Design Criteria for Horseshoe and Spiral‐Based Interconnects for Highly Stretchable Electronic Devices

Abstract

Stretchable electronics can be used for numerous advanced applications such as soft and wearable actuators, sensors, bio‐implantable devices, and surgical tools because of their ability to conform to curvilinear surfaces, including human skin. The efficacy of these devices depends on the development of stretchable geometries such as interconnection‐based configurations and the associated mechanics that helps to achieve optimum configurations. This work presents the essential mechanics of silicon (Si) island‐interconnection structures, which include horseshoe and spiral interconnections, without reducing the areal efficiency. In particular, this study demonstrates the range of the geometrical parameters where they have a high stretchability and cyclic life. The numerical results predict the areas that are prone to breaking followed by experimental validation. The figure‐of‐merit for these configurations is achieved by mapping the fracture‐free zones for in‐plane and out‐of‐plane stretching with essential implications in stretchable and wearable system design. Furthermore, this work demonstrates the mechanical response for a range of materials (i.e., copper, gold, aluminum, silver, and graphene) that experience the plastic deformations in contrast to conventionally used Si‐based devices that represent the extended usage for advanced stretchable electronic devices. The detailed mechanics of these configurations provides comprehensive guidelines to manufacture wearable and stretchable electronic devices.

Geometrically engineered rigid island array for stretchable electronics capable of withstanding various deformation modes

“…Previously, rigid islands and various serpentine electrodes have been used to integrate conventional rigid components into stretchable electronics ( 10 , 11 , 23 ). Serpentine electrodes are vulnerable to repetitive deformation because of weak interface with the polymer matrix and due to its intrinsic brittleness.…”

“…Until now, the shapes of rigid islands have been determined according to the specific applications (table S1). In the case of stretchable display or sensor array, since the device arrangement is a square packing, the square-shaped islands (9,10,14,(20)(21)(22)(23)(24)(25) have been mainly used. On the other hand, in the stretchable battery, hexagon- (23,26,27) or circle-shaped islands (CIs) (11,(28)(29)(30) have been used to increase the density of the unit cell.…”

“…In the case of stretchable display or sensor array, since the device arrangement is a square packing, the square-shaped islands (9,10,14,(20)(21)(22)(23)(24)(25) have been mainly used. On the other hand, in the stretchable battery, hexagon- (23,26,27) or circle-shaped islands (CIs) (11,(28)(29)(30) have been used to increase the density of the unit cell. However, since these islands are vulnerable to interfacial crack propagation, we geometrically engineered the islands that are effective in suppressing crack propagation.…”

Mechanical reliability of self-similar serpentine interconnect for fracture-free stretchable electronic devices

“…It is well-known that Si experiences mechanical failure as long as its principal strain (ε p ) exceeds 1%. 36,[46][47][48] During its functioning, stress concentration in the SS-interconnect may result in ε p higher than 1%, defining the fracture state or conditions in this work.…”

Transparent Omni‐Directional Stretchable Circuit Lines Made by a Junction‐Free Grid of Expandable Au Lines

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requirements should be met in stretchable circuit boards; patternability, high conductivity, and electrical invariance under large deformation in any direction.Direct metal deposition was successfully used to obtain non-transparent stretchable circuit lines through the structural approaches such as the wrinkle formation and the horse-shoe shape. [29][30][31][32] The prestrain approach is limited in pattern resolution and difficult produce the circuit line patterns in desired shapes at target positions because the metal pattern is deformed unevenly. In addition, the out-of-plane buckling makes it difficult to incorporate additional layers or devices on the circuit lines.

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