Research Team Led by SNU Professor Kauh Sang Ken Develops a Liquid Metal Circuit that Can Be Bent, Stretched, and Folded

- Expects Application into Flexible and Wearable Devices
- Selected as Cover Article of Advanced Functional Materials


▲ Department of Mechanical and Aerospace Engineering Professor Kauh Sang Ken (Left), PhD Candidate Kim Doyoon (Right)

 
SNU College of Engineering (Dean Cha Kook-Heon) announces on 18^th that Professor Kauh Sang Ken (Department of Mechanical and Aerospace Engineering) and PhD candidate Kim Doyoon’s research team has developed a technology to build liquid metal circuit with microscale line width. The liquid metal circuit and sensor built from the team’s new technology are bendable, foldable, and stretchable and can maintain their electrical conductivity without having any of their wires to snap.
 
Recently, there is a growing interest in flexible and wearable devices; thus, naturally researchers are carrying out active studies on flexible circuits. Graphene and carbon nanotubes, which are both conductive and flexible, are two electrospun fibers that are drawing majority’s attention. However, both materials are vulnerable against heat and require overly-complex manufacturing processes for mass production.
 
Therefore, as an alternative for electrospun fibers, printing and patterning methods using liquid metals like gallium compounds are being developed. Yet, gallium compounds too have one serious limitation; due to its surface tension, manufacturing in microscale is difficult and is only printable on flat surfaces.
 
Hence, Professor Kauh’s team designs a system that allows printing on curved and inclined surfaces. By adopting the liquid metal direct injection method and liquid metal transportation method based on its phase change, the team has succeeded in reducing the width of circuit to microscale.
 
The production process of this liquid metal circuit involves first printing liquid metal to a line width of 100 micrometers, then stretching and carrying it to the next board repetitively for 6-7 times to finally earn a finished product of 2 micrometers width. Kauh’s team explains that if the first print is reduced to 20 micrometers, just 2-3 cycles of stretching can achieve the targeted 2-micrometers circuit.
 
Kauh’s team is the first to abandon the conventional method of filling the elastic circuit mold with liquid metal and directly making the microscale liquid metal circuit. The circuit and sensor developed in this manner maintains their electrical conductivity without having their wires broken when external forces like a stretch or a bend are applied.
 
Professor Kauh states, “We have produced a liquid metal pattern of 2 micrometers width without mold through our special liquid metal printing and phase change patterning methods. We anticipate the application of these new techniques to various fields including flexible display and sensor and wearable devices.”
 
The research findings have been published on a materials science journal Advanced Functional Materials as its cover research of June 9^th issue under the title of “Towards Sub-Microscale Liquid Metal Patterns: Cascade Phase Change Mediated Pick-n-Place Transfer of Liquid Metals Printed and Stretched over a Flexible Substrate.”
 
This study has been conducted with the support of the Individual Basic Science & Engineering Research Program of the Ministry of Science, ICT and Future Planning and the National Research Foundation of Korea.
 
[Inquiries]
Kim Doyoon, PhD Candidate, Department of Mechanical and Aerospace Engineering (First Author) / 010-7331-2760 / doyoon86@gmail.com
Lee Dongha, Manager, Office of International Affairs, College of Engineering, SNU / 02-880-9148 / 010-8249-2174 / lee496@snu.ac.kr
 
[Reference Links]
1. Research Paper: Doyoon Kim, Young Yoon, Jungchul Lee, Sang Ken Kauh “Towards Sub‐Microscale Liquid Metal Patterns: Cascade Phase Change Mediated Pick‐n‐Place Transfer of Liquid Metals Printed and Stretched over a Flexible Substrate“(https://doi.org/10.1002/adfm.201800380)
 
2. Cover Page of Advanced Functional Materials: Flexible Electronics: Towards Sub‐Microscale Liquid Metal Patterns: Cascade Phase Change Mediated Pick‐n‐Place Transfer of Liquid Metals Printed and Stretched over a Flexible Substrate (Adv. Funct. Mater. 28/2018) Doyoon Kim, Young Yoon, Jungchul Lee, Sang Ken Kauh, First published: 09 july 2018 (https://doi.org/10.1002/adfm.201870195)

 

▲ The Liquid Metal Circuit on the Cover Page of Advanced Functional Materials



▲ Mimetic Diagram of Microscale Liquid Metal Patterning