The formation of three-dimensional (3D) interconnections is essential in integrated circuit packaging technology. However, conventional interconnection methods, including the wire-bonding process, were developed for rigid structures of electronic devices, and they are not applicable to the integration of soft and stretchable electronic devices. Hence, there is a strong demand for 3D interconnection technology that is applicable to soft, stretchable electronic devices. Herein, we introduce the material and the processing required for stretchable 3D interconnections on the soft forms of devices and substrates with high resolutions. Liquid-metal-based composites for use as stretchable interconnection materials were developed by uniformly dispersing Pt-decorated carbon nanotubes in a liquid metal matrix. The inclusion of carbon nanotubes in the liquid metal improves the mechanical strength of the composite, thereby overcoming the limitation of the liquid metal that has a low mechanical strength. The composites can be 3D printed with various dimensions: the minimum diameters are about 5 μm and have a breakdown current density comparable to that of metal wires.

Tactile pressure sensors as flexible bioelectronic devices have been regarded as the key component for recently emerging applications in electronic skins, health-monitoring devices, or human–machine interfaces. However, their narrow range of sensible pressure and their difficulty in forming high integrations represent major limitations for various potential applications. Herein, we report fully integrated, active-matrix arrays of pressure-sensitive MoS2 transistors with mechanoluminescent layers and air dielectrics for wide detectable range from footsteps to cellular motions. The inclusion of mechanoluminescent materials as well as air spaces can increase the sensitivity significantly over entire pressure regimes. In addition, the high integration capability of these active-matrix sensory circuitries can enhance their spatial resolution to the level sufficient to analyze the pressure distribution in a single cardiomyocyte. We envision that these wide-range pressure sensors will provide a new strategy toward next-generation electronics at biomachine interfaces to monitor various mechanical and biological phenomena at single-cell resolution.

Recent approaches in self-healable electrodes use polymers with exhibiting significantly low electrical conductivity, compared to conventional metals. Such self-healable electrodes also require external stimuli to initiate self-healing, or present slow restoration for their intrinsic healing. Herein, we introduce an instantaneous and repeatable self-healing of highly conductive, fully metallic electrodes at ambient conditions. These electrodes consist of silver and liquid metal (with no polymer), and exhibit a sufficiently high conductivity of 2 S/μm. The liquid metal (LM) component enables instantaneous and repeatable self-healing of these electrodes (within a few milliseconds) under no external energy as well as high stretchability. Additionally, the inclusion of silver in this LM improves the mechanical strength of this composite, thereby overcoming the limitation of a pristine LM that has low mechanical strength. Moreover, this composite formation can be effective in preventing the penetration of gallium atoms into different metals, while preserving electrical contact properties. Also the self-healable nature of electrodes enables their outstanding sustainability against electrical breakdown at relatively high electric fields. Furthermore, the compatibility of these self-healable electrodes with conventional photolithography and wet etching facilitates high-resolution patterning for device fabrications, as demonstrated in an example with a self-healable organic light-emitting diode display.