Biaxially Stretchable Ultrathin Si Enabled by Serpentine Structures on Prestrained Elastomers

Abstract

most of the materials' intrinsic fracture limit. [1][2][3][4][5] Realized through the combinations of materials, device layouts, and mechanical structure designs, stretchable electronics have a broad range of applications in areas ranging from wearable photo voltaics, to personal health monitors, to sensitive robotic skin prosthetics, to soft surgical tools, and to electronic "eyeball" imaging devices. [6][7][8][9][10] In all of these cases, mechanical stretchability is a key, enabling characteristic. Recent advances in material design and synthesis have led to many stretchable polymeric functional materials such as conductors, [11][12][13] semiconductors, [14,15] mechanophores, [16,17] etc., which provide immediate outlets to stretchable electronics. [13][14][15]18] In particular, from the perspective of electronics performance, among all kinds of stretchable electronics, those employing inorganic materials are especially attractive since they are able to offer a high profile of device performance besides their mechanical merits for applications such as biomedical instruments, where high performance is required.To date, many studies have reported on developing stretchable inorganic semiconductors from materials, such as Si, which are intrinscally brittle. One prevalent strategy is the prestrain strategy, in which very thin stiff films are first bonded or deposited on a prestretched elastomer substrate and then the prestrain on the elastomer is released resulting in simultaneously generated surface microstructures. The prestrain strategy has been successfully adopted to generate stretchable Si-based electronics, which represents a way of exploiting out-of-plane deformation to induce stretchability. [19][20][21][22][23][24][25][26][27] In this case, the stretchability is limited to the prestrain applied on the elastomer substrate; the thin films become flattened when stretched at the same extent of the prestrain, and further stretching will induce fracture. In addition, most of the reported devices were generated by uniaxial prestrains on materials in the configuration of thin films, ribbons, or wires. [19][20][21][22][23][24] Thin films bonded with prestretched elastomer substrate along biaxes give rise to undefined surface topographies depending upon the orders of the prestrain relaxation.The other widely adopted strategy, which lies in constructing devices in the configuration of thin serpentine interconnects with island shaped Si functional electronics, has been explored for stretchable electronics, where in-plane geometries of the thin serpentine wires enable stretchability. [28][29][30] In this case, the stretchability simply depends on the ratio of contour length Building stretchable electronics from inorganic materials is a testified pathway toward devices with high performances for many applications in fields such as optoelectronics, biomedical, etc. Owing to the unstretchable nature of these materials (e.g., brittleness of Si), existing ways to enable stretchabilities mainly involve either bonding thin f...

Soft Electronics for the Skin: From Health Monitors to Human–Machine Interfaces

“…[34] In addition to imparting flexibility to electronic devices, they also require mechanical stretchability to better interface and concurrently deform with the skin. Two strategies have been applied to achieve mechanical stretchability in soft electronics: 1) utilizing intrinsically stretchable, rubbery materials including rubbery electronic materials (semiconductors, conductors, and dielectrics) [14,15,24,[35][36][37][38][39][40][41][42][43][44][45] and liquid metals [46][47][48][49] to build the electronics; 2) employing engineered structures like wrinkles, [34,[50][51][52][53][54][55][56] serpentines, [12,17,33,44,[57][58][59][60][61] island-bridge structures, [62,63] textiles, [64] origami, [65,66] kirigami, [37,67] and microcracks [68] to accommodate the induced strain. [30,…”

Expanding the versatility and functionality of iontronic devices

“…This structure helps in precise control of the electromechanical performance under stretching cycles. The major challenge in these structures is the complicated fabrication [108].…”

Skin‐Like Electronics for Perception and Interaction: Materials, Structural Designs, and Applications

“…Both wrinkle and buckle structures require the release of a pre‐stretch to achieve stretchability. Serpentine [ 25,99,109–111 ] is a planar structure that can be stretchable itself without the need for pre‐strain release. Gonzalez et al [ 99 ] studied different serpentine shapes (i.e., ‘‘U”, half‐circle, elliptical, and ‘‘horseshoe” shapes), and found that the “horseshoe” design induced a high stretchability (i.e., minimum stress concentration).…”