ultrasmall device encapsulation, owing to the poor dissolving effect on the Recently, stretchable inorganic electronic devices are rapidly developed, comprising emerging design strategies and fabrication techniques for assembling high-performance electronic components in slight, soft, and flexible forms, with broad medical and industrial applications. Although reliable encapsulation plays an indispensable role in offering physical and chemical protection for flexible devices, there are relatively few studies on flexible encapsulation, and conventional encapsulation methods still suffer from low stretchability.…”

Editorial for Special Issue on Flexible Electronics: Fabrication and Ubiquitous Integration

“…There are 10 papers published in this Special Issue, covering new strategies for a paradigm shift in the design [ 1 , 2 , 3 ], fabrication [ 4 , 5 , 6 , 7 ], and encapsulation [ 8 , 9 , 10 ] of next-generation flexible systems. Xiao et al [ 1 ] proposed an “island-bridge” strategy to design high-performance stretchable electronics composed of inorganic rigid components so that that can they can be conformally transferred to non-developable surfaces.…”

“…These intrinsically soft circuits can easily match the mechanical impedance of biological tissue and brings significant opportunities for innovation in modern bioelectronics and electrical engineering. A “tunnel encapsulation” strategy is proposed by Leng et al [ 8 ] in order to avoid the typical lack of durability due to stress concentration of flexible interconnects entirely embedded in elastic polymer silicones, such as polydimethylsiloxane (PDMS).…”