In‐Plane Deformation Mechanics for Highly Stretchable Electronics

Abstract

Stretchable electronics represents a relatively recent class of technology [1,2] of interest partly due to its potential for applications in sensory robotic skins, [3,4] conformal photovoltaic modules, [5,6] wearable communication devices, [7,8] skin-mounted monitors of physiological health, [9][10][11] advanced, soft surgical and clinical diagnostic tools, [11,12] and bioinspired digital cameras. [13,14] A key challenge in each of these systems is in the development of strategies in mechanics that simultaneously allow large levels of elastic stretchability and high areal coverages of active devices built with materials that are themselves not stretchable (e.g., conventional metals) and are, in some cases, highly brittle (e.g., inorganic semiconductors). For design approaches that embed stretchability in interconnect structures that join rigid device islands, the system level stretchability ε system is much smaller than the interconnect stretchability ε interconnect . Zhang et al. [15] identified the following relationship between the interconnect and system stretchability:, where f dev = (area of active device components)/(total area of the system) is the areal coverage ratio of active device components. Structure designs for stretchable interconnects have evolved from straight [13,16] to curvilinear interconnects, [17] from those bonded to or embedded in the supporting substrate [11,18] to free-standing designs housed in microfluidic enclosures, [19] and from simple structures [17] to fractal/self-similar designs. [15,[20][21][22] All such cases, including a broad variety of shapes, sizes, and geometric arrangements, share the same underlying mechanisms, i.e., out-of-plane buckling of thin structures (metals, insulators, or semiconductors with thickness typically between ≈100 nm and ≈1 µm) provides the basis for elastic stretchability. The most advanced interconnects achieve elastic (reversible)

Buckling analysis in stretchable electronics

“…Recently, Su et al 42 introduced a different route to stretchable structures, where thick bar geometries replace thin ribbon layouts, to yield scissor-like deformations instead of in-plane or out-ofplane buckling modes. In their systematic theoretical, numerical, and experimental studies, it was observed that three different buckling modes exist for serpentine interconnects consisting of both straight and curved segments, as the thickness of interconnects increases from tens of nanometers to~100 μm.…”

“…With optimum designs, the scissoring mechanism can be exploited to increase elastic stretchability (defined as maximum cyclic stretching level that does not cause fracture) to~350%, which represents a sixfold enhancement than previously reported values (about 60%). 43 Su et al 42 analyzed the three buckling modes from the energy perspectives, and obtained analytically the criteria to separate the three different buckling modes:…”

Programmable Hierarchical Kirigami

“…The ability to program the mechanical response of materials and structures is enabling a wide set of innovative applications ranging from stretchable electronics and wearable devices [1,2] to soft robots [3][4][5][6][7] and drug delivery systems. [8,9] Recently, kirigami-the Japanese art of paper cutting-has been identified as a powerful tool to realize programmable mechanical metamaterials.…”

Elastic instability induced mechano-responsive luminescence for super-flexible strain sensing

“…Conventional flexible electronics are bendable devices where the substrate has a reduced thicknesses, laminated with metal interconnects to reduce the strain change due to bending. For the emerging stretchable/super-flexible devices [1][2][3][4], substrate deformation strain could be much higher than the fracture strains of rigid materials during compressing and stretching. To avoid compromising local features such as metal interconnects and integrated transducers, different strategies have been developed, such as island-bridge and serpentine shaped interconnects [1,5] and competing growth of elastic instabilities [4,6].…”

“…Bendable and stretchable sensor and actuator technologies based on soft functional materials have become ever popular with emerging applications such as epidermal electronics, artificial skins, and soft robotics [1][2][3][4]. Conventional flexible electronics are bendable devices where the substrate has a reduced thicknesses, laminated with metal interconnects to reduce the strain change due to bending.…”