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Article

Thin Film Encapsulation for LCP-Based Flexible Bioelectronic Implants: Comparison of Different Coating Materials Using Test Methodologies for Life-Time Estimation

1
Department of Microelectronics, Delft University of Technology, 2628 CD Delft, The Netherlands
2
Department of System Integration and Interconnection Technologies, Fraunhofer Institute for Reliability and Micro-Intregration IZM, 13355 Berlin, Germany
3
Picosun Oy, Tietotie 3, 02150 Espoo, Finland
4
CorTec GmbH, 79108 Freiburg, Germany
5
Comelec SA, 2301 La Chaux-de-Fonds, Switzerland
*
Author to whom correspondence should be addressed.
Academic Editor: Nam-Trung Nguyen
Micromachines 2022, 13(4), 544; https://doi.org/10.3390/mi13040544
Received: 25 February 2022 / Revised: 22 March 2022 / Accepted: 28 March 2022 / Published: 30 March 2022
Liquid crystal polymer (LCP) has gained wide interest in the electronics industry largely due to its flexibility, stable insulation and dielectric properties and chip integration capabilities. Recently, LCP has also been investigated as a biocompatible substrate for the fabrication of multielectrode arrays. Realizing a fully implantable LCP-based bioelectronic device, however, still necessitates a low form factor packaging solution to protect the electronics in the body. In this work, we investigate two promising encapsulation coatings based on thin-film technology as the main packaging for LCP-based electronics. Specifically, a HfO2–based nanolaminate ceramic (TFE1) deposited via atomic layer deposition (ALD), and a hybrid Parylene C-ALD multilayer stack (TFE2), both with a silicone finish, were investigated and compared to a reference LCP coating. T-peel, water-vapour transmission rate (WVTR) and long-term electrochemical impedance spectrometry (EIS) tests were performed to evaluate adhesion, barrier properties and overall encapsulation performance of the coatings. Both TFE materials showed stable impedance characteristics while submerged in 60 °C saline, with TFE1-silicone lasting more than 16 months under a continuous 14V DC bias (experiment is ongoing). The results presented in this work show that WVTR is not the main factor in determining lifetime, but the adhesion of the coating to the substrate materials plays a key role in maintaining a stable interface and thus longer lifetimes. View Full-Text
Keywords: flexible bioelectronics; thin-film encapsulation (TFE); liquid crystal polymer (LCP); atomic layer deposition (ALD); Parylene-C (ParC); long-term encapsulation flexible bioelectronics; thin-film encapsulation (TFE); liquid crystal polymer (LCP); atomic layer deposition (ALD); Parylene-C (ParC); long-term encapsulation
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MDPI and ACS Style

Pak, A.; Nanbakhsh, K.; Hölck, O.; Ritasalo, R.; Sousa, M.; Van Gompel, M.; Pahl, B.; Wilson, J.; Kallmayer, C.; Giagka, V. Thin Film Encapsulation for LCP-Based Flexible Bioelectronic Implants: Comparison of Different Coating Materials Using Test Methodologies for Life-Time Estimation. Micromachines 2022, 13, 544. https://doi.org/10.3390/mi13040544

AMA Style

Pak A, Nanbakhsh K, Hölck O, Ritasalo R, Sousa M, Van Gompel M, Pahl B, Wilson J, Kallmayer C, Giagka V. Thin Film Encapsulation for LCP-Based Flexible Bioelectronic Implants: Comparison of Different Coating Materials Using Test Methodologies for Life-Time Estimation. Micromachines. 2022; 13(4):544. https://doi.org/10.3390/mi13040544

Chicago/Turabian Style

Pak, Anna, Kambiz Nanbakhsh, Ole Hölck, Riina Ritasalo, Maria Sousa, Matthias Van Gompel, Barbara Pahl, Joshua Wilson, Christine Kallmayer, and Vasiliki Giagka. 2022. "Thin Film Encapsulation for LCP-Based Flexible Bioelectronic Implants: Comparison of Different Coating Materials Using Test Methodologies for Life-Time Estimation" Micromachines 13, no. 4: 544. https://doi.org/10.3390/mi13040544

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