Dr. Ji-Hyeon Song

Post-doctoral research associate

Seoul National University

For the past 10 years, Ji-Hyeon Song has been studying mechanical engineering as a student. She recently received her joint Seoul National University and Georgia Technology Ph.D. in May 2019. She is now working as a post-doctoral research associate at Seoul National University.

Her research areas are in micro/nanoscale manufacturing process design. The title of her Ph.D. dissertation is "A dissertation is “A Nanoparticle Laser Patterning Process to Fabricate Flexible Electronics”. She has acquired a unique set of knowledge and skills in the domain of micro/nanofabrication, material characterization, and multiscale computational simulation.

A Nanoparticle Laser Patterning Process to Fabricate Flexible Electronics

Flexible electronics are attractive for new applications because of their flexible forms as well as properties of light weight and portability. The circuits are usually printed on flexible substrates such as plastic, fabric, and paper, which are delicate and heat sensitive. Traditional photolithography with the use of high temperature and corrosive chemicals is not suitable for flexible substrates. The fabrication of flexible electronics requires fast and low-temperature printing processes in order to minimize the damage of the flexible substrates.

In this research, a high-throughput nanoparticle laser patterning process for flexible electronics is developed, where nanoparticles are sintered with low power laser while they are selectively deposited to enhance printing quality. Copper and silver particles are successfully deposited on paper and polyethylene terephthalate (PET) substrates. To study the process-structure-property relationship, the effects of process parameters on the deposition performance are assessed. The thermal effect of laser on the morphology and porosity of films is observed under scanning electron microscope. Chemical composition of printed pattern is also characterized using X-ray diffractometer. The sensitivity of electromechanical property with respect to the porosities, as a result of different laser power densities, is analyzed. In theoretical studies, a multiscale model of deposition mechanism is developed, where an analytical adhesion model predicts the deposition performance based on laser irradiation, particle size, temperature, elastic-plastic properties of particle and substrate, and deposition velocity. The mechanical properties of nanoparticles are predicted by molecular dynamics simulation to construct the structure-property linkage at nanoscale. A controlled kinetic Monte Carlo simulation model is applied to build process- structure relationship to predict the morphologies of the printing results at mesoscale. The developed process is demonstrated and applied to fabricate hydrophobic and hydrophilic patterns with controlled oxidation levels on PET substrate, and flexible electronics on PET and paper substrate.