Abstract
This article presents an overview on typical properties, technologies, and applications of liquid metal based flexible printed electronics. The core manufacturing material—room-temperature liquid metal, currently mainly represented by gallium and its alloys with the properties of excellent resistivity, enormous bendability, low adhesion, and large surface tension, was focused on in particular. In addition, a series of recently developed printing technologies spanning from personal electronic circuit printing (direct painting or writing, mechanical system printing, mask layer based printing, high-resolution nanoimprinting, etc.) to 3D room temperature liquid metal printing is comprehensively reviewed. Applications of these planar or three-dimensional printing technologies and the related liquid metal alloy inks in making flexible electronics, such as electronical components, health care sensors, and other functional devices were discussed. The significantly different adhesions of liquid metal inks on various substrates under different oxidation degrees, weakness of circuits, difficulty of fabricating high-accuracy devices, and low rate of good product—all of which are challenges faced by current liquid metal flexible printed electronics—are discussed. Prospects for liquid metal flexible printed electronics to develop ending user electronics and more extensive applications in the future are given.
Highlights
Printed electronics is the technology to fabricate electronic devices based on the principle of printing [1]
Classical flexible electronics refers to the technology by which organic/inorganic electronic devices are deposited on a flexible substrate to form a circuit [3]
The rigid circuit board can protect the electronic components from being damaged, it restricts the ductility and flexibility of the electronics. With intriguing properties such as softness, ductility, and low-cost fabrication, flexible electronics has broad application prospects in the information, energy, medicine, and defense technology fields through providing smart sensors, actuators, flexible displays, organic light-emitting diodes (OLEDs), and so on
Summary
Printed electronics is the technology to fabricate electronic devices based on the principle of printing [1]. The most obvious characteristic of flexible electronics lies in their flexibility compared with traditional rigid microelectronics, which makes them stretchable, conformal, portable, wearable, and easy to print quickly [4,5,6,7,8] Because of their unique merits in terms of electrical, printable, biomedical, and sensing properties, flexible electronics can find diverse applications in electronic components [9], printing technology, implantable devices [10], and health monitors [11], with specific uses such as antennas [12], eyeball cameras [13] and pressure sensors [14], etc. Micromachines 2016, 7, 206 on skin substrates as physiological testing devices via liquid metal spraying and pre-designed mask; published by Journal of Mterials Chemistry B, 2014.); Liquid metal tag on human skin [56] (Reproduced with permission from Jeong, S.H.; Wu, Z. et al, Liquid alloy printing of microfluidic stretchable electronics; published by Lab on a Chip, 2012.); ECG test by liquid metal electrode [57] (Reproduced with permission from Yu, Y.; Zhang, J.; Liu, J., Biomedical implementation of liquid metal ink as drawable ECG electrode and skin circuit; published by PLoS ONE, 2013.); “Wearable bioelectronics”: Liquid metal wristband [58] (Reproduced with permission from Wang, Q.; Yu, Y.; Yang, J.; Liu, J., Fast fabrication of flexible functional circuits based on liquid metal dual-trans printing; published by Advanced Material, 2015.); A wearable data glove [59] (Reproduced with permission from Matsuzaki, R.; Tabayashi, K., Highly stretchable, global, and distributed local strain sensing line using gainsn electrodes for wearable electronics; published by Advanced Functional Material, 2015.); Footwear-embedded microfluidic energy harvest [60] (Reproduced with permission from Krupenkin, T.; Taylor, J.A., Reverse electrowetting as a new approach to high-power energy harvesting; published by Nature Communication, 2011.)
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