KOSEN 한인과학기술자네트워크

• Solution Growth 

 A high degree of control over the size, structure, and composition of nanocrystals is essential to tune their chemical and physical properties for target applications. In particular, 2D nanocrystals of different sizes have been investigated extensively owing to their superior electrical, optical, and  thermal properties.  In reaction system, precursor, surfactant, reductant determines the final shape of synthesized materials due to different surface energies of different crystallographic planes.

  We aim to control the structure of synthesized materials by controlling reaction environment.

 

• Stretchable Conductor

 Stretchable electronics are having great interests because of their wide availability in wearable devices, soft robotics, and implants. For the stretchable electronics, one of the most important and fundamental components is stretchable conductor. Stretchable conductor must maintain their original mechanical, and electrical performance despite of the stretching cycles. Our lab research aims the development of structural, and intrinsically stretchable conducting materials as a basic component for stretchable electronics for the actual use of display, transistor, sensors, and batteries. The materials include metallic hybrid materials which are composed of 0-D, 1-D, 2-D nanomaterials and stretchable polymer, in addition, organic conductive material such as PEODT:PSS.

Ag nanoparticle-SBS composite fiber mat

PEDOT:PSS dough

Au nanosheet composite

Nat. Nanotechnol. 2012, 7, 803-809

ACS Appl. Mater. Interfaces 2017, 9, 44096-44105

Adv. Mater., 2016, 28, 4455-4461

• Stretchable Electroluminescent & Electrochemical System

  As interest in human-friendly devices grows, interest in the development of displays that enable visual communication between electronic skin system and human is also increasing. In addition, there are growing demands for new displays that require folding/stretchability, such as curved lighting, various forms of the Internet of Things (IoT) displays, and electronic skins.

 Our lab designs stretchable display systems such as alternating current electroluminescent (ACEL), and light-emitting electrochemical (LEC) devices, through various materials and structural approaches.

Light-emitting electrochemical (LEC)

Stretchable LEC

Alternating current electroluminescent (ACEL)

• Stretchable Strain Sensor

 Mechanical monitoring of our body is an emerging requirement for next generation human-friendly electronics, which can measure not only tiny bio-signals such as wrist pulse, apexcardiogram and facial expression, but large motions like joint and muscle motions. Strain sensing is a basic function of the sensor system and the physical intimacy could be acquired with softness or stretchability of the materials comprising sensors. We are developing the stretchable conducting materials based on 0-D, 1-D, 2-D nanomaterials with chemical and physical elastomer (block-copolymer) for strain sensor application.

Fibril structured deposited gold film

Adv. Mater., 2018, 30, 1801408

ACS Appl. Mater. Interfaces, 2018, 10, 40141-40148

2-D percolation based Heart monitoring device

Adv. Mater., 2016, 28, 6359-6364

• Tactile Sensor

 Tactile sensing is the most important function comprising electronic skin system. As a substitute for mechanoreceptor in human skin, it feels external mechanical stimulation like pressure and strain and transduces to electrical signals. Film type high sensitive pressure sensor has been used to measure small bio-signals. In our lab, we are fabricating various type of pressure sensor matrix array for different purpose. On-skin sensors measured pressure profiles in small scale like human cutaneous system, that were utilized as Braille scanner and also showed potentials for prosthetics or robot skin application. Additionally, we are also interested in active tactile sensors using self-power generating system.

Conductive Microparticle based pressure sensor array

Adv. Funct. Mater., 2018, 28, 1801858

Active tactile sensing with Triboelectricity

Nano energy, 2019, 56, 347

• Bioelectrical Signal Sensor

 Recently, people want to take care their health condition in real time. There are electrical signals from our body such as electrocardiogram, electroencephalogram…etc. These signals help us to diagnose health condition of our body. Mobile healthcare devices want to measure these electrical signals. To measure these signals, it is important to have conformal contact between the sensor and the skin. Because skin shows dynamic movement, this sensor should be stretchable. The device also should have breathability and make sweat evaporate easily for long-term use. All materials in the sensor must be biocompatible and robust. In our lab, bioelectrical signal sensors are fabricated using hydrogels, conductive polymers and nanoparticles. In the future, we will develop this research from on-skin wearable sensors to implantable sensors.

Breathable electrocardiogram sensor

• Microparticle assembly

 Microparticle assembly has an effective meaning to the both research and industrial field. Via simple rubbing process, microscale-powders can easily form high crystallinity of monolayer over large area. This assembly has special optical properties, such as photonic crystal. The reflected light color varies depending on the crystal orientation of the particle assembly. In addition, the position registry and the deformability are guaranteed with the physical/ chemical patterning on the substrate. Due to these things the microparticle assembly can be suggested as one of the methodologies of the stretchable devices that are being actively developed by the electronics companies around the world.

Position-registered Microparticle assembly 

ACS Appl. Mater. Interfaces, 2016, 8, 28149-28158

Adv. Mater., 2014, 26, 4633-4638

• Patterning process development

 Patterning process is a crucial technology for device fabrication and is used in a variety way as well. Integrating circuit for stretchable electronics requires reliable and efficient patterning process, so in our lab, we are developing nozzle printing and screen printing process with conductive ink. Controlling characteristics of the ink solution is a key for the process development. Additionally, we produce partterns by capillary force lithography, nano-imprinting, and photolithography, etc. Furthermore, we can use assembled particle monolayer for patterning masks.

Nozzle printing of metal precursor

Microfabrication of PDMS pillar

Microimprint of viscoelastic PEDOT:PSS