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Fluorinated Epoxy Siloxane Hybrid Materials for Bio-Fluidic Barrier on Flexible Electronics
Injun Lee1,Wonryung Lee1,Yongho Kim1,Byeong-soo Bae1
Korea Advanced Institute of Science and Technology1
Injun Lee, Wonryung Lee, Yong Ho Kim, and Byeong-Soo Bae
Wearable Platform Materials Technology Center (WMC)
Dept. of Mater. Sci. & Eng., KAIST, Daejeon 34141, Republic of Korea
The barrier is a key component of bio-integrated electronics, protecting the device from the bio-fluid environment and enabling high performance without degradation over time. Recently, the bio-fluidic barrier on the ultra-thin device offers reliable measurement of various bio-signals from even on skin or organ due to the defect-free passivation layer. To meet the requirement of low water permeability, inorganic material based bio-fluidic barriers such as thermal grown SiO2  and bilayer of SiO2/SiNxhave been exhibited superior barrier performance. However, the inorganic materials for the barrier have process incompatibility, including high processing temperature and harsh etching conditions. Thus, the organic materials based on bio-fluidic barriers, such as polyimide(PI) and SU-8 have been also investigated due to their process compatibility. But such organic-based barriers are unstable under the water environment, resulting in unreliable ultra-thin devices for the bio-applications. Therefore, hybrid material for the bio-fluidic barrier that has advantages of both organic and inorganic is needed.
Here, we demonstrate the siloxane(inorganic) based fluorinated epoxy(organic) hybrid materials(FEH) for the bio-fluidic barrier and confirm the barrier performance for the flexible system by using the solution-processed oxide thin-film transistor(TFT)s on ultra-thin polyimide film. Our sol-gel derived FEH is inorganic-organic hybrid materials for the bio-fluid barrier, which is capable of simple spin-coating and UV-patterning by cationic polymerization without additional etching process. Furthermore, FEH exhibits superior water repellency and hydrophobicity compared to other conventional organic films due to the fluorine functional group, which can be confirmed by magnesium soaking test and water contact angle. To evaluate the electrical stability of the barrier in the bio-fluidic environment, we confirm no leakage through defects of films using electrical impedance spectroscopy analysis. To verify the barrier performance in real-time, we demonstrate the solution-processed indium oxide TFTs with the FEH barrier and measure the transfer characteristics in the phosphate-buffered saline (PBS). The oxide TFT, which is vulnerable to water, passivated by FEH barrier films exhibits transfer characteristics with no dramatically change during 16hours in the PBS. Furthermore, to realize the FEH barrier for flexible systems, we demonstrate the solution-processed oxide TFTs on 1μm-thick polyimide film with the FEH barrier and successfully measure the transfer characteristic, which is consistent with the result of TFTs on rigid glass wafer. In conclusion, we envisage the potential of our FEH as a bio-fluidic barrier for future bio-integrated devices and advanced electronics.
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