Island Effect in Stretchable Inorganic Electronics

Abstract

microsystem technologies integrated with the human body for health monitoring [8][9][10][11][12][13][14] and disease treating, [15][16][17][18][19][20][21][22][23] to soft systems for low-power radio communication, [24] efficient energy harvesting/ storage, [25][26][27][28] high-capacity memory technologies, [29,30] and seed-inspired electronic micro-fliers. [31,32] An important class of these deformable electronic devices relies on novel structural designs of the device layout and hybrid integration with the soft elastomer substrate to achieve a high elastic stretchability in devices made of inorganic electronic components. [33][34][35][36][37][38][39][40] Herein, the elastic stretchability refers to the value of elongation of the device as elastically stretched to a strain level, below which the device can reversibly return to the load-free state, even after thousands of cycles without material failure, for example, fatigue failure of ductile materials, fracture of brittle materials and delamination at adhesive interfaces. Among various structural designs of stretchable inorganic electronics, [41][42][43][44][45][46][47][48][49][50][51][52][53] the "island-bridge" design represents a widely used strategy, where the bridge-like deformable interconnects in the intermediate regions (i.e., trenches) between the island-like non-stretchable elements (e.g., commercial chips) provide the stretchability, due Island-bridge architectures represent a widely used structural design in stretchable inorganic electronics, where deformable interconnects that form the bridge provide system stretchability, and functional components that reside on the islands undergo negligible deformations. These device systems usually experience a common strain concentration phenomenon, i.e., "island effect", because of the modulus mismatch between the soft elastomer substrate and its on-top rigid components. Such an island effect can significantly raise the surrounding local strain, therefore increasing the risk of material failure for the interconnects in the vicinity of the islands. In this work, a systematic study of such an island effect through combined theoretical analysis, numerical simulations and experimental measurements is presented. To relieve the island effect, a buffer layer strategy is proposed as a generic route to enhanced stretchabilities of deformable interconnects. Both experimental and numerical results illustrate the applicability of this strategy to 2D serpentine and 3D helical interconnects, as evidenced by the increased stretchabilities (e.g., by 1.5 times with a simple buffer layer, and 2 times with a ring buffer layer, both for serpentine interconnects). The application of the patterned buffer layer strategy in a stretchable light emitting diodes system suggests promising potentials for uses in other functional device systems.

Advancements in Electronic Materials and Devices for Stretchable Displays

“…[9,51] The disconnection of interconnects near the edge of the island pixel area due to localized strain can limit the stretchability of the island-bridge structures. [52][53][54] To improve the stretchability of the stretchable display array, various strain engineering approaches that have applied lower Young's modulus materials (Figure 3c), [55] stiff materials with a gradient modulus (Figure 3d), [56][57][58][59][60][61] or pillar structures (Figure 3e) [62] have been reported. In addition, a kirigami-based design for a stretchable display without image distortion was suggested.…”

Skin‐Inspired Porous Mesh Bioelectronics with Built‐In Multifunctionality for Concurrently Monitoring Heart Electrical and Mechanical Functions

“…Besides, the central island is designed for anchoring the hard bioelectronic sensing component (i.e., accelerometer) and is not stretchable, which cannot fit human skin mechanics. [26] Therefore, we add a buffer serpentine region to relieve the island effect; the buffer region is designed with a 225°arc angle with a large critical strain (≈100%); thus, the island effect can be relieved with the buffer region [27] to fit the overall mesh mechanics. Figure 1d indicates that multifunctional porous mesh bioelectronics exhibit high breathability, whose water vapor transmission rate (≈28 mg cm −2 h −1 ) is more than 40 times higher than that (≈0.7 mg cm −2 h −1 ) of the PI film with the same thickness (25 μm thick) and is comparable to that of an open bottle (≈40 mg cm −2 h −1 ).…”

Mechanical Gradients Enable Highly Stretchable Electronics Based on Nanofiber Substrates

“…Various attempts have been devoted to interconnect stretchable circuits with commercial high-performance ICs. For example, interconnecting inorganic semiconductor elements with geometric structures through mechanical design (e.g., island-bridge structures, serpentine interconnects, and wave structures) and then embedding them on elastic substrates is one of the strategies commonly employed in the current research. − Such electronic devices have high performance and integration, but they are not ductile enough (usually within 20%). ,− Moreover, the manufacturing technology is complicated and uneconomical, especially for long-term durable devices . Another popular strategy is to simultaneously encapsulate stretchable or liquid conductive materials (e.g., liquid metals (LM) and conductive inks) and rigid ICs inside elastomers, which can also achieve stretchable connections. − Although this scheme has effectively improved the stretchability of such devices, it introduces challenges from high sealing requirements and unstable interfaces. , On the other hand, the above strategies usually use materials such as polydimethylsiloxane (PDMS), polyimide (PI), and polyethylene terephthalate (PET) as substrates, and their air impermeability and the mismatch of elastic modulus with natural skin can affect the wearer’s comfort. − The researchers are still searching for superior materials and techniques to make stretchable electronics that are safe and comfortable .…”