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Recent progress in engineering approaches for stretchable electronics and electronic components, including strategies focused on materials science or structural engineering, offer high signal-to-noise detection of vital signs via systems that provide conformal, noninvasive contact to curvilinear skin and are unobtrusive during human activity, such as general motion, exercise, and respiration. Structural engineering strategies with flexible thin films, whose deformation can be categorized as two-dimensional (2D) in-plane or three-dimensional (3D) out-of-plane, provide a release of stress created by stretching, bending, or twisting. Beyond 2D in-plane structural engineering techniques, 3D out-of-plane structural engineering techniques effectively distribute nonlinear and multidirectional 3D strain. Here, we review recent advances in 3D out-of-plane engineering techniques, including wavy and wrinkled structures, pop-up structures, kirigami and origami structures, and nature-inspired structures, and describe the strain distribution mechanisms, fabrication processes, applications, and characteristics of these approaches. We conclude with perspectives on applications of stretchable electronic devices with multidirectional stretchability and the existing challenges for future research.

The electroplating of the gate electrode on a flexible polyimide (PI) substrate was successfully applied to the fabrication of inverted-staggered poly(3-hexylthiophene) (P3HT) organic thin film transistors (OTFTs). The Ni gate electrode was electroplated through patterned negative photo-resist (KMPR) masks onto Cu (seed)/Cr (adhesion) layers that had been sputter-deposited on O 2 -plasma-treated PI substrates. The electrical measurements of the fabricated OTFTs with the SiO 2 gate insulator indicated non-ideal output characteristics, which are similar to the model of electrical transport by a space-charge limited current (SCLC). The use of a poly(4-vinyl phenol) (PVP) and SiO 2 /PVP bilayer gate dielectric produced output characteristics that were closer to the ideal TFT behavior but led to a lower effective mobility and on / off current ( I on / I off ).

The electroplating of source–drain (S/D) electrodes on a flexible polyimide (PI) substrate was applied to the fabrication of staggered poly(3-hexylthiophene) (P3HT) organic thin film transistors (OTFTs). Au or Au/Ni bilayer S/D electrodes were additively electroplated into patterned SU-8 photoresist masks on Cu(seed)/Cr(adhesion) layers sputter-deposited on O 2 -plasma-treated PI substrates. The electrical measurements of the fabricated OTFTs showed that their non-ideal output characteristics were similar to those predicted by the model of electrical transport by the space-charge limited current (SCLC), regardless of the surface preparations used for the Au S/D electrodes.

An effective modeling and simulation schemes of a resistive type Superconducting Fault Current Limiter (SFCL) and DC reactor type SFCL using PSCADIEMTDC are proposed in this paper. In case of resistive type SFCL, current limiting is implemented by the ultra-fast transition characteristics from the superconducting (non-resistive) state to the normal (resistive) state by overstepping the critical current density. The states can generally be divided into three sub-states: the superconducting state, the quench state and the recovery state, respectively. In case of DC reactor type SFCL, it is composed of a superconducting coil and a diode bridge through which AC line current is rectified, and the increase in fault current is limited by the inductance of a superconducting coil. An actual experiment based component model of the real resistive type SFCL is developed and applied for the simulation. The proposed modeling and simulation schemes can be implemented to the grid system readily under various system conditions including sort of faults and the system capacity as well. The simulation results demonstrate the effectiveness of the proposed model and simulation schemes.