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Frontiers in Energy

Front Energ    2012, Vol. 6 Issue (4) : 311-340
Direct writing of electronics based on alloy and metal (DREAM) ink: A newly emerging area and its impact on energy, environment and health sciences
Qin ZHANG1, Yi ZHENG1, Jing LIU2()
1. Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China; 2. Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China; Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, China
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Electronics, such as printed circuit board (PCB), transistor, radio frequency identification (RFID), organic light emitting diode (OLED), solar cells, electronic display, lab on a chip (LOC), sensor, actuator, and transducer etc. are playing increasingly important roles in people’s daily life. Conventional fabrication strategy towards integrated circuit (IC), requesting at least six working steps, generally consumes too much energy, material and water, and is not environmentally friendly. During the etching process, a large amount of raw materials have to be abandoned. Besides, lithography and microfabrication are typically carried out in “Cleanroom” which restricts the location of IC fabrication and leads to high production costs. As an alternative, the newly emerging ink-jet printing electronics are gradually shaping modern electronic industry and its related areas, owing to the invention of a series of conductive inks composed of polymer matrix, conductive fillers, solvents and additives. Nevertheless, the currently available methods also encounter some technical troubles due to the low electroconductivity, complex sythesis and sintering process of the inks. As an alternative, a fundamentally different strategy was recently proposed by the authors’ lab towards truly direct writing of electronics through introduction of a new class of conductive inks made of low melting point liquid metal or its alloy. The method has been named as direct writing of electronics based on alloy and metal (DREAM) ink. A series of functional circuits, sensors, electronic elements and devices can thus be easily written on various either soft or rigid substrates in a moment. With more and more technical progresses and fundamental discoveries being kept made along this category, it was found that a new area enabled by the DREAM ink electronics is emerging, which would have tremendous impacts on future energy and environmental sciences. In order to promote the research and development along this direction, the present paper is dedicated to draft a comprehensive picture on the DREAM ink technology by summarizing its most basic features and principles. Some important low melting point metal ink candidates, especially the room temperature liquid metals such as gallium and its alloy, were collected, listed and analyzed. The merits and demerits between conventional printed electronics and the new direct writing methods were comparatively evaluated. Important scientific issues and technical strategies to modify the DREAM ink were suggested and potential application areas were proposed. Further, digestions on the impacts of the new technology among energy, health, and environmental sciences were presented. Meanwhile, some practical challenges, such as security, environment-friendly feature, steady usability, package, etc. were summarized. It is expected that the DREAM ink technology will initiate a series of unconventional applications in modern society, and even enter into peoples’ daily life in the near future.

Keywords direct writing of electronics based on alloy and metal (DREAM) ink      direct writing of electronics      printed electronics      liquid metal ink      integrated circuit      consumer electronics      nano liquid metal     
Corresponding Authors: LIU Jing,   
Issue Date: 05 December 2012
 Cite this article:   
Qin ZHANG,Yi ZHENG,Jing LIU. Direct writing of electronics based on alloy and metal (DREAM) ink: A newly emerging area and its impact on energy, environment and health sciences[J]. Front Energ, 2012, 6(4): 311-340.
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Fig.1  Typical applications of printed electronic inks in life science, aerospace, solar cells, circuits [] and so forth
Fig.2  Differences between printed electronics and conventional IC electronics
Fig.3  Output of several printing cases using different conductive inks
(a) Multiple prints of carboxylated multi-walled carbon nanotube; (b) Canon bt-400 plastic; (c),(d) 80 g/mpaper surfaces; (e) scanned image of a photograph (105 mm×110 mm) printed (×5) on Xerox color copier paper (100 g/m) using the water-based CNT ink []
Fig.4  Inkjet printing
(a) Schematic inkjet-printing process of the ITO nano particle with inset of the picture showing ITO solution jetting; (b) inkjet-printing system for coating of ITO electrode at atmospheric pressure []
Fig.5  Schematic diagrams of an aerosol jet direct writing system and micropen []
Fig.6  Low melting point metals []
Fig.7  Demonstrated wettability of GaIn-based liquid metal inks written on different substrate materials []
(a) Epoxy resin board; (b) glass; (c) plastic; (d) silica gel plate; (e) typing paper; (f) cotton paper; (g) cotton cloth; (h) glass fiber cloth
Fig.8  Optical images of conductive text or patterns written on different substrates by using GaIn-based liquid metal ink
Fig.9  Optical images of LEDs with GaIn-based liquid metal ink as electrical interconnects written on different substrates
Fig.10  Directly writing electrical elements such as resistor, inductor and capacitor on paper to form a functional circuit []
Fig.11  Melting point of Sn-Zn-Ga alloy as a function of the addition of Ga []
Fig.12  Schematic diagram of liquid metal and cooling device
(a)–(d) Liquid metal as thermal interface materials []; (e) enhanced coolant in cooling device []
Fig.13  Viscosity of gallium changes with temperature []
Tab.1  Electrical resistivity of SnSb alloys with different indium content
Fig.14  Atomic structures of GaAs and GaN
Fig.15  Applications of GaAs, GaN as semiconductor
Fig.16  Electromagnetic pump and its working mechanism
Fig.17  Surface tensions () of gallium and indium as functions of temperature by the sessile drop method []
Fig.18  Shear strength of SnAgCuEr alloy as a function of Er content []
AlloysYoung’s modulus E/GPaShear modulus/GPaBulk modulus/GPaLame’s constant/GPa?t,f
Tab.2  Mechanical properties of SnSbIn melt-spun alloys []
Fig.19  Corrosion behavior between 6063 aluminum-alloy and liquid gallium []
Fig.20  Low melting point metals of Ga and eutectic GaIn alloy []
Fig.21  Prototypical structure of gallium trioxide
Fig.22  Gallium dust and transparent hexagonal crystals of GaN
(a) Ammono’s first GaN crystals were tiny, and metallic impurities gave them a brownish tint; (b) after nearly two decades of refinement, Ammono’s growth technique now yields wondrously fine hexagonal crystals up to 2 inches across []
Fig.23  Schematic diagram of consumption in conventional electronics
Fig.24  Differences between subtractive and additive technologies []
Fig.25  Environmental pollutions of traditional integrated circuits
Fig.26  Some emerging applications []
Fig.27  Schematic diagrams of application issues
Fig.28  Application of liquid metals from local to surface
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