, Volume 6, Issue 4, pp 311-340
Date: 12 Nov 2012

Direct writing of electronics based on alloy and metal (DREAM) ink: A newly emerging area and its impact on energy, environment and health sciences

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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.

Dr. Jing Liu is a professor with the Department of Biomedical Engineering of Tsinghua University (THU) and the Technical Institute of Physics and Chemistry, Chinese Academy of Sciences (CAS). He received his B.E. degree in Power Engineering and Control and B.S. degree in Physics in 1992, and Ph.D. in Thermal Science in 1996 from THU. He then served as assistant professor at THU, a postdoctoral research associate at Purdue University, and a senior visiting scholar at Massachusetts Institute of Technology. He has been a professor with the CAS since July 1999 and a professor with THU since August 2008. Dr. Liu has authored nine popular books on cutting edge frontiers in energy and bioengineering areas (among which Micro/Nano Scale Heat Transfer has been reprinted five times), fourteen invited book chapters, over three hundred peer reviewed journal papers, and about seventy international conference presentations or invited lectures. He holds more than 100 patents.
Prof. Liu’s research interests include microenergy, mobile health technology, thermal management, bioheat and mass transfer, and micro/nano fluidics. He contributed significantly to the bioheat transfer area through numerous conceptual innovation, methodology development and technical inventions and is a world-renowned expert in this area. His work is also fully reflected in energy and related areas, where he pioneered a series of non-conventional technologies especially the liquid metal based thermal management, waste heat recovery, electricity generation and direct writing electronics etc. Dr. Liu is a recipient of 2010-2011 Best Paper of the Year Award from ASME Journal of Electronic Packaging, the National Science Fund for Distinguished Young Scholars of China, National Science and Technology Award for Chinese Young Scientist, Mao Yi-Sheng Science and Technology Award for Beijing Youth, and five times highest teaching award from CAS etc.