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ACS Nano. 2018 Oct 23;12(10):10317-10326. doi: 10.1021/acsnano.8b05552. Epub 2018 Oct 5.

Ultrathin Trilayer Assemblies as Long-Lived Barriers against Water and Ion Penetration in Flexible Bioelectronic Systems.

Author information

Center for Bio-Integrated Electronics , Northwestern University , Evanston , Illinois 60208 , United States.
Frederick Seitz Materials Research Laboratory, Department of Materials Science and Engineering , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States.
State Key Laboratory of Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, and International Research Center for Computational Mechanics , Dalian University of Technology , Dalian 116024 , China.
School of Electrical and Computer Engineering , Purdue University , West Lafayette , Indiana 47907 , United States.
Department of Electrical and Computer Engineering , Northeastern University , Boston , Massachusetts 02115 , United States.
Department of Materials Science and Engineering , Seoul National University , Seoul 08826 , Republic of Korea.
School of Electrical and Electronic Engineering , Yonsei University , Seoul 03722 , Republic of Korea.
Department of Materials Science , Fudan University , Shanghai 200433 , China.
Department of Mechanical Engineering, Civil and Environmental Engineering, and Materials Science and Engineering , Northwestern University , Evanston , Illinois 60208 , United States.
Departments of Materials Science and Engineering, Biomedical Engineering, Neurological Surgery, Chemistry, Mechanical Engineering, Electrical Engineering and Computer Science, Simpson Querrey Institute for Nano/Biotechnology , Northwestern University , Evanston , Illinois 60208 , United States.


Biomedical implants that incorporate active electronics and offer the ability to operate in a safe, stable fashion for long periods of time must incorporate defect-free layers as barriers to biofluid penetration. This paper reports an engineered material approach to this challenge that combines ultrathin, physically transferred films of silicon dioxide (t-SiO2) thermally grown on silicon wafers, with layers of hafnium oxide (HfO2) formed by atomic layer deposition and coatings of parylene (Parylene C) created by chemical vapor deposition, as a dual-sided encapsulation structure for flexible bioelectronic systems. Accelerated aging tests on passive/active components in platforms that incorporate active, silicon-based transistors suggest that this trilayer construct can serve as a robust, long-lived, defect-free barrier to phosphate-buffered saline (PBS) solution at a physiological pH of 7.4. Reactive diffusion modeling and systematic immersion experiments highlight fundamental aspects of water diffusion and hydrolysis behaviors, with results that suggest lifetimes of many decades at physiological conditions. A combination of ion-diffusion tests under continuous electrical bias, measurements of elemental concentration profiles, and temperature-dependent simulations reveals that this encapsulation strategy can also block transport of ions that would otherwise degrade the performance of the underlying electronics. These findings suggest broad utility of this trilayer assembly as a reliable encapsulation strategy for the most demanding applications in chronic biomedical implants and high-performance flexible bioelectronic systems.


chronic implant; flexible bioelectronics; ion diffusion; reactive diffusion modeling; ultrathin encapsulation


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